import "database/sql"
Package sql provides a generic interface around SQL (or SQL-like) databases.
The sql package must be used in conjunction with a database driver. See https://golang.org/s/sqldrivers for a list of drivers.
Drivers that do not support context cancellation will not return until after the query is completed.
For usage examples, see the wiki page at https://golang.org/s/sqlwiki.
Code:
package sql_test
import (
"context"
"database/sql"
"flag"
"log"
"os"
"os/signal"
"time"
)
var pool *sql.DB // Database connection pool.
func Example_openDBCLI() {
id := flag.Int64("id", 0, "person ID to find")
dsn := flag.String("dsn", os.Getenv("DSN"), "connection data source name")
flag.Parse()
if len(*dsn) == 0 {
log.Fatal("missing dsn flag")
}
if *id == 0 {
log.Fatal("missing person ID")
}
var err error
// Opening a driver typically will not attempt to connect to the database.
pool, err = sql.Open("driver-name", *dsn)
if err != nil {
// This will not be a connection error, but a DSN parse error or
// another initialization error.
log.Fatal("unable to use data source name", err)
}
defer pool.Close()
pool.SetConnMaxLifetime(0)
pool.SetMaxIdleConns(3)
pool.SetMaxOpenConns(3)
ctx, stop := context.WithCancel(context.Background())
defer stop()
appSignal := make(chan os.Signal, 3)
signal.Notify(appSignal, os.Interrupt)
go func() {
select {
case <-appSignal:
stop()
}
}()
Ping(ctx)
Query(ctx, *id)
}
// Ping the database to verify DSN provided by the user is valid and the
// server accessible. If the ping fails exit the program with an error.
func Ping(ctx context.Context) {
ctx, cancel := context.WithTimeout(ctx, 1*time.Second)
defer cancel()
if err := pool.PingContext(ctx); err != nil {
log.Fatalf("unable to connect to database: %v", err)
}
}
// Query the database for the information requested and prints the results.
// If the query fails exit the program with an error.
func Query(ctx context.Context, id int64) {
ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
defer cancel()
var name string
err := pool.QueryRowContext(ctx, "select p.name from people as p where p.id = :id;", sql.Named("id", id)).Scan(&name)
if err != nil {
log.Fatal("unable to execute search query", err)
}
log.Println("name=", name)
}
Code:
package sql_test
import (
"context"
"database/sql"
"encoding/json"
"fmt"
"io"
"log"
"net/http"
"time"
)
func Example_openDBService() {
// Opening a driver typically will not attempt to connect to the database.
db, err := sql.Open("driver-name", "database=test1")
if err != nil {
// This will not be a connection error, but a DSN parse error or
// another initialization error.
log.Fatal(err)
}
db.SetConnMaxLifetime(0)
db.SetMaxIdleConns(50)
db.SetMaxOpenConns(50)
s := &Service{db: db}
http.ListenAndServe(":8080", s)
}
type Service struct {
db *sql.DB
}
func (s *Service) ServeHTTP(w http.ResponseWriter, r *http.Request) {
db := s.db
switch r.URL.Path {
default:
http.Error(w, "not found", http.StatusNotFound)
return
case "/healthz":
ctx, cancel := context.WithTimeout(r.Context(), 1*time.Second)
defer cancel()
err := s.db.PingContext(ctx)
if err != nil {
http.Error(w, fmt.Sprintf("db down: %v", err), http.StatusFailedDependency)
return
}
w.WriteHeader(http.StatusOK)
return
case "/quick-action":
// This is a short SELECT. Use the request context as the base of
// the context timeout.
ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
defer cancel()
id := 5
org := 10
var name string
err := db.QueryRowContext(ctx, `
select
p.name
from
people as p
join organization as o on p.organization = o.id
where
p.id = :id
and o.id = :org
;`,
sql.Named("id", id),
sql.Named("org", org),
).Scan(&name)
if err != nil {
if err == sql.ErrNoRows {
http.Error(w, "not found", http.StatusNotFound)
return
}
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
io.WriteString(w, name)
return
case "/long-action":
// This is a long SELECT. Use the request context as the base of
// the context timeout, but give it some time to finish. If
// the client cancels before the query is done the query will also
// be canceled.
ctx, cancel := context.WithTimeout(r.Context(), 60*time.Second)
defer cancel()
var names []string
rows, err := db.QueryContext(ctx, "select p.name from people as p where p.active = true;")
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
for rows.Next() {
var name string
err = rows.Scan(&name)
if err != nil {
break
}
names = append(names, name)
}
// Check for errors during rows "Close".
// This may be more important if multiple statements are executed
// in a single batch and rows were written as well as read.
if closeErr := rows.Close(); closeErr != nil {
http.Error(w, closeErr.Error(), http.StatusInternalServerError)
return
}
// Check for row scan error.
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
// Check for errors during row iteration.
if err = rows.Err(); err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
json.NewEncoder(w).Encode(names)
return
case "/async-action":
// This action has side effects that we want to preserve
// even if the client cancels the HTTP request part way through.
// For this we do not use the http request context as a base for
// the timeout.
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
var orderRef = "ABC123"
tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
_, err = tx.ExecContext(ctx, "stored_proc_name", orderRef)
if err != nil {
tx.Rollback()
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
err = tx.Commit()
if err != nil {
http.Error(w, "action in unknown state, check state before attempting again", http.StatusInternalServerError)
return
}
w.WriteHeader(http.StatusOK)
return
}
}
var ErrConnDone = errors.New("sql: connection is already closed")
ErrConnDone is returned by any operation that is performed on a connection that has already been returned to the connection pool.
var ErrNoRows = errors.New("sql: no rows in result set")
ErrNoRows is returned by Scan when QueryRow doesn't return a row. In such a case, QueryRow returns a placeholder *Row value that defers this error until a Scan.
var ErrTxDone = errors.New("sql: transaction has already been committed or rolled back")
ErrTxDone is returned by any operation that is performed on a transaction that has already been committed or rolled back.
func Drivers() []string
Drivers returns a sorted list of the names of the registered drivers.
func Register(name string, driver driver.Driver)
Register makes a database driver available by the provided name. If Register is called twice with the same name or if driver is nil, it panics.
type ColumnType struct {
// contains filtered or unexported fields
}
ColumnType contains the name and type of a column.
func (ci *ColumnType) DatabaseTypeName() string
DatabaseTypeName returns the database system name of the column type. If an empty string is returned the driver type name is not supported. Consult your driver documentation for a list of driver data types. Length specifiers are not included. Common type include "VARCHAR", "TEXT", "NVARCHAR", "DECIMAL", "BOOL", "INT", "BIGINT".
func (ci *ColumnType) DecimalSize() (precision, scale int64, ok bool)
DecimalSize returns the scale and precision of a decimal type. If not applicable or if not supported ok is false.
func (ci *ColumnType) Length() (length int64, ok bool)
Length returns the column type length for variable length column types such as text and binary field types. If the type length is unbounded the value will be math.MaxInt64 (any database limits will still apply). If the column type is not variable length, such as an int, or if not supported by the driver ok is false.
func (ci *ColumnType) Name() string
Name returns the name or alias of the column.
func (ci *ColumnType) Nullable() (nullable, ok bool)
Nullable reports whether the column may be null. If a driver does not support this property ok will be false.
func (ci *ColumnType) ScanType() reflect.Type
ScanType returns a Go type suitable for scanning into using Rows.Scan. If a driver does not support this property ScanType will return the type of an empty interface.
type Conn struct {
// contains filtered or unexported fields
}
Conn represents a single database connection rather than a pool of database connections. Prefer running queries from DB unless there is a specific need for a continuous single database connection.
A Conn must call Close to return the connection to the database pool and may do so concurrently with a running query.
After a call to Close, all operations on the connection fail with ErrConnDone.
func (c *Conn) BeginTx(ctx context.Context, opts *TxOptions) (*Tx, error)
BeginTx starts a transaction.
The provided context is used until the transaction is committed or rolled back. If the context is canceled, the sql package will roll back the transaction. Tx.Commit will return an error if the context provided to BeginTx is canceled.
The provided TxOptions is optional and may be nil if defaults should be used. If a non-default isolation level is used that the driver doesn't support, an error will be returned.
Code:
tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
if err != nil {
log.Fatal(err)
}
id := 37
_, execErr := tx.Exec(`UPDATE users SET status = ? WHERE id = ?`, "paid", id)
if execErr != nil {
_ = tx.Rollback()
log.Fatal(execErr)
}
if err := tx.Commit(); err != nil {
log.Fatal(err)
}
func (c *Conn) Close() error
Close returns the connection to the connection pool. All operations after a Close will return with ErrConnDone. Close is safe to call concurrently with other operations and will block until all other operations finish. It may be useful to first cancel any used context and then call close directly after.
func (c *Conn) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error)
ExecContext executes a query without returning any rows. The args are for any placeholder parameters in the query.
Code:
// A *DB is a pool of connections. Call Conn to reserve a connection for // exclusive use. conn, err := db.Conn(ctx) if err != nil { log.Fatal(err) } defer conn.Close() // Return the connection to the pool. id := 41 result, err := conn.ExecContext(ctx, `UPDATE balances SET balance = balance + 10 WHERE user_id = ?;`, id) if err != nil { log.Fatal(err) } rows, err := result.RowsAffected() if err != nil { log.Fatal(err) } if rows != 1 { log.Fatalf("expected single row affected, got %d rows affected", rows) }
func (c *Conn) PingContext(ctx context.Context) error
PingContext verifies the connection to the database is still alive.
func (c *Conn) PrepareContext(ctx context.Context, query string) (*Stmt, error)
PrepareContext creates a prepared statement for later queries or executions. Multiple queries or executions may be run concurrently from the returned statement. The caller must call the statement's Close method when the statement is no longer needed.
The provided context is used for the preparation of the statement, not for the execution of the statement.
func (c *Conn) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error)
QueryContext executes a query that returns rows, typically a SELECT. The args are for any placeholder parameters in the query.
func (c *Conn) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row
QueryRowContext executes a query that is expected to return at most one row. QueryRowContext always returns a non-nil value. Errors are deferred until Row's Scan method is called. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
func (c *Conn) Raw(f func(driverConn interface{}) error) (err error)
Raw executes f exposing the underlying driver connection for the duration of f. The driverConn must not be used outside of f.
Once f returns and err is nil, the Conn will continue to be usable until Conn.Close is called.
type DB struct {
// contains filtered or unexported fields
}
DB is a database handle representing a pool of zero or more underlying connections. It's safe for concurrent use by multiple goroutines.
The sql package creates and frees connections automatically; it also maintains a free pool of idle connections. If the database has a concept of per-connection state, such state can be reliably observed within a transaction (Tx) or connection (Conn). Once DB.Begin is called, the returned Tx is bound to a single connection. Once Commit or Rollback is called on the transaction, that transaction's connection is returned to DB's idle connection pool. The pool size can be controlled with SetMaxIdleConns.
func Open(driverName, dataSourceName string) (*DB, error)
Open opens a database specified by its database driver name and a driver-specific data source name, usually consisting of at least a database name and connection information.
Most users will open a database via a driver-specific connection helper function that returns a *DB. No database drivers are included in the Go standard library. See https://golang.org/s/sqldrivers for a list of third-party drivers.
Open may just validate its arguments without creating a connection to the database. To verify that the data source name is valid, call Ping.
The returned DB is safe for concurrent use by multiple goroutines and maintains its own pool of idle connections. Thus, the Open function should be called just once. It is rarely necessary to close a DB.
func OpenDB(c driver.Connector) *DB
OpenDB opens a database using a Connector, allowing drivers to bypass a string based data source name.
Most users will open a database via a driver-specific connection helper function that returns a *DB. No database drivers are included in the Go standard library. See https://golang.org/s/sqldrivers for a list of third-party drivers.
OpenDB may just validate its arguments without creating a connection to the database. To verify that the data source name is valid, call Ping.
The returned DB is safe for concurrent use by multiple goroutines and maintains its own pool of idle connections. Thus, the OpenDB function should be called just once. It is rarely necessary to close a DB.
func (db *DB) Begin() (*Tx, error)
Begin starts a transaction. The default isolation level is dependent on the driver.
func (db *DB) BeginTx(ctx context.Context, opts *TxOptions) (*Tx, error)
BeginTx starts a transaction.
The provided context is used until the transaction is committed or rolled back. If the context is canceled, the sql package will roll back the transaction. Tx.Commit will return an error if the context provided to BeginTx is canceled.
The provided TxOptions is optional and may be nil if defaults should be used. If a non-default isolation level is used that the driver doesn't support, an error will be returned.
func (db *DB) Close() error
Close closes the database and prevents new queries from starting. Close then waits for all queries that have started processing on the server to finish.
It is rare to Close a DB, as the DB handle is meant to be long-lived and shared between many goroutines.
func (db *DB) Conn(ctx context.Context) (*Conn, error)
Conn returns a single connection by either opening a new connection or returning an existing connection from the connection pool. Conn will block until either a connection is returned or ctx is canceled. Queries run on the same Conn will be run in the same database session.
Every Conn must be returned to the database pool after use by calling Conn.Close.
func (db *DB) Driver() driver.Driver
Driver returns the database's underlying driver.
func (db *DB) Exec(query string, args ...interface{}) (Result, error)
Exec executes a query without returning any rows. The args are for any placeholder parameters in the query.
func (db *DB) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error)
ExecContext executes a query without returning any rows. The args are for any placeholder parameters in the query.
Code:
id := 47
result, err := db.ExecContext(ctx, "UPDATE balances SET balance = balance + 10 WHERE user_id = ?", id)
if err != nil {
log.Fatal(err)
}
rows, err := result.RowsAffected()
if err != nil {
log.Fatal(err)
}
if rows != 1 {
log.Fatalf("expected to affect 1 row, affected %d", rows)
}
func (db *DB) Ping() error
Ping verifies a connection to the database is still alive, establishing a connection if necessary.
func (db *DB) PingContext(ctx context.Context) error
PingContext verifies a connection to the database is still alive, establishing a connection if necessary.
Code:
// Ping and PingContext may be used to determine if communication with // the database server is still possible. // // When used in a command line application Ping may be used to establish // that further queries are possible; that the provided DSN is valid. // // When used in long running service Ping may be part of the health // checking system. ctx, cancel := context.WithTimeout(ctx, 1*time.Second) defer cancel() status := "up" if err := db.PingContext(ctx); err != nil { status = "down" } log.Println(status)
func (db *DB) Prepare(query string) (*Stmt, error)
Prepare creates a prepared statement for later queries or executions. Multiple queries or executions may be run concurrently from the returned statement. The caller must call the statement's Close method when the statement is no longer needed.
Code:
projects := []struct {
mascot string
release int
}{
{"tux", 1991},
{"duke", 1996},
{"gopher", 2009},
{"moby dock", 2013},
}
stmt, err := db.Prepare("INSERT INTO projects(id, mascot, release, category) VALUES( ?, ?, ?, ? )")
if err != nil {
log.Fatal(err)
}
defer stmt.Close() // Prepared statements take up server resources and should be closed after use.
for id, project := range projects {
if _, err := stmt.Exec(id+1, project.mascot, project.release, "open source"); err != nil {
log.Fatal(err)
}
}
func (db *DB) PrepareContext(ctx context.Context, query string) (*Stmt, error)
PrepareContext creates a prepared statement for later queries or executions. Multiple queries or executions may be run concurrently from the returned statement. The caller must call the statement's Close method when the statement is no longer needed.
The provided context is used for the preparation of the statement, not for the execution of the statement.
func (db *DB) Query(query string, args ...interface{}) (*Rows, error)
Query executes a query that returns rows, typically a SELECT. The args are for any placeholder parameters in the query.
Code:
age := 27
q := `
create temp table uid (id bigint); -- Create temp table for queries.
insert into uid
select id from users where age < ?; -- Populate temp table.
-- First result set.
select
users.id, name
from
users
join uid on users.id = uid.id
;
-- Second result set.
select
ur.user, ur.role
from
user_roles as ur
join uid on uid.id = ur.user
;
`
rows, err := db.Query(q, age)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
for rows.Next() {
var (
id int64
name string
)
if err := rows.Scan(&id, &name); err != nil {
log.Fatal(err)
}
log.Printf("id %d name is %s\n", id, name)
}
if !rows.NextResultSet() {
log.Fatalf("expected more result sets: %v", rows.Err())
}
var roleMap = map[int64]string{
1: "user",
2: "admin",
3: "gopher",
}
for rows.Next() {
var (
id int64
role int64
)
if err := rows.Scan(&id, &role); err != nil {
log.Fatal(err)
}
log.Printf("id %d has role %s\n", id, roleMap[role])
}
if err := rows.Err(); err != nil {
log.Fatal(err)
}
func (db *DB) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error)
QueryContext executes a query that returns rows, typically a SELECT. The args are for any placeholder parameters in the query.
Code:
age := 27
rows, err := db.QueryContext(ctx, "SELECT name FROM users WHERE age=?", age)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
names := make([]string, 0)
for rows.Next() {
var name string
if err := rows.Scan(&name); err != nil {
// Check for a scan error.
// Query rows will be closed with defer.
log.Fatal(err)
}
names = append(names, name)
}
// If the database is being written to ensure to check for Close
// errors that may be returned from the driver. The query may
// encounter an auto-commit error and be forced to rollback changes.
rerr := rows.Close()
if rerr != nil {
log.Fatal(err)
}
// Rows.Err will report the last error encountered by Rows.Scan.
if err := rows.Err(); err != nil {
log.Fatal(err)
}
fmt.Printf("%s are %d years old", strings.Join(names, ", "), age)
func (db *DB) QueryRow(query string, args ...interface{}) *Row
QueryRow executes a query that is expected to return at most one row. QueryRow always returns a non-nil value. Errors are deferred until Row's Scan method is called. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
func (db *DB) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row
QueryRowContext executes a query that is expected to return at most one row. QueryRowContext always returns a non-nil value. Errors are deferred until Row's Scan method is called. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
Code:
id := 123
var username string
var created time.Time
err := db.QueryRowContext(ctx, "SELECT username, created_at FROM users WHERE id=?", id).Scan(&username, &created)
switch {
case err == sql.ErrNoRows:
log.Printf("no user with id %d\n", id)
case err != nil:
log.Fatalf("query error: %v\n", err)
default:
log.Printf("username is %q, account created on %s\n", username, created)
}
func (db *DB) SetConnMaxLifetime(d time.Duration)
SetConnMaxLifetime sets the maximum amount of time a connection may be reused.
Expired connections may be closed lazily before reuse.
If d <= 0, connections are reused forever.
func (db *DB) SetMaxIdleConns(n int)
SetMaxIdleConns sets the maximum number of connections in the idle connection pool.
If MaxOpenConns is greater than 0 but less than the new MaxIdleConns, then the new MaxIdleConns will be reduced to match the MaxOpenConns limit.
If n <= 0, no idle connections are retained.
The default max idle connections is currently 2. This may change in a future release.
func (db *DB) SetMaxOpenConns(n int)
SetMaxOpenConns sets the maximum number of open connections to the database.
If MaxIdleConns is greater than 0 and the new MaxOpenConns is less than MaxIdleConns, then MaxIdleConns will be reduced to match the new MaxOpenConns limit.
If n <= 0, then there is no limit on the number of open connections. The default is 0 (unlimited).
func (db *DB) Stats() DBStats
Stats returns database statistics.
type DBStats struct {
MaxOpenConnections int // Maximum number of open connections to the database.
// Pool Status
OpenConnections int // The number of established connections both in use and idle.
InUse int // The number of connections currently in use.
Idle int // The number of idle connections.
// Counters
WaitCount int64 // The total number of connections waited for.
WaitDuration time.Duration // The total time blocked waiting for a new connection.
MaxIdleClosed int64 // The total number of connections closed due to SetMaxIdleConns.
MaxLifetimeClosed int64 // The total number of connections closed due to SetConnMaxLifetime.
}
DBStats contains database statistics.
type IsolationLevel int
IsolationLevel is the transaction isolation level used in TxOptions.
const (
LevelDefault IsolationLevel = iota
LevelReadUncommitted
LevelReadCommitted
LevelWriteCommitted
LevelRepeatableRead
LevelSnapshot
LevelSerializable
LevelLinearizable
)
Various isolation levels that drivers may support in BeginTx. If a driver does not support a given isolation level an error may be returned.
See https://en.wikipedia.org/wiki/Isolation_(database_systems)#Isolation_levels.
func (i IsolationLevel) String() string
String returns the name of the transaction isolation level.
type NamedArg struct {
// Name is the name of the parameter placeholder.
//
// If empty, the ordinal position in the argument list will be
// used.
//
// Name must omit any symbol prefix.
Name string
// Value is the value of the parameter.
// It may be assigned the same value types as the query
// arguments.
Value interface{}
// contains filtered or unexported fields
}
A NamedArg is a named argument. NamedArg values may be used as arguments to Query or Exec and bind to the corresponding named parameter in the SQL statement.
For a more concise way to create NamedArg values, see the Named function.
func Named(name string, value interface{}) NamedArg
Named provides a more concise way to create NamedArg values.
Example usage:
db.ExecContext(ctx, `
delete from Invoice
where
TimeCreated < @end
and TimeCreated >= @start;`,
sql.Named("start", startTime),
sql.Named("end", endTime),
)
type NullBool struct {
Bool bool
Valid bool // Valid is true if Bool is not NULL
}
NullBool represents a bool that may be null. NullBool implements the Scanner interface so it can be used as a scan destination, similar to NullString.
func (n *NullBool) Scan(value interface{}) error
Scan implements the Scanner interface.
func (n NullBool) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type NullFloat64 struct {
Float64 float64
Valid bool // Valid is true if Float64 is not NULL
}
NullFloat64 represents a float64 that may be null. NullFloat64 implements the Scanner interface so it can be used as a scan destination, similar to NullString.
func (n *NullFloat64) Scan(value interface{}) error
Scan implements the Scanner interface.
func (n NullFloat64) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type NullInt32 struct {
Int32 int32
Valid bool // Valid is true if Int32 is not NULL
}
NullInt32 represents an int32 that may be null. NullInt32 implements the Scanner interface so it can be used as a scan destination, similar to NullString.
func (n *NullInt32) Scan(value interface{}) error
Scan implements the Scanner interface.
func (n NullInt32) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type NullInt64 struct {
Int64 int64
Valid bool // Valid is true if Int64 is not NULL
}
NullInt64 represents an int64 that may be null. NullInt64 implements the Scanner interface so it can be used as a scan destination, similar to NullString.
func (n *NullInt64) Scan(value interface{}) error
Scan implements the Scanner interface.
func (n NullInt64) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type NullString struct {
String string
Valid bool // Valid is true if String is not NULL
}
NullString represents a string that may be null. NullString implements the Scanner interface so it can be used as a scan destination:
var s NullString
err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
...
if s.Valid {
// use s.String
} else {
// NULL value
}
func (ns *NullString) Scan(value interface{}) error
Scan implements the Scanner interface.
func (ns NullString) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type NullTime struct {
Time time.Time
Valid bool // Valid is true if Time is not NULL
}
NullTime represents a time.Time that may be null. NullTime implements the Scanner interface so it can be used as a scan destination, similar to NullString.
func (n *NullTime) Scan(value interface{}) error
Scan implements the Scanner interface.
func (n NullTime) Value() (driver.Value, error)
Value implements the driver Valuer interface.
type Out struct {
// Dest is a pointer to the value that will be set to the result of the
// stored procedure's OUTPUT parameter.
Dest interface{}
// In is whether the parameter is an INOUT parameter. If so, the input value to the stored
// procedure is the dereferenced value of Dest's pointer, which is then replaced with
// the output value.
In bool
// contains filtered or unexported fields
}
Out may be used to retrieve OUTPUT value parameters from stored procedures.
Not all drivers and databases support OUTPUT value parameters.
Example usage:
var outArg string
_, err := db.ExecContext(ctx, "ProcName", sql.Named("Arg1", sql.Out{Dest: &outArg}))
type RawBytes []byte
RawBytes is a byte slice that holds a reference to memory owned by the database itself. After a Scan into a RawBytes, the slice is only valid until the next call to Next, Scan, or Close.
type Result interface {
// LastInsertId returns the integer generated by the database
// in response to a command. Typically this will be from an
// "auto increment" column when inserting a new row. Not all
// databases support this feature, and the syntax of such
// statements varies.
LastInsertId() (int64, error)
// RowsAffected returns the number of rows affected by an
// update, insert, or delete. Not every database or database
// driver may support this.
RowsAffected() (int64, error)
}
A Result summarizes an executed SQL command.
type Row struct {
// contains filtered or unexported fields
}
Row is the result of calling QueryRow to select a single row.
func (r *Row) Scan(dest ...interface{}) error
Scan copies the columns from the matched row into the values pointed at by dest. See the documentation on Rows.Scan for details. If more than one row matches the query, Scan uses the first row and discards the rest. If no row matches the query, Scan returns ErrNoRows.
type Rows struct {
// contains filtered or unexported fields
}
Rows is the result of a query. Its cursor starts before the first row of the result set. Use Next to advance from row to row.
Code:
age := 27
rows, err := db.QueryContext(ctx, "SELECT name FROM users WHERE age=?", age)
if err != nil {
log.Fatal(err)
}
defer rows.Close()
names := make([]string, 0)
for rows.Next() {
var name string
if err := rows.Scan(&name); err != nil {
log.Fatal(err)
}
names = append(names, name)
}
// Check for errors from iterating over rows.
if err := rows.Err(); err != nil {
log.Fatal(err)
}
log.Printf("%s are %d years old", strings.Join(names, ", "), age)
func (rs *Rows) Close() error
Close closes the Rows, preventing further enumeration. If Next is called and returns false and there are no further result sets, the Rows are closed automatically and it will suffice to check the result of Err. Close is idempotent and does not affect the result of Err.
func (rs *Rows) ColumnTypes() ([]*ColumnType, error)
ColumnTypes returns column information such as column type, length, and nullable. Some information may not be available from some drivers.
func (rs *Rows) Columns() ([]string, error)
Columns returns the column names. Columns returns an error if the rows are closed.
func (rs *Rows) Err() error
Err returns the error, if any, that was encountered during iteration. Err may be called after an explicit or implicit Close.
func (rs *Rows) Next() bool
Next prepares the next result row for reading with the Scan method. It returns true on success, or false if there is no next result row or an error happened while preparing it. Err should be consulted to distinguish between the two cases.
Every call to Scan, even the first one, must be preceded by a call to Next.
func (rs *Rows) NextResultSet() bool
NextResultSet prepares the next result set for reading. It reports whether there is further result sets, or false if there is no further result set or if there is an error advancing to it. The Err method should be consulted to distinguish between the two cases.
After calling NextResultSet, the Next method should always be called before scanning. If there are further result sets they may not have rows in the result set.
func (rs *Rows) Scan(dest ...interface{}) error
Scan copies the columns in the current row into the values pointed at by dest. The number of values in dest must be the same as the number of columns in Rows.
Scan converts columns read from the database into the following common Go types and special types provided by the sql package:
*string
*[]byte
*int, *int8, *int16, *int32, *int64
*uint, *uint8, *uint16, *uint32, *uint64
*bool
*float32, *float64
*interface{}
*RawBytes
*Rows (cursor value)
any type implementing Scanner (see Scanner docs)
In the most simple case, if the type of the value from the source column is an integer, bool or string type T and dest is of type *T, Scan simply assigns the value through the pointer.
Scan also converts between string and numeric types, as long as no information would be lost. While Scan stringifies all numbers scanned from numeric database columns into *string, scans into numeric types are checked for overflow. For example, a float64 with value 300 or a string with value "300" can scan into a uint16, but not into a uint8, though float64(255) or "255" can scan into a uint8. One exception is that scans of some float64 numbers to strings may lose information when stringifying. In general, scan floating point columns into *float64.
If a dest argument has type *[]byte, Scan saves in that argument a copy of the corresponding data. The copy is owned by the caller and can be modified and held indefinitely. The copy can be avoided by using an argument of type *RawBytes instead; see the documentation for RawBytes for restrictions on its use.
If an argument has type *interface{}, Scan copies the value provided by the underlying driver without conversion. When scanning from a source value of type []byte to *interface{}, a copy of the slice is made and the caller owns the result.
Source values of type time.Time may be scanned into values of type *time.Time, *interface{}, *string, or *[]byte. When converting to the latter two, time.RFC3339Nano is used.
Source values of type bool may be scanned into types *bool, *interface{}, *string, *[]byte, or *RawBytes.
For scanning into *bool, the source may be true, false, 1, 0, or string inputs parseable by strconv.ParseBool.
Scan can also convert a cursor returned from a query, such as "select cursor(select * from my_table) from dual", into a *Rows value that can itself be scanned from. The parent select query will close any cursor *Rows if the parent *Rows is closed.
type Scanner interface {
// Scan assigns a value from a database driver.
//
// The src value will be of one of the following types:
//
// int64
// float64
// bool
// []byte
// string
// time.Time
// nil - for NULL values
//
// An error should be returned if the value cannot be stored
// without loss of information.
//
// Reference types such as []byte are only valid until the next call to Scan
// and should not be retained. Their underlying memory is owned by the driver.
// If retention is necessary, copy their values before the next call to Scan.
Scan(src interface{}) error
}
Scanner is an interface used by Scan.
type Stmt struct {
// contains filtered or unexported fields
}
Stmt is a prepared statement. A Stmt is safe for concurrent use by multiple goroutines.
If a Stmt is prepared on a Tx or Conn, it will be bound to a single underlying connection forever. If the Tx or Conn closes, the Stmt will become unusable and all operations will return an error. If a Stmt is prepared on a DB, it will remain usable for the lifetime of the DB. When the Stmt needs to execute on a new underlying connection, it will prepare itself on the new connection automatically.
Code:
// In normal use, create one Stmt when your process starts. stmt, err := db.PrepareContext(ctx, "SELECT username FROM users WHERE id = ?") if err != nil { log.Fatal(err) } defer stmt.Close() // Then reuse it each time you need to issue the query. id := 43 var username string err = stmt.QueryRowContext(ctx, id).Scan(&username) switch { case err == sql.ErrNoRows: log.Fatalf("no user with id %d", id) case err != nil: log.Fatal(err) default: log.Printf("username is %s\n", username) }
func (s *Stmt) Close() error
Close closes the statement.
func (s *Stmt) Exec(args ...interface{}) (Result, error)
Exec executes a prepared statement with the given arguments and returns a Result summarizing the effect of the statement.
func (s *Stmt) ExecContext(ctx context.Context, args ...interface{}) (Result, error)
ExecContext executes a prepared statement with the given arguments and returns a Result summarizing the effect of the statement.
func (s *Stmt) Query(args ...interface{}) (*Rows, error)
Query executes a prepared query statement with the given arguments and returns the query results as a *Rows.
func (s *Stmt) QueryContext(ctx context.Context, args ...interface{}) (*Rows, error)
QueryContext executes a prepared query statement with the given arguments and returns the query results as a *Rows.
func (s *Stmt) QueryRow(args ...interface{}) *Row
QueryRow executes a prepared query statement with the given arguments. If an error occurs during the execution of the statement, that error will be returned by a call to Scan on the returned *Row, which is always non-nil. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
Example usage:
var name string err := nameByUseridStmt.QueryRow(id).Scan(&name)
func (s *Stmt) QueryRowContext(ctx context.Context, args ...interface{}) *Row
QueryRowContext executes a prepared query statement with the given arguments. If an error occurs during the execution of the statement, that error will be returned by a call to Scan on the returned *Row, which is always non-nil. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
Code:
// In normal use, create one Stmt when your process starts. stmt, err := db.PrepareContext(ctx, "SELECT username FROM users WHERE id = ?") if err != nil { log.Fatal(err) } defer stmt.Close() // Then reuse it each time you need to issue the query. id := 43 var username string err = stmt.QueryRowContext(ctx, id).Scan(&username) switch { case err == sql.ErrNoRows: log.Fatalf("no user with id %d", id) case err != nil: log.Fatal(err) default: log.Printf("username is %s\n", username) }
type Tx struct {
// contains filtered or unexported fields
}
Tx is an in-progress database transaction.
A transaction must end with a call to Commit or Rollback.
After a call to Commit or Rollback, all operations on the transaction fail with ErrTxDone.
The statements prepared for a transaction by calling the transaction's Prepare or Stmt methods are closed by the call to Commit or Rollback.
func (tx *Tx) Commit() error
Commit commits the transaction.
func (tx *Tx) Exec(query string, args ...interface{}) (Result, error)
Exec executes a query that doesn't return rows. For example: an INSERT and UPDATE.
func (tx *Tx) ExecContext(ctx context.Context, query string, args ...interface{}) (Result, error)
ExecContext executes a query that doesn't return rows. For example: an INSERT and UPDATE.
Code:
tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
if err != nil {
log.Fatal(err)
}
id := 37
_, execErr := tx.ExecContext(ctx, "UPDATE users SET status = ? WHERE id = ?", "paid", id)
if execErr != nil {
if rollbackErr := tx.Rollback(); rollbackErr != nil {
log.Fatalf("update failed: %v, unable to rollback: %v\n", execErr, rollbackErr)
}
log.Fatalf("update failed: %v", execErr)
}
if err := tx.Commit(); err != nil {
log.Fatal(err)
}
func (tx *Tx) Prepare(query string) (*Stmt, error)
Prepare creates a prepared statement for use within a transaction.
The returned statement operates within the transaction and can no longer be used once the transaction has been committed or rolled back.
To use an existing prepared statement on this transaction, see Tx.Stmt.
Code:
projects := []struct {
mascot string
release int
}{
{"tux", 1991},
{"duke", 1996},
{"gopher", 2009},
{"moby dock", 2013},
}
tx, err := db.Begin()
if err != nil {
log.Fatal(err)
}
defer tx.Rollback() // The rollback will be ignored if the tx has been committed later in the function.
stmt, err := tx.Prepare("INSERT INTO projects(id, mascot, release, category) VALUES( ?, ?, ?, ? )")
if err != nil {
log.Fatal(err)
}
defer stmt.Close() // Prepared statements take up server resources and should be closed after use.
for id, project := range projects {
if _, err := stmt.Exec(id+1, project.mascot, project.release, "open source"); err != nil {
log.Fatal(err)
}
}
if err := tx.Commit(); err != nil {
log.Fatal(err)
}
func (tx *Tx) PrepareContext(ctx context.Context, query string) (*Stmt, error)
PrepareContext creates a prepared statement for use within a transaction.
The returned statement operates within the transaction and will be closed when the transaction has been committed or rolled back.
To use an existing prepared statement on this transaction, see Tx.Stmt.
The provided context will be used for the preparation of the context, not for the execution of the returned statement. The returned statement will run in the transaction context.
func (tx *Tx) Query(query string, args ...interface{}) (*Rows, error)
Query executes a query that returns rows, typically a SELECT.
func (tx *Tx) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error)
QueryContext executes a query that returns rows, typically a SELECT.
func (tx *Tx) QueryRow(query string, args ...interface{}) *Row
QueryRow executes a query that is expected to return at most one row. QueryRow always returns a non-nil value. Errors are deferred until Row's Scan method is called. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
func (tx *Tx) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row
QueryRowContext executes a query that is expected to return at most one row. QueryRowContext always returns a non-nil value. Errors are deferred until Row's Scan method is called. If the query selects no rows, the *Row's Scan will return ErrNoRows. Otherwise, the *Row's Scan scans the first selected row and discards the rest.
func (tx *Tx) Rollback() error
Rollback aborts the transaction.
Code:
tx, err := db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelSerializable})
if err != nil {
log.Fatal(err)
}
id := 53
_, err = tx.ExecContext(ctx, "UPDATE drivers SET status = ? WHERE id = ?;", "assigned", id)
if err != nil {
if rollbackErr := tx.Rollback(); rollbackErr != nil {
log.Fatalf("update drivers: unable to rollback: %v", rollbackErr)
}
log.Fatal(err)
}
_, err = tx.ExecContext(ctx, "UPDATE pickups SET driver_id = $1;", id)
if err != nil {
if rollbackErr := tx.Rollback(); rollbackErr != nil {
log.Fatalf("update failed: %v, unable to back: %v", err, rollbackErr)
}
log.Fatal(err)
}
if err := tx.Commit(); err != nil {
log.Fatal(err)
}
func (tx *Tx) Stmt(stmt *Stmt) *Stmt
Stmt returns a transaction-specific prepared statement from an existing statement.
Example:
updateMoney, err := db.Prepare("UPDATE balance SET money=money+? WHERE id=?")
...
tx, err := db.Begin()
...
res, err := tx.Stmt(updateMoney).Exec(123.45, 98293203)
The returned statement operates within the transaction and will be closed when the transaction has been committed or rolled back.
func (tx *Tx) StmtContext(ctx context.Context, stmt *Stmt) *Stmt
StmtContext returns a transaction-specific prepared statement from an existing statement.
Example:
updateMoney, err := db.Prepare("UPDATE balance SET money=money+? WHERE id=?")
...
tx, err := db.Begin()
...
res, err := tx.StmtContext(ctx, updateMoney).Exec(123.45, 98293203)
The provided context is used for the preparation of the statement, not for the execution of the statement.
The returned statement operates within the transaction and will be closed when the transaction has been committed or rolled back.
type TxOptions struct {
// Isolation is the transaction isolation level.
// If zero, the driver or database's default level is used.
Isolation IsolationLevel
ReadOnly bool
}
TxOptions holds the transaction options to be used in DB.BeginTx.