wpdb::select( string $db, mysqli $dbh = null )
- Since
- 0.71
- Source
wp-includes/class-wpdb.php:1192
Description
The database name will be changed based on the current database connection.
On failure, the execution will bail and display a DB error.
Compatibility
- WordPress
- since 0.71
- PHP
- 7.4–8.6-dev
- 6.7.7
- 6.8.8
- 6.9.7
- 7.0.4
- 7.1.0
Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.
Parameters
$dbstring- Database name.
$dbhmysqlioptional- Database connection.
Defaults to the current database handle.Default:null
Performance profile
How much work a call to wpdb::select() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.
- Cost class
- Trivial
- Scaling
- Constant
- Instructions
- 11–104
- Plugin surface
- None
- Called by
- 1
Touches nothing outside its own arguments.
No loop in the body: the same number of instructions runs whatever you pass in.
Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 104.
Nothing here hands control to plugin code.
1 place in core call this, so the cost is paid more often than your own code shows.
What one call costs · 3 distinct outcomes
One number would be a lie: the work depends on which branch runs. These are every distinct cost wpdb::select() can have, taken from its control-flow graph on PHP 8.5.
| When | Instructions | Calls it makes |
|---|---|---|
| always | 11–12 | mysqli_select_db() |
did_action() | 17–18 | mysqli_select_db(), did_action() |
!did_action() | 103–104 | mysqli_select_db(), did_action(), wp_load_translations_early(), __(), __(), htmlspecialchars(), sprintf(), __(), __(), htmlspecialchars(), htmlspecialchars(), sprintf(), __(), htmlspecialchars(), sprintf(), __(), __(), sprintf(), ->bail() |
Across PHP versions
Compiles the same on PHP 7.4, 8.1, 8.2, 8.3, 8.4, 8.5 and 8.6-dev: 104 instructions, 11–104 executed per call, 3 branches. The work does not change between versions.
An instruction is not a fixed amount of time, so a matching count is not necessarily the same speed; what it rules out is a difference in the work itself.
Uses · 4
- did_action()Retrieves the number of times an action has been fired during the current request.
- wp_load_translations_early()Attempts an early load of translations.
- __()Retrieves the translation of $text.
- wpdb::bail()Wraps errors in a nice header and footer and dies.
Used by · 1
- wpdb::db_connect()Connects to and selects database.
Source code
public function select( $db, $dbh = null ) { if ( is_null( $dbh ) ) { $dbh = $this->dbh; } $success = mysqli_select_db( $dbh, $db ); if ( ! $success ) { $this->ready = false; if ( ! did_action( 'template_redirect' ) ) { wp_load_translations_early(); $message = '<h1>' . __( 'Cannot select database' ) . "</h1>\n"; $message .= '<p>' . sprintf( /* translators: %s: Database name. */ __( 'The database server could be connected to (which means your username and password is okay) but the %s database could not be selected.' ), '<code>' . htmlspecialchars( $db, ENT_QUOTES ) . '</code>' ) . "</p>\n"; $message .= "<ul>\n"; $message .= '<li>' . __( 'Are you sure it exists?' ) . "</li>\n"; $message .= '<li>' . sprintf( /* translators: 1: Database user, 2: Database name. */ __( 'Does the user %1$s have permission to use the %2$s database?' ), '<code>' . htmlspecialchars( $this->dbuser, ENT_QUOTES ) . '</code>', '<code>' . htmlspecialchars( $db, ENT_QUOTES ) . '</code>' ) . "</li>\n"; $message .= '<li>' . sprintf( /* translators: %s: Database name. */ __( 'On some systems the name of your database is prefixed with your username, so it would be like <code>username_%1$s</code>. Could that be the problem?' ), htmlspecialchars( $db, ENT_QUOTES ) ) . "</li>\n"; $message .= "</ul>\n"; $message .= '<p>' . sprintf( /* translators: %s: Support forums URL. */ __( 'If you do not know how to set up a database you should <strong>contact your host</strong>. If all else fails you may find help at the <a href="%s">WordPress support forums</a>.' ), __( 'https://wordpress.org/support/forums/' ) ) . "</p>\n"; $this->bail( $message, 'db_select_fail' ); } } }Changelog
Introduced in 0.71. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
About this page
- Parsed data
- Generated from the wordpress-develop 7.0.4 tag, from
src/wp-includes/class-wpdb.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it. - Corrections
- Something wrong on this page? Report it and it gets fixed in the next regeneration.