WordPress at a glance
function is not described

wpdb::get_col() public WP 0.71

Retrieves one column from the database.

Executes a SQL query and returns the column from the SQL result. If the SQL result contains more than one column, the column specified is returned. If $query is null, the specified column from the previous SQL result is returned.

{} It's a method of the class: wpdb{}

No Hooks.

Return

Array. Database query result. Array indexed from 0 by SQL result row number.

Usage

global $wpdb;
$wpdb->get_col( $query, $x );
$query(string/null)
SQL query.
Default: previous query
$x(int)
Column to return. Indexed from 0.
Default: 0

Changelog

Since 0.71 Introduced.

Code of wpdb::get_col() WP 5.5.1

<?php
public function get_col( $query = null, $x = 0 ) {
	if ( $this->check_current_query && $this->check_safe_collation( $query ) ) {
		$this->check_current_query = false;
	}

	if ( $query ) {
		$this->query( $query );
	}

	$new_array = array();
	// Extract the column values.
	if ( $this->last_result ) {
		for ( $i = 0, $j = count( $this->last_result ); $i < $j; $i++ ) {
			$new_array[ $i ] = $this->get_var( null, $x, $i );
		}
	}
	return $new_array;
}