Source

File: wp-includes/wp-db.php

public function set_charset( $dbh, $charset = null, $collate = null ) {
		if ( ! isset( $charset ) ) {
			$charset = $this->charset;
		}
		if ( ! isset( $collate ) ) {
			$collate = $this->collate;
		}
		if ( $this->has_cap( 'collation' ) && ! empty( $charset ) ) {
			$set_charset_succeeded = true;

			if ( $this->use_mysqli ) {
				if ( function_exists( 'mysqli_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
					$set_charset_succeeded = mysqli_set_charset( $dbh, $charset );
				}

				if ( $set_charset_succeeded ) {
					$query = $this->prepare( 'SET NAMES %s', $charset );
					if ( ! empty( $collate ) ) {
						$query .= $this->prepare( ' COLLATE %s', $collate );
					}
					mysqli_query( $dbh, $query );
				}
			} else {
				if ( function_exists( 'mysql_set_charset' ) && $this->has_cap( 'set_charset' ) ) {
					$set_charset_succeeded = mysql_set_charset( $charset, $dbh );
				}
				if ( $set_charset_succeeded ) {
					$query = $this->prepare( 'SET NAMES %s', $charset );
					if ( ! empty( $collate ) ) {
						$query .= $this->prepare( ' COLLATE %s', $collate );
					}
					mysql_query( $query, $dbh );
				}
			}
		}
	}