WPDB: When deciding if a query needs extra sanity checking based on collation, we can quickly return if it's a query that will never return user data.

Fixes #32029.


Built from https://develop.svn.wordpress.org/trunk@32232


git-svn-id: http://core.svn.wordpress.org/trunk@32206 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-RC2-32231';
+$wp_version = '4.2-RC2-32232';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/wp-db.php

@@ -2399,20 +2399,32 @@ class wpdb {
 			return true;
 		}
 
+		// We don't need to check the collation for queries that don't read data.
+		$query = ltrim( $query, "\r\n\t (" );
+		if ( preg_match( '/^(?:SHOW|DESCRIBE|DESC|EXPLAIN)\s/i', $query ) ) {
+			return true;
+		}
+
 		$table = $this->get_table_from_query( $query );
 		if ( ! $table ) {
 			return false;
 		}
 
 		$this->checking_collation = true;
-		$this->get_table_charset( $table );
+		$collation = $this->get_table_charset( $table );
 		$this->checking_collation = false;
 
+		// Tables with no collation, or latin1 only, don't need extra checking.
+		if ( false === $collation || 'latin1' === $collation ) {
+			return true;
+		}
+
 		$table = strtolower( $table );
 		if ( empty( $this->col_meta[ $table ] ) ) {
 			return false;
 		}
 
+		// If any of the columns don't have one of these collations, it needs more sanity checking.
 		foreach( $this->col_meta[ $table ] as $col ) {
 			if ( empty( $col->Collation ) ) {
 				continue;