In WP_Meta_Query, don't cast meta_value to CHAR.

`CHAR` is redundant, since the `meta_value` column is `LONGTEXT`. Meanwhile,
use of `CAST()` causes MySQL to ignore any index that the administrator may
have added to the column.

A number of automated tests were doing searches for `CAST` in the SQL strings
generated by `WP_Meta_Query` (for reasons unrelated to the `CAST()` behavior).
These tests have been updated to expect the new query format.

Props ericlewis.
Fixes #36625.
Built from https://develop.svn.wordpress.org/trunk@37594

Author: boonebgorges

wp-includes/class-wp-meta-query.php

@@ -632,7 +632,11 @@ public function get_sql_for_clause( &$clause, $parent_query, $clause_key = '' )
 			}
 
 			if ( $where ) {
-				$sql_chunks['where'][] = "CAST($alias.meta_value AS {$meta_type}) {$meta_compare} {$where}";
+				if ( 'CHAR' === $meta_type ) {
+					$sql_chunks['where'][] = "$alias.meta_value {$meta_compare} {$where}";
+				} else {
+					$sql_chunks['where'][] = "CAST($alias.meta_value AS {$meta_type}) {$meta_compare} {$where}";
+				}
 			}
 		}
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.6-alpha-37593';
+$wp_version = '4.6-alpha-37594';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.