From 3f7bc21548bedb76054076b25becc983d40d76cc Mon Sep 17 00:00:00 2001
From: Boone Gorges <boonebgorges@gmail.com>
Date: Wed, 13 Sep 2017 14:48:45 +0000
Subject: [PATCH] Taxonomy: Force a `DISTINCT` term query when result count
 matters.

Generally, duplicate terms returned by a term query are eliminated in PHP,
after the database query takes place. This technique doesn't work properly
when the query parameters specify the `number` of results, since the results
of a `SELECT ... LIMIT x...` query may be deduplicated to a count less than
`x`. In these cases, we force the original query to be `DISTINCT`.

Props elvishp2006.
Fixes #41796.
Built from https://develop.svn.wordpress.org/trunk@41377


git-svn-id: http://core.svn.wordpress.org/trunk@41210 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/class-wp-term-query.php | 15 +++++++++++++--
 wp-includes/version.php             |  2 +-
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/wp-includes/class-wp-term-query.php b/wp-includes/class-wp-term-query.php
index 12e7dec242..f6f53f210c 100644
--- a/wp-includes/class-wp-term-query.php
+++ b/wp-includes/class-wp-term-query.php
@@ -551,6 +551,16 @@ class WP_Term_Query {
 			$limits = '';
 		}
 
+		$do_distinct = false;
+
+		/*
+		 * Duplicate terms are generally removed when necessary after the database query.
+		 * But when a LIMIT clause is included in the query, we let MySQL enforce
+		 * distinctness so the count is correct.
+		 */
+		if ( ! empty( $limits ) && 'all_with_object_id' !== $args['fields'] ) {
+			$do_distinct = true;
+		}
 
 		if ( ! empty( $args['search'] ) ) {
 			$this->sql_clauses['where']['search'] = $this->get_search_sql( $args['search'] );
@@ -568,8 +578,7 @@ class WP_Term_Query {
 		if ( ! empty( $meta_clauses ) ) {
 			$join .= $mq_sql['join'];
 			$this->sql_clauses['where']['meta_query'] = preg_replace( '/^\s*AND\s*/', '', $mq_sql['where'] );
-			$distinct .= "DISTINCT";
-
+			$do_distinct = true;
 		}
 
 		$selects = array();
@@ -631,6 +640,8 @@ class WP_Term_Query {
 
 		$where = implode( ' AND ', $this->sql_clauses['where'] );
 
+		$distinct = $do_distinct ? 'DISTINCT' : '';
+
 		/**
 		 * Filters the terms query SQL clauses.
 		 *
diff --git a/wp-includes/version.php b/wp-includes/version.php
index ad11c3615e..79383f07fc 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9-alpha-41376';
+$wp_version = '4.9-alpha-41377';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.