Bug#20454533: Assertion failed: sargables == 0 || *keyfields ...

The fix for "regression from bug#19789450" had a problem for some
non-SELECT statements: These statements call st_select_lex::prepare()
after preparing some items specific to the UPDATE/DELETE operation,
so the prepare() call is clearing cond_count set for such references.
When a derived table is involved in the UPDATE, conditions counted in
the derived table are propagated to the outer query block. This happens
before cond_count is cleared in ::prepare().

The fix is to move the resetting of cond_count, etc from ::prepare()
to reinit_stmt_before_use(). Thus, the fields are reset by the
st_select_lex constructor for the first ::prepare(), for the
subsequent ::prepare()s, they are reset by reinit_stmt_before_use()

Author: roylyseng

mysql-test/r/update.result

@@ -625,3 +625,20 @@ id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered
 UPDATE t2, v1 AS t SET t2.b = t.a+5 ;
 DROP VIEW v1;
 DROP TABLE t1, t2;
+# Bug#20454533: Assertion failed: sargables == 0 || *keyfields ...
+CREATE TABLE t1(
+a int,
+c int,
+e int,
+f int,
+g blob,
+h int,
+i int,
+j blob,
+unique key (g(221),c),
+unique key (c,a,j(148)),
+key (i)
+) engine=innodb;
+UPDATE (SELECT 1 AS a FROM t1 NATURAL JOIN t1 AS t2) AS x, t1
+SET t1.e= x.a;
+DROP TABLE t1;

mysql-test/t/update.test

@@ -574,3 +574,23 @@ eval $query;
 DROP VIEW v1;
 DROP TABLE t1, t2;
 
+--echo # Bug#20454533: Assertion failed: sargables == 0 || *keyfields ...
+
+CREATE TABLE t1(
+ a int,
+ c int,
+ e int,
+ f int,
+ g blob,
+ h int,
+ i int,
+ j blob,
+ unique key (g(221),c),
+ unique key (c,a,j(148)),
+ key (i)
+) engine=innodb;
+
+UPDATE (SELECT 1 AS a FROM t1 NATURAL JOIN t1 AS t2) AS x, t1
+SET t1.e= x.a;
+
+DROP TABLE t1;

sql/sql_prepare.cc

@@ -2353,6 +2353,16 @@ void reinit_stmt_before_use(THD *thd, LEX *lex)
       /* see unique_table() */
       sl->exclude_from_table_unique_test= FALSE;
 
+      /*
+        These must be reset before every new preparation.
+        @note done here and not in st_select_lex::prepare() since for
+              multi-table UPDATE and DELETE, derived tables are merged into
+              the outer query block before ::prepare() is called.
+      */
+      sl->cond_count= 0;
+      sl->between_count= 0;
+      sl->max_equal_elems= 0;
+
       if (sl->where_cond())
       {
         DBUG_ASSERT(sl->where_cond()->real_item()); // no dangling 'ref'

sql/sql_resolver.cc

@@ -113,11 +113,6 @@ bool SELECT_LEX::prepare(THD *thd)
   Opt_trace_object trace_prepare(trace, "join_preparation");
   trace_prepare.add_select_number(select_number);
   Opt_trace_array trace_steps(trace, "steps");
-
-  // These must be reset before every condition preparation
-  cond_count= 0;
-  between_count= 0;
-  max_equal_elems= 0;
 
   // Initially, "all_fields" is the select list
   all_fields= fields_list;