Bug#36246859: Collation issue: ERROR 1253 (42000): COLLATION ''

              is not valid for CHARACTER SET

Condition pushdown to a view fails with a collation mismatch
if the view was created with a different charset than the
charset used when querying the view.
Problem is seen if the underlying fields in the view are
literals with COLLATE statements. The string literal with
the COLLATE statement is cloned when replacing expressions
in the condition that is being pushed down with the
expressions from the view. The string literal is currently
parsed with the connection charset which in this case is
different from the one that was used when the view was
created. Therefore the COLLATE statement fails.
Creation context for a view has the connection charset and
collation information which was used when the view
was created. This is currently used for parsing the view
when it is later queried. We use the same now when cloning
expressions from a view during condition pushdown.

Change-Id: Ib040b9a67ddedd5fb9bf5de6fafafb358226e9d9

Author: Chaithra Gopalareddy

mysql-test/r/derived_condition_pushdown.result

@@ -2429,6 +2429,16 @@ SELECT * FROM (SELECT * FROM v1 UNION SELECT * FROM v1) as dt
 WHERE field1 IN ('A');
 field1
 A
+EXPLAIN FORMAT=tree SELECT * FROM v1
+WHERE field1 IN ('C') OR
+COALESCE('A' COLLATE utf8mb4_spanish_ci IN ('B'), field1);
+EXPLAIN
+-> Zero rows (no matching row in const table)  (rows=0)
+
+SELECT * FROM v1
+WHERE field1 IN ('C') OR
+COALESCE('A' COLLATE utf8mb4_spanish_ci IN ('B'), field1);
+field1
 DROP VIEW v1;
 SET character_set_client = latin1;
 SET character_set_connection = latin1;

mysql-test/t/derived_condition_pushdown.test

@@ -1589,6 +1589,10 @@ SELECT 'B' COLLATE latin1_spanish_ci AS field1 FROM t1 AS t2;
 
 # Use a different charset now to query the view.
 SET character_set_connection = default;
+# Condition pushdown to view "v1" should happen
+# without any errors as it now uses the view's
+# connection context when "field1" is replaced
+# with "'A' COLLATE latin1_spanish_ci".
 let $query = SELECT * FROM v1 WHERE field1 IN ('C');
 --replace_regex $elide_costs
 --skip_if_hypergraph  # Depends on the query plan.
@@ -1600,6 +1604,17 @@ let $query = SELECT * FROM (SELECT * FROM v1 UNION SELECT * FROM v1) as dt
 --skip_if_hypergraph  # Depends on the query plan.
 eval EXPLAIN FORMAT=tree $query;
 eval $query;
+# view context of "v1" is not used when cloning the condition
+# "field1 IN ('C') OR COALESCE('A' COLLATE utf8mb4_spanish_ci IN ('B'), field1)"
+# to be pushed down in case of SET operations. It is used only when
+# "field1" is replaced with "'A' COLLATE latin1_spanish_ci".
+let $query = SELECT * FROM v1
+             WHERE field1 IN ('C') OR
+                   COALESCE('A' COLLATE utf8mb4_spanish_ci IN ('B'), field1);
+--replace_regex $elide_costs
+--skip_if_hypergraph  # Depends on the query plan.
+eval EXPLAIN FORMAT=tree $query;
+eval $query;
 DROP VIEW v1;
 
 #Simplified repro

sql/sql_derived.cc

@@ -606,6 +606,9 @@ bool copy_field_info(THD *thd, Item *orig_expr, Item *cloned_expr) {
   @param item           Item to be reparsed to get a clone.
   @param query_block    query block where expression is being parsed
   @param derived_table  derived table to which the item belongs to.
+                        "nullptr" when cloning to make a copy of the
+                        original condition to be pushed down
+                        to a derived table that has SET operations.
 
   @returns A copy of the original item (unresolved) on success else nullptr.
 */
@@ -678,8 +681,9 @@ static Item *parse_expression(THD *thd, Item *item, Query_block *query_block,
 
   // Get a newly created item from parser. Use the view creation
   // context if the item being parsed is part of a view.
-  const bool result =
-      parse_sql(thd, &parser_state, derived_table->view_creation_ctx);
+  View_creation_ctx *view_creation_ctx =
+      derived_table != nullptr ? derived_table->view_creation_ctx : nullptr;
+  const bool result = parse_sql(thd, &parser_state, view_creation_ctx);
 
   // If a statement is being re-prepared, then all the parameters
   // that are cloned above need to be synced with the original
@@ -1122,7 +1126,7 @@ bool Condition_pushdown::make_cond_for_derived() {
     if (derived_query_expression->is_set_operation()) {
       m_cond_to_push =
           derived_query_expression->outer_query_block()->clone_expression(
-              thd, orig_cond_to_push, m_derived_table);
+              thd, orig_cond_to_push, /*derived_table=*/nullptr);
       if (m_cond_to_push == nullptr) return true;
       m_cond_to_push->apply_is_true();
     }