MDEV-31975: UCASE(varchar_col)=... not handled for partition tables

Enable sargable casefolding rewrite when the column is a part of
partitioning expression.

mysql-test/main/sargable_casefold_part.result

+set
+@tmp_switch_sarg_casefold=@@optimizer_switch,
+optimizer_switch='sargable_casefold=on';
+create table t1 (
+s1 varchar(15) collate utf8mb3_bin,
+s2 varchar(15) collate utf8mb3_general_ci
+) partition by key (s2) partitions 4;
+insert into t1 values ('aa','aa'),('bb','bb');
+explain format=json select * from t1 where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "t1",
+      "partitions": ["p2"],
+      "access_type": "system",
+      "rows": 1,
+      "filtered": 100
+    }
+  }
+}
+explain format=json delete from t1 where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "delete": 1,
+      "table_name": "t1",
+      "partitions": ["p2"],
+      "access_type": "ALL",
+      "rows": 1,
+      "attached_condition": "t1.s2 = 'AA'"
+    }
+  }
+}
+explain format=json update t1 set s1='aaa' where upper(s2)='AA';
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "update": 1,
+      "table_name": "t1",
+      "partitions": ["p2"],
+      "access_type": "ALL",
+      "rows": 1,
+      "attached_condition": "t1.s2 = 'AA'"
+    }
+  }
+}
+drop table t1;
+set optimizer_switch=@tmp_switch_sarg_casefold;

mysql-test/main/sargable_casefold_part.test

+--source include/have_partition.inc
+#
+# MDEV-31975: UCASE(varchar_col)=... not handled for partition tables
+#
+
+set
+  @tmp_switch_sarg_casefold=@@optimizer_switch,
+  optimizer_switch='sargable_casefold=on';
+
+create table t1 (
+  s1 varchar(15) collate utf8mb3_bin,
+  s2 varchar(15) collate utf8mb3_general_ci
+) partition by key (s2) partitions 4;
+insert into t1 values ('aa','aa'),('bb','bb');
+
+explain format=json select * from t1 where upper(s2)='AA';
+explain format=json delete from t1 where upper(s2)='AA';
+explain format=json update t1 set s1='aaa' where upper(s2)='AA';
+
+drop table t1;
+
+set optimizer_switch=@tmp_switch_sarg_casefold;

sql/opt_rewrite_remove_casefold.cc

@@ -5,13 +5,15 @@
 #include "mariadb.h"
 #include "sql_priv.h"
 #include <m_ctype.h>
+#include "sql_partition.h"
 #include "sql_select.h"
 
 #include "opt_trace.h"
 
 /*
   @brief
-    Check if passed item is "UCASE(table.key_part_col)"
+    Check if passed item is "UCASE(table.colX)" where colX is either covered
+    by some index or is a part of partition expression.
 
   @return
      Argument of the UCASE if passed item matches
@@ -27,18 +29,30 @@ static Item* is_upper_key_col(Item *item)
     Item *arg_real= arg->real_item();
     if (arg_real->type() == Item::FIELD_ITEM)
     {
-      Item_field *item_field= (Item_field*)arg_real;
-      if ((item_field->field->flags & PART_KEY_FLAG) &&
-          dynamic_cast<const Type_handler_longstr*>(arg_real->type_handler()))
+      if (dynamic_cast<const Type_handler_longstr*>(arg_real->type_handler()))
       {
-        /*
-          Make sure COERCIBILITY(UPPER(col))=COERCIBILITY(col)
-        */
-        DBUG_ASSERT(arg->collation.derivation ==
-                    item_func->collation.derivation);
-
-        /* Return arg, not arg_real. Do not walk into Item_ref objects */
-        return arg;
+        Field *field= ((Item_field*)arg_real)->field;
+        bool appl= (field->flags & PART_KEY_FLAG);
+
+#ifdef WITH_PARTITION_STORAGE_ENGINE
+        partition_info *part_info;
+        if (!appl && ((part_info= field->table->part_info)))
+        {
+          appl= bitmap_is_set(&part_info->full_part_field_set,
+                              field->field_index);
+        }
+#endif
+        if (appl)
+        {
+          /*
+            Make sure COERCIBILITY(UPPER(col))=COERCIBILITY(col)
+          */
+          DBUG_ASSERT(arg->collation.derivation ==
+                      item_func->collation.derivation);
+
+          /* Return arg, not arg_real. Do not walk into Item_ref objects */
+          return arg;
+        }
       }
     }
   }