Bug#25587256: NEWDD: FK: NEED TO SET PROPER REFERENCED COLUMN CASE

The problem was that the name of the columns referenced by
a foreign key was not converted to lower case when they
were stored in the data dictionary. This would have given
a change of behavior when the data dictionary eventually
is used for FK info in e.g. SHOW CREATE TABLE.
On current trunk, InnoDB's data dictionary is still used,
so this bug had no visible effects yet.

This patch fixes the problem by converting referenced column
names to lower case when they are stored in the data dictionary.

Author: jhauglid

mysql-test/r/dd_debug.result

@@ -223,4 +223,26 @@ Warnings:
 Note	1051	Unknown table 'test.t1'
 DROP TABLE t2;
 DROP VIEW v1;
+#
+# Bug#25587256 NEWDD: FK: NEED TO SET PROPER REFERENCED COLUMN CASE
+#
+CREATE TABLE t1 (pk INT PRIMARY KEY);
+CREATE TABLE t2 (fk INT, FOREIGN KEY (FK) REFERENCES t1 (PK));
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `fk` int(11) DEFAULT NULL,
+  KEY `fk` (`fk`),
+  CONSTRAINT `t2_ibfk_1` FOREIGN KEY (`fk`) REFERENCES `t1` (`pk`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+SET SESSION debug= '+d,skip_dd_table_access_check';
+SELECT foreign_key_column_usage.referenced_column_name
+FROM mysql.foreign_key_column_usage, mysql.foreign_keys, mysql.tables
+WHERE tables.name= 't2'
+AND tables.id = foreign_keys.table_id
+AND foreign_keys.id = foreign_key_column_usage.foreign_key_id;
+referenced_column_name
+pk
+SET SESSION debug= '-d,skip_dd_table_access_check';
+DROP TABLE t2, t1;
 ###################################################################

mysql-test/t/dd_debug.test

@@ -284,6 +284,25 @@ DROP TABLE IF EXISTS t1;
 DROP TABLE t2;
 DROP VIEW v1;
 
+--echo #
+--echo # Bug#25587256 NEWDD: FK: NEED TO SET PROPER REFERENCED COLUMN CASE
+--echo #
+
+CREATE TABLE t1 (pk INT PRIMARY KEY);
+CREATE TABLE t2 (fk INT, FOREIGN KEY (FK) REFERENCES t1 (PK));
+
+SHOW CREATE TABLE t2;
+SET SESSION debug= '+d,skip_dd_table_access_check';
+# Case should match SHOW CREATE TABLE output.
+SELECT foreign_key_column_usage.referenced_column_name
+FROM mysql.foreign_key_column_usage, mysql.foreign_keys, mysql.tables
+WHERE tables.name= 't2'
+AND tables.id = foreign_keys.table_id
+AND foreign_keys.id = foreign_key_column_usage.foreign_key_id;
+SET SESSION debug= '-d,skip_dd_table_access_check';
+
+DROP TABLE t2, t1;
+
 --echo ###################################################################
 
 --disable_connect_log

sql/sql_table.cc

@@ -5919,7 +5919,12 @@ static bool prepare_foreign_key(THD *thd,
       DBUG_RETURN(true);
     }
 
-    fk_info->fk_key_part[column_nr]= fk_col->field_name;
+    // Always store column names in lower case.
+    char buff[NAME_LEN + 1];
+    my_stpncpy(buff, fk_col->field_name.str, NAME_LEN);
+    my_casedn_str(system_charset_info, buff);
+    fk_info->fk_key_part[column_nr].str= sql_strdup(buff);
+    fk_info->fk_key_part[column_nr].length= strlen(buff);
   }
   DBUG_RETURN(false);
 }