MDEV-14668 ADD PRIMARY KEY IF NOT EXISTS on composite key.

Check the name of the primary key to be 'PRIMARY'. Than
differs it from any implicit primary keys created by an engine.

mysql-test/r/alter_table.result

@@ -2225,3 +2225,26 @@ t1	CREATE TABLE `t1` (
   `b` int(11) DEFAULT NULL
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1
 DROP TABLE t1;
+#
+# MDEV-14668 ADD PRIMARY KEY IF NOT EXISTS on composite key
+#
+CREATE TABLE t1 (
+`ID` BIGINT(20) NOT NULL,
+`RANK` MEDIUMINT(4) NOT NULL,
+`CHECK_POINT` BIGINT(20) NOT NULL,
+UNIQUE INDEX `HORIZON_UIDX01` (`ID`, `RANK`)
+) ENGINE=InnoDB;
+ALTER TABLE t1 ADD PRIMARY KEY IF NOT EXISTS (`ID`, `CHECK_POINT`);
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `ID` bigint(20) NOT NULL,
+  `RANK` mediumint(4) NOT NULL,
+  `CHECK_POINT` bigint(20) NOT NULL,
+  PRIMARY KEY (`ID`,`CHECK_POINT`),
+  UNIQUE KEY `HORIZON_UIDX01` (`ID`,`RANK`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+ALTER TABLE t1 ADD PRIMARY KEY IF NOT EXISTS (`ID`, `CHECK_POINT`);
+Warnings:
+Note	1061	Multiple primary key defined
+DROP TABLE t1;

mysql-test/t/alter_table.test

@@ -1841,3 +1841,19 @@ CREATE TABLE t1 (a INT, b INT) ENGINE=InnoDB;
 ALTER TABLE t1 DROP INDEX IF EXISTS fk, DROP COLUMN IF EXISTS c;
 SHOW CREATE TABLE t1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-14668 ADD PRIMARY KEY IF NOT EXISTS on composite key
+--echo #
+CREATE TABLE t1 (
+        `ID` BIGINT(20) NOT NULL,
+            `RANK` MEDIUMINT(4) NOT NULL,
+                `CHECK_POINT` BIGINT(20) NOT NULL,
+                    UNIQUE INDEX `HORIZON_UIDX01` (`ID`, `RANK`)
+    ) ENGINE=InnoDB;
+
+ALTER TABLE t1 ADD PRIMARY KEY IF NOT EXISTS (`ID`, `CHECK_POINT`);
+SHOW CREATE TABLE t1;
+ALTER TABLE t1 ADD PRIMARY KEY IF NOT EXISTS (`ID`, `CHECK_POINT`);
+DROP TABLE t1;
+

sql/sql_table.cc

@@ -5930,7 +5930,9 @@ handle_if_exists_options(THD *thd, TABLE *table, Alter_info *alter_info)
 
       /* Check if the table already has a PRIMARY KEY */
       if (key->type == Key::PRIMARY &&
-          table->s->primary_key != MAX_KEY)
+          table->s->primary_key != MAX_KEY &&
+          (keyname=  table->s->key_info[table->s->primary_key].name) &&
+          my_strcasecmp(system_charset_info, keyname, primary_key_name) == 0)
       {
         push_warning_printf(thd, Sql_condition::WARN_LEVEL_NOTE,
             ER_DUP_KEYNAME, ER(ER_MULTIPLE_PRI_KEY));