Bug #119467 Creating the index directly works, but the operation fails when wrapped in an IF() function,

• Submitted: 27 Nov 6:05
• Reporter: Go Yakult
• Status: Open
• Category: MySQL Server: DDL
• Severity: S2 (Serious)
• Version: 8.0.41
• OS: Any
• CPU Architecture: Any

[27 Nov 6:05] Go Yakult

Description:
Creating the index directly works, but the operation fails when wrapped in an IF() function, and the resulting error message is not correct or is misleading.

mysql> CREATE UNIQUE INDEX i1 ON t0(c3);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP INDEX i1 ON t0;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> CREATE UNIQUE INDEX i1 ON t0(c2);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP INDEX i1 ON t0;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> CREATE UNIQUE INDEX i1 ON t0((IF(NULL, c3, c2)));
ERROR 1170 (42000): BLOB/TEXT column '!hidden!i1!0!0' used in key specification without a key length

How to repeat:
DROP TABLE IF EXISTS `t0`;
CREATE TABLE `t0` (
  `c0` decimal(10,0) DEFAULT NULL,
  `c1` tinyint(1) NOT NULL ,
  `c2` tinyint(1)  DEFAULT NULL,
  `c3` float(36,25) unsigned zerofill  DEFAULT NULL ,
  `c4` blob,
  `c5` float unsigned zerofill  DEFAULT NULL ,
  `c6` bigint(90) unsigned zerofill DEFAULT NULL ,
  `c7` smallint(14) unsigned zerofill  DEFAULT NULL ,
  `c8` tinyint(236) unsigned zerofill   DEFAULT NULL,
  `c9` mediumblob ,
  PRIMARY KEY (`c1`),
  KEY `i0` (`c1`,`c2`,`c4`(4),`c6`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

CREATE UNIQUE INDEX i1 ON t0(c3);
DROP INDEX i1 ON t0;
CREATE UNIQUE INDEX i1 ON t0(c2);
DROP INDEX i1 ON t0;
CREATE UNIQUE INDEX i1 ON t0((IF(NULL, c3, c2)));