[MDEV-9745] Crash with CASE WHEN TRUE THEN COALESCE(CAST(NULL AS UNSIGNED)) ELSE 4 END - Jira

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This script crashes the server:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 SELECT CASE WHEN TRUE THEN COALESCE(CAST(NULL AS UNSIGNED)) ELSE 4 END AS a;

The problem is not repeatable in MySQL-5.7.11.

It seems it's trying to create a DECIMAL(0,0) column. If I change the script slightly:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 SELECT CASE WHEN TRUE THEN COALESCE(CAST(NULL AS UNSIGNED)) ELSE 40 END AS a;

SHOW CREATE TABLE t1;

it does not crash, but the result is incorrect:

+-------+--------------------------------------------------------------------------------------------+

| Table | Create Table                                                                               |

+-------+--------------------------------------------------------------------------------------------+

| t1    | CREATE TABLE `t1` (

  `a` decimal(1,0) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

+-------+--------------------------------------------------------------------------------------------+

The field data type DECIMAL(1,0) is too small. It should probably be DECIMAL(2,0).

MySQL-5.7.11 creates a DECIMAL(2,0) column.

relates to

MDEV-9653 Assertion `length || !scale' failed in uint my_decimal_length_to_precision(uint, uint, bool)

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