[MDEV-8466] CAST works differently for DECIMAL/INT vs DOUBLE for empty strings - Jira

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DECIMAL/INT vs DOUBLE work differently on CAST for empty strings:

SET sql_mode='STRICT_ALL_TABLES';

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a INT);

INSERT INTO t1 VALUES (CAST('' AS INT));

and

SET sql_mode='STRICT_ALL_TABLES';

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a DECIMAL);

INSERT INTO t1 VALUES (CAST('' AS DECIMAL));

correctly return

ERROR 1292 (22007): Truncated incorrect DECIMAL value: ''

DOUBLE works differently:

SET sql_mode='STRICT_ALL_TABLES';

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a DOUBLE);

INSERT INTO t1 VALUES (CAST('' AS DOUBLE));

It accepts the value silently:

Query OK, 1 row affected (0.03 sec)

This happens because the CAST alone does not produce any warnings for DOUBLE:

SELECT CAST('' AS DOUBLE);

and produces a warning for DECIMAL and INT:

MariaDB [test]> SELECT CAST('' AS INT);

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

| CAST('' AS INT) |

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

|               0 |

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

1 row in set, 1 warning (0.00 sec)

MariaDB [test]> SELECT CAST('' AS INT);

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

| CAST('' AS INT) |

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

|               0 |

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

1 row in set, 1 warning (0.00 sec)

MariaDB [test]> SHOW WARNINGS;

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

| Level   | Code | Message                               |

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

| Warning | 1292 | Truncated incorrect INTEGER value: '' |

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

1 row in set (0.00 sec)

During a discussion on maria-developers, Sergei and Bar agreed that a warning should be generated for all numeric data types.

relates to

MDEV-8109 unexpected CAST result

MDEV-8300 CAST('' AS DECIMAL) is too strict on INSERT in strict mode

MDEV-8468 CAST and INSERT work differently for DECIMAL/INT vs DOUBLE for a string with trailing spaces

MDEV-8806 Numeric CAST produce different warnings for strings literals vs functions

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