[MDEV-10305] CAST(string_expr AS SIGNED) does not truncate huge numbers well - Jira

Implicit CAST from string to signed bigint truncates the number the to maximum possible 64-bit signed value:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a BIGINT);

INSERT INTO t1 VALUES ('99999999999999999999');

SELECT * FROM t1;

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

| a                   |

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

| 9223372036854775807 |

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

So does explicit CAST from DECIMAL to SIGNED:

SELECT CAST(99999999999999999999 AS SIGNED);

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

| CAST(99999999999999999999 AS SIGNED) |

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

|                  9223372036854775807 |

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

So does explicit CAST from DOUBLE to SIGNED:

SELECT CAST(99999999999999999999e0 AS SIGNED);

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

| CAST(99999999999999999999e0 AS SIGNED) |

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

|                    9223372036854775807 |

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

Explicit CAST from string to SIGNED works differently:

SELECT CAST('99999999999999999999' AS SIGNED);

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

| CAST('99999999999999999999' AS SIGNED) |

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

|                                     -1 |

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

This looks wrong. Explicit CAST from string to SIGNED should also return 9223372036854775807.

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