[MDEV-8222] "string_field LIKE int_const" returns a wrong result in case of UCS2 - Jira

This script:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a VARCHAR(10) CHARSET utf8);

INSERT INTO t1 VALUES ('1');

SELECT * FROM t1 WHERE a LIKE 1;

correctly returns one row:

+------+

| a    |

+------+

| 1    |

+------+

If I change character set from utf8 to ucs2, it returns empty set:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a VARCHAR(10) CHARSET ucs2);

INSERT INTO t1 VALUES ('1');

SELECT * FROM t1 WHERE a LIKE 1;

The problem happens in this piece of the code:

bool Item_func::setup_args_and_comparator(THD *thd, Arg_comparator *cmp)

  DBUG_ASSERT(arg_count == 2);

  if (args[0]->cmp_type() == STRING_RESULT &&

      args[1]->cmp_type() == STRING_RESULT &&

      agg_arg_charsets_for_comparison(cmp->cmp_collation, args, 2))

      return true;

In case of LIKE it should unconditionally call arg_arg_charsets_for_comparison(), no matter that cmp_type() of the arguments are.

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