Add more tests for CHECK constraints

[morgo]

CHECK constraints have a schema-level namespace, so (using an example roughly from the MySQL manual) this will fail:

DROP TABLE IF EXISTS t1, _t1_new;
CREATE TABLE t1 (
  id INT NOT NULL PRIMARY KEY auto_increment,
  CHECK (c1 <> c2),
  c1 INT CHECK (c1 > 10),
  c2 INT CONSTRAINT c2_positive CHECK (c2 > 0),
  c3 INT CHECK (c3 < 100),
  CONSTRAINT c1_nonzero CHECK (c1 <> 0),
  CHECK (c1 > c3)
);
CREATE TABLE _t1_new (
  id INT NOT NULL PRIMARY KEY auto_increment,
  CHECK (c1 <> c2),
  c1 INT CHECK (c1 > 10),
  c2 INT CONSTRAINT c2_positive CHECK (c2 > 0),
  c3 INT CHECK (c3 < 100),
  CONSTRAINT c1_nonzero CHECK (c1 <> 0),
  CHECK (c1 > c3)
);

..
ERROR 3822 (HY000): Duplicate check constraint name 'c2_positive'.

However, this doesn't fail in spirit. This is because to create the new table we use the following syntax:

DROP TABLE IF EXISTS t1, _t1_new;
CREATE TABLE t1 (
  id INT NOT NULL PRIMARY KEY auto_increment,
  CHECK (c1 <> c2),
  c1 INT CHECK (c1 > 10),
  c2 INT CONSTRAINT c2_positive CHECK (c2 > 0),
  c3 INT CHECK (c3 < 100),
  CONSTRAINT c1_nonzero CHECK (c1 <> 0),
  CHECK (c1 > c3)
);
CREATE TABLE _t1_new LIKE t1;
..
Query OK, 0 rows affected (0.01 sec)

This is because MySQL renames the constraints in CREATE TABLE.. LIKE:

mysql> SHOW CREATE TABLE _t1_new\G
*************************** 1. row ***************************
       Table: _t1_new
Create Table: CREATE TABLE `_t1_new` (
  `id` int NOT NULL AUTO_INCREMENT,
  `c1` int DEFAULT NULL,
  `c2` int DEFAULT NULL,
  `c3` int DEFAULT NULL,
  PRIMARY KEY (`id`),
  CONSTRAINT `_t1_new_chk_1` CHECK ((`c1` <> 0)),
  CONSTRAINT `_t1_new_chk_2` CHECK ((`c2` > 0)),
  CONSTRAINT `_t1_new_chk_3` CHECK ((`c1` <> `c2`)),
  CONSTRAINT `_t1_new_chk_4` CHECK ((`c1` > 10)),
  CONSTRAINT `_t1_new_chk_5` CHECK ((`c3` < 100)),
  CONSTRAINT `_t1_new_chk_6` CHECK ((`c1` > `c3`))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)

Since it's not guaranteed we will always use CREATE TABLE.. LIKE (although I see no reason to switch), we should have tests to ensure this case is handled correctly.