Improve dealing with check constraints

[dbussink]

This fixes a number of issues for check constaints. First it allows parsing both DROP CONSTRAINT and DROP CHECK in the parser so we can correctly drop an existing constraint. This was missing so far and only a foreign key constraint could be dropped.

Secondly, we improve dealing with constraints in schemadiff as well. Normalization there needs to generate names for constraints much like how we generate names for keys as well.

We also need to teach the diffing logic then how to create the proper DROP statements instead of a DROP FOREIGN KEY for all constraints that get dropped.

Related Issue(s)

Part of #10203

Checklist

• "Backport me!" label has been added if this change should be backported
• Tests were added or are not required
• Documentation was added or is not required

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[dbussink]

There's one specific diffing optimization for check constraints that isn't implemented yet that I wanted to look at separately, which is for enabling / disabling the ENFORCED flag on an existing constraint which can be changed with an ALTER TABLE ALTER CONSTRAINT <name> [ENFORCED | NOT ENFORCED] DDL style statement.

[shlomi-noach]

is there a maxlength handling? We've seen in normal keys, that the name for key#2 and onwards is a 30 characters prefix, then padded with _2... etc.

[dbussink]

@shlomi-noach Not yet, but since you were looking at it for regular indexes, I was wondering if it makes more sense to do that together with that one?

Let me try this out though and see what it looks like.

[dbussink]

Oh, haha, I think we can ignore this case as MySQL errors on it?

mysql> create table Y3PbHeDlyEgHtCKXmLlt8mC6Oe07UadTl1o75KQmZ3eWWkpZQlKw6WN0dSBtXSEt (id int primary key, i int, foreign key (i) references parent(id));
ERROR 1059 (42000): Identifier name 'y3pbhedlyeghtckxmllt8mc6oe07uadtl1o75kqmz3ewwkpzqlkw6wn0dsbtxset_ibfk_1' is too long

So we'd fail to create the table with the normalized name in the same way then when running this against the underlying MySQL.

[shlomi-noach]

@dbussink sounds good.

[dbussink]

There's one specific diffing optimization for check constraints that isn't implemented yet that I wanted to look at separately, which is for enabling / disabling the ENFORCED flag on an existing constraint which can be changed with an ALTER TABLE ALTER CONSTRAINT <name> [ENFORCED | NOT ENFORCED] DDL style statement.

This is implemented in the follow up in #10269