[tarantool-patches] Re: [PATCH v2 1/5] sql: introduce structs assembling DDL arguments during parsing

[Vladislav Shpilevoy]

On 27/03/2019 16:44, n.pettik wrote:
> 
>> On 27 Mar 2019, at 16:29, Vladislav Shpilevoy <v.shpilevoy at tarantool.org> wrote:
>> On 27/03/2019 16:00, n.pettik wrote:
>>>
>>>> On 26 Mar 2019, at 21:06, Vladislav Shpilevoy <v.shpilevoy at tarantool.org> wrote:
>>>>
>>>> Thanks for the fixes! This commit LGTM.
>>>> Lets proceed to the next patches, and start
>>>> with a rebase, which is going to be hard.
>>>
>>> Ok. Then I would like to clarify some details to avoid wasting time.
>>> In previous patch version, I used next (reworked) grammar to add
>>> FK constraints using ALTER:
>>>
>>> cmd ::= alter_table_start alter_table_action .
>>>
>>> alter_table_start ::= ALTER TABLE fullname(Z) . (1)
>>>
>>> alter_table_action ::= add_constraint_def.
>>> alter_table_action ::= drop_constraint_def.
>>> alter_table_action ::= rename.
>>>
>>> add_constraint_def ::= add_constraint_start constraint_def.
>>>
>>> add_constraint_start(N) ::= ADD CONSTRAINT nm(Z). (2)
>>> constraint_def ::= foreign_key_def.
>>>
>>> foreign_key_def ::= FOREIGN KEY LP eidlist(FA) RP REFERENCES nm(T)
>>>                       eidlist_opt(TA) matcharg(M) refargs(R) defer_subclause_opt(D).
>>>
>>> Now obviously I can’t use it since foreign_key_def should call
>>> create_fk_def_init() which in turn requires table name and name
>>> of constraint defined in rules (1) and (2).
>>>
>>> Why I want to use grammar mentioned above: it allows to remove
>>> code duplication. Rules to parse constraints are defined three times:
>>>
>>> 1. ccons rule - that is part of column definition: …, a INT REFERENCES t1);
>>> 2. tcons rule - that is part of CREATE TABLE: …, CONSTRAINT c FOREIGN KEY …);
>>> 3. ALTER TABLE statement
>>>
>>> All of them use the same grammar to parse statement starting from
>>> REFERENCES keyword. The same applies to UNIQUE and CHECK
>>> constraints. 
>>>
>>> IDK how to avoid using alter_entity_def_init() and create_constraint_def_init()
>>> and at the same time divide constraint definition into several stages.
>>>
>>> Ofc, we can still use simple approach like:
>>>
>>> cmd ::= ALTER TABLE fullname(Z) ADD CONSTRAINT nm(Z)  FOREIGN KEY
>>>             LP eidlist(FA) RP REFERENCES nm(T) eidlist_opt(TA) matcharg(M)
>>>             refargs(R) defer_subclause_opt(D)
>>>
>>> cmd ::= ALTER TABLE fullname(Z) ADD CONSTRAINT nm(Z)  UNIQUE
>>>             LP sortlist(X) RP
>>>
>>> cmd ::= ALTER TABLE fullname(Z) ADD CONSTRAINT nm(Z)  PRIMARY KEY
>>>             LP sortlist(X) RP
>>>
>>> cmd ::= ALTER TABLE fullname(Z) ADD CONSTRAINT nm(Z) CHECK …
>>>
>>> cmd ::= ALTER TABLE fullname(Z) RENAME TO nm(N) .
>>>
>>> Is this OK?
>>>
>>
>> Obviously, it is not. Why can't you define this?
>>
>> alter_table_start(T) ::= ALTER TABLE fullname(T)
>> alter_add_constraint(T, N) ::= alter_table_start(T) ADD CONSTRAINT nm(N).
> 
> Lemon can’t use two aliases as rule parameters at the same time.
> Instead we can introduce *another one* local struct to hold these names.

Yes, you can define a structure in parse.y to store these two parameters,
and unpack it back inside the concrete rules. It means, that such a
helper struct will never be stored anywhere out of parse.y.

> Anyway my initial worry was not about duplication of ALTER TABLE CREATE CONSTRAINT,
> but rather of constraints grammar (i.e. starting from FOREIGN KEY…).

For constraints grammar you can consult the standard. I do not remember
how it defines FOREIGN KEY rules, if it does at all. Personally for me
it looks ok.

> 
>> cmd ::= alter_add_constraint(T, N) FOREIGN KEY ...
>> cmd ::= alter_add_constraint(T, N) UNIQUE LP sortlist(X) RP
>> cmd ::= alter_add_constraint(T, N) PRIMARY KEY LP sortlist(X) RP
>> cmd ::= alter_add_constraint(T, N) CHECK ...
>> cmd ::= alter_table_start RENAME TO nm(N) .
>>
>> Then inside each cmd you have both table and constraint names.
>