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

[n.pettik]

> On 27 Mar 2019, at 17:03, Vladislav Shpilevoy <v.shpilevoy at tarantool.org> wrote:
> 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.

Thank you for your feedback. I’m going to send rebased version of
top-most patches soon.

>>> 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.

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