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

[n.pettik]

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

> 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.