![]() ![]() However, an index defined asĬREATE INDEX tab_x_y ON tab(x) INCLUDE (y) Ĭould handle these queries as index-only scans, because y can be The traditional approach to speeding up such queries would be toĬreate an index on x only. If we execute each statement of ** Block 2 **, each sentence separately, no error is generated to the INSERT since it does not validate but the final COMMIT is executed where it finds an inconsistency.Postgres docs state the following about Index-Only Scans and Covering-Indexes: Finally we created the CONSTRAINT DEFERRED do the following: **Bloque 3**ĭROP CONSTRAINT unique_div_nkit RESTRICT Here SI allows changing the primary key since it executes the entire first complete sentence (1328 rows) but although it is in transaction (BEGIN), the CONSTRAINT is validated immediately upon finishing each sentence without having made COMMIT, therefore generates the error when executing the INSERT. ![]() «unique_div_nkit» DETAIL: Ya existe la llave (div_nkit)=(1338). Ms) ERROR: llave duplicada viola restricción de unicidad Query OK, 1328 rows affected (execution time: 858 ms total time: 858 Query OK, 0 rows affected (execution time: 0 ms total time: 0 ms) INSERT INTO public.ele_kitscompletos(div_nkit, otro_campo) UPDATE ele_kitscompletos set div_nkit = div_nkit + 1 The CONSTRAINT IMMEDIATE is now created and each statement is executed separately: ALTER TABLE ele_kitscompletos In Postgres, executing an UPDATE for each ROW verifies that the RESTRICTION or CONSTRAINT is met. This creates a default primary key NOT DEFERRED for the table so when trying the next UPDATE we get error: update ele_kitscompletosĮRROR: duplicate key violates uniqueness restriction ![]() The following constraint was added to a table of 1337 records, where the kit is the primary key: **Bloque 1** Uses less space (same way as a partial index) and is deferrable: ALTER TABLE bookingĪlthough the years of this question have passed, I would like to clarify for Spanish speakers, the tests have been done in Postgres: These two combined make the constraint act as a filtered unique index.īut it's a constraint and EXCLUDE constraints can be deferred.Īn improvement of the above method (thnx to Denis Ryzhkov) is to use a partial (filtered) EXCLUDE constraint. So it acts as a filtered index with WHERE booking_status = 1.Īll the WITH operators are = so it acts as a UNIQUE constraint. Unique and exclude constraints accept rows where one or more of the expressions is NULL. We could write (CASE WHEN booking_status = 1 THEN TRUE END) as (booking_status = 1 OR NULL) if that makes it any more clear. The CASE expression becomes NULL when booking_status is null or different than 1. (CASE WHEN booking_status = 1 THEN TRUE END) WITH = With this design and assuming that booking_status has only 2 possible options (0 and 1), you could remove it entirely from booking (if there is a row at booking_status, it's 1, if not is 0).Īnother method would be to (ab)use an EXCLUDE constraint: ALTER TABLE booking REFERENCES public.booking (booking_id, check_in, check_out) Something like this: CREATE TABLE public.booking_statusįOREIGN KEY (booking_id, check_in, check_out) What you could do, if you want to implement this constraint as deferrable, is to add one more table in the design. So the unique partial index (and the implicit constraint it implements) will be checked at every statement (and in fact after every row insert/update in current implementation), not at the end of transaction. Other types of constraints ( FOREIGN KEY, PRIMARY KEY, EXCLUDE) are also deferrable - but not CHECK constraints. A index cannot be deferred - doesn't matter if it is UNIQUE or not, partial or not, only a UNIQUE constraint. ![]()
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