Postgresql serial serial#
CREATE TABLE posts ( id serial PRIMARY KEY, title text, content text ) The id serial PRIMAR KEY above does a few things for us. DBE-5111 Postgres sequence: display valuable information in database tree. Therefore, it comes in handy when declaring a primary key for our table. Which still leaves you with a sequence that is out-of-sync with the values in the table, but at least you were made aware of that. The serial data type allows us to generate unique integer numbers automatically. You can still force this, using the override system value option: insert into t2 (id) overriding system value values (1) So you can accidentally "forget" the sequence usage. Results in: ERROR: cannot insert into column "id" Detail: Column "id" is an identity column defined as GENERATED ALWAYS. With the second table however, insert into t2 (id) values (1) You will get an error because the sequence was not advanced by the first insert, and now tries to insert the value 1 again. If you run another insert into t1 default_values The underlying sequence and the values in the table are not in sync any more. Now when you run: insert into t1 (id) values (1)
One thing that this new syntax allows is to prevent an accidental override of the value.Ĭonsider the following tables: create table t1 (id serial primary key) create table t2 (id integer primary key generated always as identity) The underlying implementation is still based on a sequence, the definition now complies with the SQL standard. Additional types from the same family are SMALLSERIAL and BIGSERIAL.
When creating a new table using the SERIAL pseudo-type, a sequence is created. To be more compliant with the SQL standard, Postgres 10 introduced the syntax using generated as identity. PostgreSQL enables you to create a sequence that is similar to the IDENTITY property supported by Oracle 12c identity column feature. However that is not part of the SQL standard. Serial is the "old" implementation of auto-generated unique values that has been part of Postgres for ages.
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