Fastest Check If Row Exists in Postgresql

Fastest check if row exists in PostgreSQL

Use the EXISTS key word for TRUE / FALSE return:

select exists(select 1 from contact where id=12)

Check if a row exists or not in postgresql

select
  case when exists (select true from table_name where table_column=?)
    then 'true'
    else 'false'
  end;

But it would be better to just return boolean instead of string:

select exists (select true from table_name where table_column=?);

PL/pgSQL checking if a row exists

Simpler, shorter, faster: EXISTS.

IF EXISTS (SELECT FROM people p WHERE p.person_id = my_person_id) THEN
  -- do something
END IF;

The query planner can stop at the first row found - as opposed to count(), which scans all (qualifying) rows regardless. Makes a big difference with big tables. The difference is small for a condition on a unique column: only one row qualifies and there is an index to look it up quickly.

Only the existence of at least one qualifying row matters. The SELECT list can be empty - in fact, that's shortest and cheapest. (Some other RDBMS don't allow an empty SELECT list on principal.)

^{Improved with @a_horse_with_no_name's comments.}

Efficient way to check if row exists for multiple records in postgres

You just want a left outer join:

SELECT 
   A.id as id, count(B.foreing_id) as cnt
FROM A
LEFT OUTER JOIN B ON
    A.id = B.foreing_id
GROUP BY A.id

failed to check if row with value exists In Postgres with Golang

Why not just a unique index on your users table?

CREATE UNIQUE INDEX unq_uuid ON users (uuid);

Then you don't have to check, you just try to insert and it will return an error if it already exists.

check if row exists with specific value

One simple solution uses aggregation:

SELECT
    t.taskid,
    t.name
FROM task t
INNER JOIN taskattributes ta
    ON t.taskid = ta.taskid
GROUP BY
    t.taskid,
    t.name
HAVING
    COUNT(CASE WHEN "key" = 'A' THEN 1 END) = 0;

If you are using Postgres 9.4 or later, you may use FILTER in the HAVING clause:

HAVING COUNT(*) FILTER (WHERE "key" = 'A') = 0

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