![]() ![]() Read the detailed explanation over there and pick the approach that best fits your use case. Especially if the row frequently already exists, this is a bit faster. So here the overhead is slightly smaller (simpler queries), but the time frame for a race condition is slightly bigger. The alternative with CTEs runs as one SQL statement. If it returns at least one row, the result of EXISTS is true if the subquery returns no rows, the result of EXISTS is false. The subquery is evaluated to determine whether it returns any rows. This is assuming a UNIQUE constraint (or a UNIQUE index) on email, obviously. To generate a ID value, you can omit the SERIAL column in INSERT statement, or specify DEFAULT keyword: - Omit serial column INSERT INTO teams ( name) VALUES ('Aston Villa') - Specify DEFAULT INSERT INTO teams VALUES (DEFAULT, 'Manchester City') Note that you cannot insert NULL, but can insert 0. EXISTS EXISTS ( subquery ) The argument of EXISTS is an arbitrary SELECT statement, or subquery. You only need the loop to deal with a possible race condition: If a concurrent transaction writes the same email value in between SELECT and INSERT, you would get a unique violation - which is handled properly here. RAISE NOTICE 'It actually happened!' - hardly ever happensĮXIT WHEN email_id IS NOT NULL - else keep looping RETURNING mailing_list.email_id INTO email_id ĮXCEPTION WHEN UNIQUE_VIOLATION THEN - inserted in concurrent session. To use the upsert feature in PostgreSQL, you use the INSERT ON CONFLICT statement as follows: INSERT INTO tablename (columnlist) VALUES (valuelist) ON CONFLICT target action Code language: SQL (Structured Query Language) (sql) PostgreSQL added the ON CONFLICT target action clause to the INSERT statement to support the upsert feature. ![]() INSERT INTO mailing_list (email) VALUES (_email) SELECT INTO email_id m.email_id FROM mailing_list m WHERE m.email = _email ![]() Is SELECT or INSERT in a function prone to race conditions?ĬREATE OR REPLACE FUNCTION f_email_insel(_email text, OUT email_id int) ASīEGIN - start inner block inside loop to handle possible exception.Here is a simple variant of the related version we have been referring to: So alternatively, you can use the subquery to check the existence of a specific record in a table. Where not exists (select * from Test1 as t where t.key = v.key and t.value = v.Already explained how to avoid the error message you saw. In PostgreSQL, the INSERT statement doesn’t support the IF NOT EXISTS option. Unless one or both of the "key"/"value" pair can be null. WHERE clause condition was not satisfied, the row will not be returned. For example, if a row was locked but not updated because an ON CONFLICT DO UPDATE. Only rows that were successfully inserted or updated will be returned. If the row does not exist it will return the inserted one else the existing one.īTW, if the pair "key"/"value" makes it unique then it is the primary key, and there is no need for an id column. It's based on Common Table Expressions (CTEs) and that fact that with PostgreSQL, you can perform not only SELECTs, but also INSERTs, UPDATEs and DELETEs (see here also). The syntax of the RETURNING list is identical to that of the output list of SELECT. I got: query has no destination for result data Sqlfiddle postgresql postgresql-9. To return the row if it already exists with s as ( BEGIN LOCK TABLE mailinglist IN SHARE ROW EXCLUSIVE MODE INSERT INTO mailinglist (email) SELECT 'email' WHERE NOT EXISTS ( SELECT FROM mailinglist WHERE email'email' ) COMMIT I have tried adding the returning id but it doesn't work. Yes there is returning INSERT INTO tag ("key", "value") ![]()
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