Where not exists (select * from Test1 as t where t.key = v.key and t.value = v. Unless one or both of the "key"/"value" pair can be null. 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. 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. To return the row if it already exists with s as ( The syntax of the RETURNING list is identical to that of the output list of SELECT. Read the detailed explanation over there and pick the approach that best fits your use case.Yes there is returning INSERT INTO tag ("key", "value") Especially if the row frequently already exists, this is a bit faster. Here the TRUE value is always illustrated with numeric value 1, and the FALSE value is denoted as. In other words, we can say that: If a subquery returns any record, the Exists condition will return a TRUE value, or else, it will return a FALSE. 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 Wiki page was only maintained until a few weeks before commit, where the patch further evolved in some minor aspects (most notably, the syntax became ON CONFLICT DO UPDATE/NOTHING). The PostgreSQL EXISTS condition is a type of Boolean operator which returns the true or false result. EXISTS EXISTS ( subquery ) The argument of EXISTS is an arbitrary SELECT statement, or subquery. The patch has been committed 1, and will appear in PostgreSQL 9.5. So here the overhead is slightly smaller (simpler queries), but the time frame for a race condition is slightly bigger. This feature is popularly known as 'UPSERT'. The alternative with CTEs runs as one SQL statement. This is assuming a UNIQUE constraint (or a UNIQUE index) on email, obviously. 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. 4 Answers Sorted by: 72 You can use an outer join against a values list (similar to Martin's answer mentioned above): select t.id from ( values (4), (5), (6) ) as t (id) left join images i on i.id t.id where i. RAISE NOTICE 'It actually happened!' - hardly ever happensĮXIT WHEN email_id IS NOT NULL - else keep looping 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). RETURNING mailing_list.email_id INTO email_id ĮXCEPTION WHEN UNIQUE_VIOLATION THEN - inserted in concurrent session. INSERT INTO mailing_list (email) VALUES (_email) When create a table, it's possible to use IF NOT EXISTS syntax. SELECT INTO email_id m.email_id FROM mailing_list m WHERE m.email = _email 1 I have a record: insert into posts (id, title, body) values (1, 'First post', 'Awesome') If the First post title and Awesome body already exist in the db, I want to ignore it. 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: Already explained how to avoid the error message you saw.
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