In this example, the subquery returned NULL, therefore, the query returned all rows from the customer table. See the following example: SELECTĬode language: SQL (Structured Query Language) ( sql ) If the subquery returns NULL, EXISTS returns true. The following example returns customers have not made any payment that greater than 11. ![]() If the subquery returns one or more rows, the NOT EXISTS returns false. It means that if the subquery returns no row, the NOT EXISTS returns true. The NOT operator negates the result of the EXISTS operator. In this example, for each customer in the customer table, the subquery checks the payment table to find if that customer made at least one payment ( p.customer_id = c.customer_id) and the amount is greater than 11 ( amount > 11) B) NOT EXISTS example The following statement returns customers who have paid at least one rental with an amount greater than 11: SELECT first_name, We will use the following customerand payment tables in the sample database for the demonstration: A) Find customers who have at least one payment whose amount is greater than 11. Note that if the subquery returns NULL, the result of EXISTS is true. Therefore, columns that appear on the SELECT clause of the subquery are not important.įor this reason, the common coding convention is to write EXISTS in the following form: SELECT The result of EXISTS operator depends on whether any row returned by the subquery, and not on the row contents. The EXISTS operator is often used with the correlated subquery. In case the subquery returns no row, the result is of EXISTS is false. If the subquery returns at least one row, the result of EXISTS is true. The EXISTS accepts an argument which is a subquery. The following illustrates syntax of the EXISTS operator: EXISTS (subquery) The EXISTS operator is a boolean operator that tests for existence of rows in a subquery. Introduction to PostgreSQL EXISTS operator Summary: in this tutorial, you will learn how to use the PostgreSQL EXISTS operator to test for existence of rows in a subquery.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |