Showing posts from June, 2018

How many times does my table function execute?

A left correlation join occurs when you pass as an argument to your table function a column value from a table or view referenced to the left in the table clause. This technique is used with XMLTABLE and JSON_TABLE built-in functions, but also applies to your own table functions.

Here's the thing to remember:
The table function will be called for each row in the table/view that is providing the column to the function.  Clearly, this could cause some performance issues, so be sure that is what you want and need to do.

The following code demonstrates this behavior, for both pipelined and non-pipelined functions.

CREATE TABLE things ( thing_id NUMBER, thing_name VARCHAR2 (100) ) / BEGIN INSERT INTO things VALUES (1, 'Thing 1'); INSERT INTO things VALUES (2, 'Thing 2'); COMMIT; END; / CREATE OR REPLACE TYPE numbers_t IS TABLE OF NUMBER / CREATE OR REPLACE FUNCTION more_numbers (id_in IN NUMBER) RETURN numbers_t IS l_numbers numbers_t := …