October 6, 2016 · Mysql

Mysql conditional INSERTS

Every now again it's useful to have slightly more control over a MySQL insert than simply making it idempotent via the IGNORE keyword. For example;

INSERT IGNORE INTO foo (id, column_bar) values (1, 'aaa'),  (2, 'bbb');  

The IGNORE keyword will simply skip over any primary or unique key constraint violations, essentially making the above statement idempotent assuming a primary key on id.

However let us suppose we have a data set without a primary key or more precisely the data we want to insert has more complex conditional requirements. Unfortunately MySQL's INSERT statement does not directly allow for greater selectivity but the SELECT statement does allowing us to take advantage of the INSERT...SELECT... form.

INSERT INTO tmp_users VALUES ( ....... *default user list*)

INSERT INTO users SELECT * FROM tmp_users WHERE .... <conditional logic here>

-- Optional as temporary tables only exist for duration of session.
DROP TABLE tmp_users;  

Admittedly this is a contrived example where there would likely be a UNIQUE key on username which could be taken advantage of in the INSERT IGNORE... statement format. However this is simply to illustrate how more complex logic can be wrapped around an INSERT statement when needed without any supporting code or stored procedures.

See here for full documentation on Mysql INSERT statement.