Tagged with "sql"

Fun MySQL fact of the day: Extra confusing

If, over the last few days, you've started EXPLAINing your queries more, I commend you: you're on the path to becoming a database query optimiser extraordinaire. You may have also identified that the Extra column isn't a singleton value. You may have even seen something weird like Using where; ... read more

Fun MySQL fact of the day: OR not

We started discussing secondary indices yesterday, and we considered how we might create two separate indices on our user table. We also started to build an understanding of when MySQL can and shouldn't use an index for a query, but we omitted one fun fact. ... read more

Fun MySQL fact of the day: IGNORE at your own peril

Yesterday, we saw how INSERT ... ON DUPLICATE KEY UPDATE can unknowingly result in not-completely-expected situations. To get around that, you may have thought to use INSERT IGNORE, instead. Often, INSERT IGNORE is used when attempting to insert a row that may already exist. The underlying expectation a ... read more


As developers, part of our job is ensuring system stability long after we are finished writing code. It is our responsibility to ensure the next developer in our place doesn't inherit a system littered with landmines and that our customers' data integrity and privacy is always a top priority. Today's ... read more

Fun MySQL fact of the day: a CHECKered past

A Check Constraint is a table constraint, described in SQL-89, that allows a database index to remain consistent based on a specified search criteria or expression. For example, we could ADD CONSTRAINT is_even_ck CHECK(my_int_col % 2 = 0) to ensure that the value of the my_int_col column in every row ... read more