Question

I recently just fixed a bug in some of my code and was hoping someone could explain to me why the bug occurred.

I had a query like this:

SELECT * FROM my_table WHERE my_field=13

Unexpectedly, this was returning rows where my_field was equal to either 13 or 13a. The fix was simple, I changed the query to:

SELECT * FROM my_table WHERE my_field='13'

My question is, is this supposed to be the case? I’ve always thought that to return a similar field, you would use something like:

SELECT * FROM my_table WHERE my_field LIKE '13%'

What is the difference between LIKE + a Wild Card vs an equals operator with no quotes?

Answer 1

This statement returns rows for my_field = '13a':

SELECT * FROM my_table WHERE my_field=13

Because MySQL performs type conversion from string to number during the comparison, turning '13a' to 13. More on that in this documentation page.

Adding quotes turns the integer to a string, so MySQL only performs string comparison. Obviously, '13' cannot be equal to '13a'.

The LIKE clause always performs string comparison (unless either one of the operands is NULL, in which case the result is NULL).