Question

I got this piece of code from Mysql 4th edition to check table existence

SELECT * FROM table WHERE FALSE;

I cant quite under stand the where clause.
If im not mistaken there is no boolean type in mysql, so basically it been cast to

SELECT * FROM table WHERE 0;

And should it be a column on a where clause?

SELECT * FROM table WHERE column = false;

Any explaination greatly appreciated.

Answer 1

No it doesn’t have to have column as operand 🙂

When you open mysql select manual than expressions you would find there simple_expr what should mean conditions like WHERE 1 (about booleans) but I understand it can be confusing (and it’s rare to use conditions without columns).

When you do SELECT * FROM table WHERE FALSE; it’s basically this:

if there's table `table`
    return 0 rows (minimal database overhead) and valid resource
else
    return false

Just take a look on return values from mysql_query.