What does "WHERE 1" mean in SQL?

Question

Sometimes phpMyAdmin generates queries like:

SELECT *  FROM  `items`  WHERE 1  LIMIT 0 , 30 

I wonder if WHERE 1 has any meaning in a query like that.

Answer 1

It doesn't. It means ALWAYS TRUE so it won't have any filtering impact on your query. Query planner will probably ignore that clause.

It's usually used when you build a client side query by concatenating filtering conditions.

So, if your base query is stored in a string like this (example is in PHP, but it certainly applies to many other languages):

$sql = "select * from foo where 1 "; 

Then you can just concatenate a lot of filtering conditions with an AND clause regardless of it being the first condition you are using or not:

// pseudo php follows... if ($filter_by_name) {     $sql = $sql . " and name = ? "; } if ($filter_by_number) {     $sql = $sql . " and number = ? "; } // so on, and so forth.