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.