Question

Im trying to create a php script that queries a database based on filter input from users

So essentially i want

select * from table where parent_id = '$filter_value'

However i want to apply a default value to $filter_value which will take effect if the user doesnt specify any filters, and will pull up all possible results.

I tried using * but it didnt work…

Answer 1

Two ways:

1. Compare the value to NULL

   SELECT * 
   FROM table
   WHERE ($filter_value IS NULL OR parent_id = '$filter_value')
   

2. Dynamically create the SQL based on whether $filter_value contains a value. If it does not, your query should simply be:

   SELECT *
   FROM table