Selecting all data from the related category

Dear Experts,

I use php and mysql database

I have a drop down list where my user filter my category to see the related items.

My sql sentence is like

Select * from catagory_table where catagory='$category' order by id

I want to add to my drop down list an "all" option.

How can i write an sql to bring all the data from category table if my user selects "all" as an option.

Do i need another a coloumn in the database? Or should i use and if statement for sql statement like:

If the user selects "all" as an option, use this sql sentence otherwise use this sql sentence?