Question

Is it possible to use if/else in SQL? If I have a table called supplier with columns: sid -> primary key, sname and city.

Then I wish to:

1. select sid from supplier where city="taipei" if not empty.
2. Or select sid from supplier where city="tainan"

Answer 1

Yes, you can. I don’t know about other DBMS but I have used such things in Microsot SQL Server in my Stored Procedure like this;

IF EXISTS
   (SELECT [sid] FROM [supplier]  WHERE [city]= "taipei")

select sid from supplier where city="taipei"  // your true condition query
ELSE
select sid from supplier where city="tainan"

In MySQL From this link, it turns out that is also possible. see;

IF EXISTS(SELECT * FROM tbl_name WHERE category_code ='some-category-code') THEN UPDATE tbl_name SET active='0' WHERE category_code = 'some-category-code' END IF