SQL中的IF / ELSE语句

Question

My SQL statement:

select * 
from categories 
where onair = 1 and City LIKE 's%';

First part:

select * 
from categories 
where onair = 1

second part:

and city like 's%';

If city column is not null , then I want to execute second part too. Otherwise, execute only first part.

Answer 1

You can create this behavior by a combination of the logical and and or operators:

SELECT *
FROM   categories
WHERE  onair = 1 AND (city IS NULL OR city LIKE 's%');

Answer 2

The case statement is your friend...

select *, 
case when City like 's%' then City
else '' end as City 
from categories where onair=1

That will only return City if it is like 's%'. Otherwise, it will return blank. Your other criteria is safely separate..