Is this the proper way to do boolean test in SQL?

Assume active is a "boolean field" (tiny int, with 0 or 1)

-- Find all active users select * from users where active -- Find all inactive users select * from users where NOT active 

In words, can the "NOT" operator be applied directly on the boolean field?

7 Answers

A boolean in SQL is a bit field. This means either 1 or 0. The correct syntax is:

select * from users where active = 1 /* All Active Users */ 

or

select * from users where active = 0 /* All Inactive Users */ 

With Postgres, you may use

select * from users where active 

or

select * from users where active = 't' 

If you want to use integer value, you have to consider it as a string. You can't use integer value.

select * from users where active = 1 -- Does not work select * from users where active = '1' -- Works 

MS SQL 2008 can also use the string version of true or false...

select * from users where active = 'true' -- or -- select * from users where active = 'false' 

In SQL Server you would generally use. I don't know about other database engines.

select * from users where active = 0 

I personally prefer using char(1) with values 'Y' and 'N' for databases that don't have a native type for boolean. Letters are more user frendly than numbers which assume that those reading it will now that 1 corresponds to true and 0 corresponds to false.

'Y' and 'N' also maps nicely when using (N)Hibernate.

PostgreSQL supports boolean types, so your SQL query would work perfectly in PostgreSQL.

If u r using SQLite3 beware:

It takes only 't' or 'f'. Not 1 or 0. Not TRUE OR FALSE.

Just learned the hard way.