How to return a boolean value on SQL Select Statement?
I tried this code:
SELECT CAST(1 AS BIT) AS Expr1
FROM [User]
WHERE (UserID = 20070022)
And it only returns TRUE if the UserID exists on the table. I want it to return FALSE if the UserID doesn't exist on the table.
What you have there will return no row at all if the user doesn't exist. Here's what you need:
SELECT CASE WHEN EXISTS (
SELECT *
FROM [User]
WHERE UserID = 20070022
)
THEN CAST(1 AS BIT)
ELSE CAST(0 AS BIT) END
* is more idiomatic. See this question.
AS bool part is very important): CAST( CASE WHEN EXISTS ( SELECT * FROM mytable WHERE mytable.id = 1) THEN TRUE ELSE FALSE END AS bool) AS nameofmycolumnPossibly something along these lines:
SELECT CAST(CASE WHEN COUNT(*) > 0 THEN 1 ELSE 0 END AS BIT)
FROM dummy WHERE id = 1;
Given that commonly 1 = true and 0 = false, all you need to do is count the number of rows, and cast to a boolean.
Hence, your posted code only needs a COUNT() function added:
SELECT CAST(COUNT(1) AS BIT) AS Expr1
FROM [User]
WHERE (UserID = 20070022)
Exists( test is much faster than doing a Count(1) test on tables with large numbers of rows.
UserID is indexed (or is even the PK) surely you're going straight to the one unique row that exists (or not).Use 'Exists' which returns either 0 or 1.
The query will be like:
SELECT EXISTS(SELECT * FROM USER WHERE UserID = 20070022)
SELECT 1 be faster than SELECT * in this case?select CAST(COUNT(*) AS BIT) FROM [User] WHERE (UserID = 20070022)
If count(*) = 0 returns false. If count(*) > 0 returns true.
I do it like this:
SELECT 1 FROM [dbo].[User] WHERE UserID = 20070022
Seeing as a boolean can never be null (at least in .NET), it should default to false or you can set it to that yourself if it's defaulting true. However 1 = true, so null = false, and no extra syntax.
Note: I use Dapper as my micro orm, I'd imagine ADO should work the same.
For those of you who are interested in getting the value adding a custom column name, this worked for me:
CAST(
CASE WHEN EXISTS (
SELECT *
FROM mytable
WHERE mytable.id = 1
)
THEN TRUE
ELSE FALSE
END AS bool)
AS "nameOfMyColumn"
You can skip the double quotes from the column name in case you're not interested in keeping the case sensitivity of the name (in some clients).
I slightly tweaked @Chad's answer for this.
Notice another equivalent problem: Creating an SQL query that returns (1) if the condition is satisfied and an empty result otherwise. Notice that a solution to this problem is more general and can easily be used with the above answers to achieve the question that you asked. Since this problem is more general, I am proving its solution in addition to the beautiful solutions presented above to your problem.
SELECT DISTINCT 1 AS Expr1
FROM [User]
WHERE (UserID = 20070022)
DECLARE @isAvailable BIT = 0;
IF EXISTS(SELECT 1 FROM [User] WHERE (UserID = 20070022))
BEGIN
SET @isAvailable = 1
END
initially isAvailable boolean value is set to 0
SELECT WHEN CAST(1 AS BIT) THEN 'YES' END AS result-- results in an error i.e.CAST(1 AS BIT)is not the same logical TRUE.