열의 내용에 따라 T-SQL에서 부울을 출력하는 방법은 무엇입니까?

Question

나는 다른 테이블과 사전 필터 및 사전에 다른 테이블의 추상 열을 보았습니다. 컨텐츠가 신경 쓰지 않는 열이 하나 있지만 내용이 무효인지 아닌지 알아야합니다. 그래서 내 견해는 "진실"이 지정된 열의 값을 경우에 NULL이 아닙니다 그리고 "거짓"값의 경우 NULL입니다.

T-SQL로 이러한 부울을 선택하려면 어떻게해야합니까?

Answer 1

You have to use a CASE statement for this:

SELECT CASE WHEN columnName IS NULL THEN 'false' ELSE 'true' END FROM tableName;

Answer 2

Or you can do like this:

    SELECT RealColumn, CAST(0 AS bit) AS FakeBitColumn FROM tblTable

Answer 3

If you need a output as boolean

CAST(CASE WHEN colName IS NULL THEN 0  ELSE 1   END as BIT) aIsBooked

Answer 4

for the column in the view you can use something like

CASE WHEN ColumnName is not null THEN 'True' ELSE 'False' END

or in a statement

SELECT 
s.ID,
s.[Name],
CASE WHEN s.AchievedDate is not null THEN 'True' ELSE 'False' END [IsAchieved]
FROM Schools s

or for further processing afterwards I would personally use

SELECT 
s.ID,
s.[Name],
CASE WHEN s.AchievedDate is not null THEN 1 ELSE 0 END [IsAchieved]
FROM Schools s

Answer 5

I had a similar issue where I wanted a view to return a boolean column type based on if an actual column as null or not. I created a user defined function like so:

CREATE FUNCTION IsDatePopulated(@DateColumn as datetime)
RETURNS bit
AS
BEGIN
    DECLARE @ReturnBit bit;

    SELECT @ReturnBit = 
        CASE WHEN @DateColumn IS NULL 
            THEN 0 
            ELSE 1 
        END

    RETURN @ReturnBit
END

Then the view that I created returns a bit column, instead of an integer.

CREATE VIEW testView
AS
    SELECT dbo.IsDatePopulated(DateDeleted) as [IsDeleted] 
    FROM Company

Answer 6

You asked for boolean, which we call bit in t-sql.

Other answers have either given you a varchar 'true' and 'false' or 1 and 0. 'true' and 'false' are obviously varchar, not boolean. I believe 1 and 0 would be cast as an integer, but it's certainly not a bit. This may seem nit-picky, but types matter quite often.

To get an actual bit value, you need to cast your output explicitly as a bit like:

select case when tableName.columnName IS NULL then cast(0 as bit) else cast(1
as bit) END as ColumnLabel from tableName