How do I compare two columns for equality in SQL Server? - sql

Question

I have two columns that are joined together on certain criteria, but I would also like to check if two other columns are identical and then return a bit field if they are.
Is there a simpler solution than using CASE WHEN?
Ideally I could just use:
SELECT Column1 = Column2 AS MyDesiredResult
FROM Table1
INNER JOIN Table2 ON Table1.PrimaryKey = Table2.ForeignKey

Answer 1

What's wrong with CASE for this? In order to see the result, you'll need at least a byte, and that's what you get with a single character.
CASE WHEN COLUMN1 = COLUMN2 THEN '1' ELSE '0' END AS MyDesiredResult
should work fine, and for all intents and purposes accomplishes the same thing as using a bit field.

Answer 2

CASE WHEN is the better option
SELECT
CASE WHEN COLUMN1 = COLUMN2
THEN '1'
ELSE '0'
END
AS MyDesiredResult
FROM Table1
INNER JOIN Table2 ON Table1.PrimaryKey = Table2.ForeignKey

Answer 3

The use of IIF? And it depends on version of SQL Server.
SELECT
IIF(Column1 = Column2, 1, 0) AS MyDesiredResult
FROM Table;

Answer 4

I'd go with the CASE WHEN also.
Depending on what you actually want to do, there may be other options though, like using an outer join or whatever, but that doesn't seem to be what you need in this case.

Answer 5

Regarding David Elizondo's answer, this can give false positives. It also does not give zeroes where the values don't match.
Code
DECLARE #t1 TABLE (
ColID int IDENTITY,
Col2 int
)
DECLARE #t2 TABLE (
ColID int IDENTITY,
Col2 int
)
INSERT INTO #t1 (Col2) VALUES (123)
INSERT INTO #t1 (Col2) VALUES (234)
INSERT INTO #t1 (Col2) VALUES (456)
INSERT INTO #t1 (Col2) VALUES (1)
INSERT INTO #t2 (Col2) VALUES (123)
INSERT INTO #t2 (Col2) VALUES (345)
INSERT INTO #t2 (Col2) VALUES (456)
INSERT INTO #t2 (Col2) VALUES (2)
SELECT
t1.Col2 AS t1Col2,
t2.Col2 AS t2Col2,
ISNULL(NULLIF(t1.Col2, t2.Col2), 1) AS MyDesiredResult
FROM #t1 AS t1
JOIN #t2 AS t2 ON t1.ColID = t2.ColID
Results
t1Col2 t2Col2 MyDesiredResult
----------- ----------- ---------------
123 123 1
234 345 234 <- Not a zero
456 456 1
1 2 1 <- Not a match

Answer 6

A solution avoiding CASE WHEN is to use COALESCE.
SELECT
t1.Col2 AS t1Col2,
t2.Col2 AS t2Col2,
COALESCE(NULLIF(t1.Col2, t2.Col2),NULLIF(t2.Col2, t1.Col2)) as NULL_IF_SAME
FROM #t1 AS t1
JOIN #t2 AS t2 ON t1.ColID = t2.ColID
NULL_IF_SAME column will give NULL for all rows where t1.col2 = t2.col2 (including NULL).
Though this is not more readable than CASE WHEN expression, it is ANSI SQL.
Just for the sake of fun, if one wants to have boolean bit values of 0 and 1 (though it is not very readable, hence not recommended), one can use (which works for all datatypes):
1/ISNULL(LEN(COALESCE(NULLIF(t1.Col2, t2.Col2),NULLIF(t2.Col2, t1.Col2)))+2,1) as BOOL_BIT_SAME.
Now if you have one of the numeric data types and want bits, in the above LEN function converts to string first which may be problematic,so instead this should work:
1/(CAST(ISNULL(ABS(COALESCE(NULLIF(t1.Col2, t2.Col2),NULLIF(t2.Col2, t1.Col2)))+1,0)as bit)+1) as FAST_BOOL_BIT_SAME_NUMERIC
Above will work for Integers without CAST.
NOTE: also in SQLServer 2012, we have IIF function.

Answer 7

The closest approach I can think of is NULLIF:
SELECT
ISNULL(NULLIF(O.ShipName, C.CompanyName), 1),
O.ShipName,
C.CompanyName,
O.OrderId
FROM [Northwind].[dbo].[Orders] O
INNER JOIN [Northwind].[dbo].[Customers] C
ON C.CustomerId = O.CustomerId
GO
NULLIF returns the first expression if the two expressions are not equal. If the expressions are equal, NULLIF returns a null value of the type of the first expression.
So, above query will return 1 for records in which that columns are equal, the first expression otherwise.