How to write a T-Sql query that would output 1 if the value in a column in Table A matches the value in a column in Table B, 0 otherwise?

Question

I am using SQL Server 2012 and I need to write a query that would do give me the following output:

Code       Value
FRBAR        0
ENSPA        1
DEWINE       1
     ...

To achieve the above, I am working with 2 specific tables in my database, namely Table A and Table B. Table A has a column called CodeA and Table B has a column called CodeB .

I want to write a T-sql query that would match all the values in column CodeA with those in column CodeB and ouput the result I mentioned above.

I know I need to do a JOIN on these 2 columns but I am confused about how to implement the logic of returning a 1 if there is a match and a 0 otherwise.

Answer 1

You need to use a FULL OUTER JOIN :

SELECT CASE 
          WHEN CodeA IS NOT NULL THEN CodeA
          ELSE CodeB
       END AS Code,
       CASE 
          WHEN CodeA IS NOT NULL AND CodeB IS NOT NULL THEN 0
          ELSE 1
       END AS Value
FROM TableA
FULL OUTER JOIN TableB ON CodeA = CodeB

If there is a match the query will output 1 as Value . Otherwise the query will output 0 along with the not null code value.

Note: Using a LEFT JOIN will check only in one direction , ie only for codes in one table that don't exist in the other table. If you want to check in both directions , then you have to use a FULL JOIN .

Answer 2

You should use LEFT OUTER JOIN to take all records from TableA even then there is no matching records from TableB and then use case-when-else structure relying on absence(checking is NULL ) of TableB part of resulting record.

select TableA.CodeA Code, 
case when
TableB.CodeB is null then 0
else 1
end Value
from TableA left outer join TableB on TableA.CodeA = TableB.CodeB

Answer 3

Use LEFT JOIN . This will match the two tables on Code column and return NULL if there is no match. You can then use CASE to return 0 or 1 accordingly.

Answer 4

I would use CASE and LEFT JOIN

SELECT A.codeA code, 
       CASE WHEN B.codeB IS NULL THEN 0 ELSE 1 END
FROM A
LEFT JOIN B ON A.codeA = B.codeB