Identifying which value in where clause is incorrect? - sql-server

Question

My SQL kung-fu is not strong. I want to know if I can identify which value of a WHERE clause is incorrect.
So say I execute the following SQL statement....
SELECT col1, col2, col3 FROM dbo.myTable WHERE col1 = 'ABC' and col2 = 123
I want to be able to identify either that the value 'ABC' for col1 doesn't exist OR that the value 123 for col2 does not exist.
This would be within a single query, as I want to avoid two queries if possible.
Where I execute the first, and if rows exist then I execute the second if no rows then I can derive that col2 is wrong.
SELECT col1, col2, col3 FROM dbo.myTable WHERE col1 = 'ABC'
SELECT col1, col2, col3 FROM dbo.myTable WHERE col1 = 'ABC' and col2 = 123
I have considered
SELECT 1 as qRow, col1, col2, col3 FROM dbo.myTable WHERE col1 = 'ABC'
UNION
SELECT 2 as qRow, col1, col2, col3 FROM dbo.myTable WHERE col1 = 'ABC' and col2 = 123
and based on the qRow value i can determine which value is missing within the table, but wanted to now if there was any other solution

Answer 1

If you want to find where col1 is not ABC or col2 is not 123, you can do this:
SELECT col1 ,
col2 ,
col3
FROM dbo.myTable
WHERE col1 <> 'ABC'
OR col2 <> 123

Answer 2

Are you looking for something like
SELECT col1, col2, col3,
CASE
WHEN col1 = 'ABC' and col2 = 123 THEN 'both_true'
WHEN col1='ABC' THEN 'col1_true'
ELSE 'col2_true'
END AS value_check
FROM dbo.myTable WHERE col1 = 'ABC' or col2 = 123

Answer 3

I think probably you can use NOT EXISTS like
SELECT col1, col2, col3
FROM dbo.myTable
WHERE NOT EXISTS ( select 1 from dbo.myTable
where col1 = 'ABC' or col2 = 123)

Answer 4

SELECT col1, col2, col3, case when col1 <> 'ABC' then 'X' end as 'MissingCol1Abc',
case when col2 <> 123 then 'X' end as MissingCol2
FROM dbo.myTable
WHERE col1 = 'ABC' OR col2 = 123
Or did you mean you want to know when the column is null?
SELECT col1, col2, col3, case when is null col1 then 'X' end as 'MissingCol1Abc',
case when col2 is null then 'X' end as MissingCol2
FROM dbo.myTable
WHERE col1 = 'ABC' OR col2 = 123

Answer 5

If you use an OR instead of AND you could add a CASE statement to show the matching column:
SELECT col1, col2, col3,
CASE WHEN col1 = 'ABC' THEN 'True' ELSE 'False' END as Col1Match,
CASE WHEN col2 = '123' THEN 'True' ELSE 'False' END as Col2Match
FROM dbo.myTable
WHERE col1 = 'ABC' OR col2 = 123
Sample SQL Fiddle
You will see in the sample fiddle, that rows are only returned where one or both items match.