WHERE + NOT EXIST + 2 Columns - sql

Question

I have a query, that should return all records in T1 that not linked to records in T2:
SELECT DISTINCT fldID, fldValue FROM T1
WHERE NOT EXISTS
(
SELECT T1.fldID, T1.fldValue
FROM T2
JOIN T1 ON T2.fldID = T1.fldPtr
)
But it returns empty set -- should be one record.
If I use query like this (clause on one field):
SELECT DISTINCT fldID FROM T1
WHERE fldID NOT IN
(
SELECT T1.fldID
FROM T2
JOIN T1 ON T2.fldID = T1.fldPtr
)
It returns correct result.
But the SQL Server do not support syntax
WHERE ( fldID, flrValue ) NOT IN ....
Help me please to figure out how to compose query that will check several columns?
Thanks!

Answer 1

You can also use EXCEPT for this:
SELECT DISTINCT fldID, fldValue FROM T1
EXCEPT
SELECT T1.fldID, T1.fldValue
FROM T2
JOIN T1 ON T2.fldID = T1.fldPtr

Answer 2

A more efficient and elegant query that will work with every database is:
SELECT T1.*
FROM T1
LEFT JOIN T2
ON T2.fldID = T1.fldPtr
AND T2.flrValue = T1.flrValue
WHERE T2.fldID IS NULL
The LEFT JOIN attempts to match using both criteria, then the WHERE clause filters the joins, and only non-joins have NULL values for the LEFT JOINed table.
This approach is IMHO pretty much the industry standard for finding non-matches. It is usually more efficient than a NOT EXIstS(), although several databases optimize a NOT EXISTS() to this query anyway.

Answer 3

Use both those columns if sub-query join:
SELECT DISTINCT fldID, fldValue FROM T1
WHERE NOT EXISTS
(
SELECT *
FROM T2
JOIN T1 ON T2.fldID = T1.fldPtr
AND T1.fldValue = T2.flrValue
)

Answer 4

Something like (I think, as I'm not sure I 100% understand your question):
SELECT DISTINCT fldID FROM T1
WHERE fldID NOT IN
(
SELECT T1.fldID
FROM T2
JOIN T1 ON T2.fldID = T1.fldPtr
WHERE T2.flrValue = T1.flrValue
)

Answer 5

If you have the same structure in both tables you can use the EXCEPT operator http://technet.microsoft.com/en-us/library/ms188055.aspx
In a more general case, you have to to use left join and find null elements in second table.

Answer 6

try the below Query.
select DISTINCT fldID
from Table1
WHERE cast(fldID as varchar(100))+'~'+cast(flrValue as varchar)
NOT IN (select cast(fldID as varchar(100))+'~'+cast(flrValue as varchar) from table2)

Answer 7

This is more easy query. It returns all T1.fldID that not linked to records in T2
SELECT DISTINCT T1.fldID
FROM T1
LEFT JOIN T2 ON T2.fldID = T1.fldPtr
WHERE T2.fldID IS NULL

Answer 8

Using IN to exclude a large number of values is terrible for performance. Try the following:
SELECT T1.*
FROM T1
LEFT JOIN T2 ON T2.fldID = T1.fldPtr AND T1.fldValue = T2.fldvalue
WHERE T2.fldID IS NULL

Answer 9

(from my comment:) you do not have to reference t1 again in the subquery. Doing so would cause a logic of the form select all the records from t1 that don't exist in t1 ..., which is always empty, just like select all blue balls that are not blue, or select all odd numbers that are even ...
The first query should be:
SELECT DISTINCT fldID, fldValue
FROM T1
WHERE NOT EXISTS (
SELECT * FROM T2
WHERE T2.fldID = T1.fldPtr
);
And: in your original query, the subquery is uncorrelated: The t1 in the subquery shadows the t1 in the main query, making the subquery not referring any table or alias from the main query: it returns either True (some row exists) or False, the result being totally uncorrelated to the rows in the main query. (yet another good reason to use aliases instead of real table names in your queries)