I am trying to solve a problem. It seems that of a brain teaser if you ask me.
Given two tables, return only values from the first table when there is a match for EVERY record in a second table. So a record in table 1 must have a match to every record in table 2. If table 2 has fewer than every row I want to exclude it from the final result.
This must be done without using count, having, group by. I must solve it with union, intersect, except, exists.
I am using SQL Server BTW.
CREATE TABLE table1 (id int, lid int)
INSERT INTO table1 VALUES (1, 1),(1, 2),(1,3),(1,4),(2,1),(3,3),(4,4)
CREATE TABLE table2 (lid int)
INSERT INTO table2 VALUES (1),(2),(3),(4)
Table 1:
id lid
--------
1 1
1 2
1 3
1 4
2 1
3 3
4 4
Table2:
lid
-----
1
2
3
4
This method here is "not the way I am supposed to solve it". Frustrating because this solution is so simple and does exactly what it should do. I can't use count, group by, and having.
SELECT id
FROM dbo.table1, dbo.table2
WHERE table1.lid = table2.lid
GROUP BY id
HAVING COUNT(*) = (SELECT COUNT(*) FROM dbo.table2)
So basically I need to find a way to exclude the results from the first table when there is not a full set of matches in table 2. In this example the only value in table 1 with a match to every record in table 2 is 1. 2,3,4 would need to be excluded.
What you're looking for has a name. It's called relational division. It has no equivalent in SQL, although it can be emulated in a variety of ways. Joe Celko has written one of the most complete blog posts about the topic.
Since you must use some of the more basic relational operators in SQL, this could be one solution for you:
SELECT DISTINCT id
FROM table1 t1a
WHERE NOT EXISTS (
SELECT *
FROM table2
WHERE NOT EXISTS (
SELECT *
FROM table1 t1b
WHERE t1a.id = t1b.id
AND t2.lid = t1b.lid
)
)
It reads in English, informally:
Get me all the elements in
table1for which there is no element intable2, which doesn't match such an element fromtable1
Or also:
Get me the elements from
table1, which match all the elements intable2