Work around for intersect keyword in mysql - mysql

Question

I have requirement of getting intersection of some results in mysql DB. But after googling came to know that there is no mysql intersect keyword available . Following are my sample tables.
gene table
+------+--------+---------+
| id | symbol | test_id |
+------+--------+---------+
| -1 | A | -1 |
| 8 | A | 3 |
| 9 | G | 3 |
| -1 | A | -1 |
| -2 | B | -1 |
| -3 | C | -1 |
| 1 | A | 1 |
| 2 | B | 1 |
| 3 | C | 1 |
| 4 | B | 2 |
| 5 | C | 2 |
| 6 | D | 2 |
| 7 | E | 2 |
| 8 | A | 3 |
| 9 | G | 3 |
| 10 | F | 3 |
| 11 | C | 3 |
| 12 | C | 4 |
| 13 | G | 4 |
| 14 | F | 4 |
| 15 | M | 4 |
| 16 | N | 4 |
+------+--------+---------+
test table
+------+-------+
| id | name |
+------+-------+
| -1 | test0 |
| 3 | test3 |
| -1 | test0 |
| 1 | test1 |
| 2 | test2 |
| 3 | test3 |
| 4 | test4 |
+------+-------+
Now I want to formulate a query which will give me the tests which are common for provided genes. e.g. I will provide gene A, B, C and I should get the following result:
id name id symbol
---------------------------
-1 | test0 | -1 | A
-1 | test0 | -2 | B
-1 | test0 | -3 | C
1 | test1 | 1 | A
1 | test1 | 2 | B
1 | test1 | 3 | C
I just tried to form a query by following way but didn't work, getting empty resultset and if I use 'or' in where clause getting tests for all genes in where clause.
select distinct t.id, t.name, g.id, g.symbol from tests t
join genes g on t.id = g.test_id
where g.symbol = 'A' and g.symbol='B' and g.symbol='C';
Please help me to construct the query.

Answer 1

The trick is to filter the records with your criteria, then group by test.id to check that it matches all the criteria:
SELECT t.id
FROM tests AS t
INNER JOIN genes AS g
ON t.id = g.test_id
WHERE g.symbol in ('A','B','C')
GROUP BY t.id
HAVING COUNT(DISTINCT g.symbol) = 3;
So the key line is here:
HAVING COUNT(DISTINCT g.symbol) = 3;
If, like test 2, there is only a match on 'B', then the count will return 1 and the test will be excluded. The number of items you are checking for must match the number in the HAVING clause.
If you then need to get the full data out, you just need to join back to your table:
SELECT t.id, t.name, g.id, g.symbol
FROM genes AS g
INNER JOIN
( SELECT t.id, t.name
FROM tests AS t
INNER JOIN genes AS g
ON t.id = g.test_id
WHERE g.symbol in ('A','B','C')
GROUP BY t.id, t.name
HAVING COUNT(DISTINCT g.symbol) = 3
) t
ON t.id = g.test_id;
Example on SQL Fiddle

Answer 2

Change those AND conditions to OR condition like below cause at any point in time g.symbol can hold only one value and not multiple value. that's why you are getting empty result set.
select t.id, t.name, g.id, g.symbol from tests t
join genes g on t.id = g.test_id
where (g.symbol = 'A' or g.symbol='B' or g.symbol='C')
and g.test_id = 1;
(OR) use a IN operator like
select t.id, t.name, g.id, g.symbol from tests t
join genes g on t.id = g.test_id
where g.symbol in ('A','B','C')
and g.test_id = 1;