来自一个表的SQL COUNT，其中来自另一个表的条件为真

Question

Okay, so let's say I have two tables, "TableA" and "TableB". In Table AI have a column "C", and in Table BI have a column "D" and a column "E".

TableA contains a lot of rows that can contain the same value in column C. TableB contains a lot of rows, but column D has to be unique (it's the autoincrement number). TableB's column E also can contain the same value in different rows. As well, column C and column D will contain the same numbers.

Example Tables

TableA

ID     C
----------
1      1
2      1
3      2

TableB

D    E
----------
1    1
2    0
3    0

Now, what I want to do is count all the rows in TableA in column C, which I have figured out how to do. However, I additionally want it to only give me as a result the count of C where the equivalent value in D also has an E of "1".

So, I have tried this, but it is failing and I cannot think of what I'm doing wrong or how to fix it. Googling for COUNT only gets me results dealing with one table.

In my example, I want it to COUNT C where the ID number that matches in TableB column D where E = 1 (so, where TableB column D = 1), and return that as the count, so I want it to return to me (or something to this effect):

c COUNT(*) Descending 1 2

SELECT TableA.C, COUNT(*) FROM TableA, TableB WHERE TableB.E = 1 GROUP BY TableA.C ORDER BY COUNT(*) DESC

If that makes any sense...

Answer 1

You don't join the two tables on the column

SELECT a.C, COUNT(*) FROM TableA a JOIN TableB b ON (C = D)
WHERE E GROUP BY a.C
ORDER BY COUNT(*) DESC