Deleting from an aliased join construct - tsql

Question

I want to delete from a join construct, that I have to supply an alias ("mapped") for, since I also have to use an EXISTS clause on the join in the end. So the whole thing looks something like that:
DELETE a
FROM (TableA a INNER JOIN
(SELECT * FROM TableX x INNER JOIN TableY y ON x.id = y.id) map
ON a.key = map.key) mapped
WHERE EXISTS
(SELECT *
FROM LookUp l
WHERE l.key1 = mapped.TableAKey
AND l.key2 = mapped.TableXKey
AND l.key3 = mapped.TableYKey)
The problem seems to be with the parenthesis, because I get an error:
Incorrect syntax near 'mapped'.
Any help would be appreciated.

Answer 1

Just rewrite it so you're deleting from an explicit table and handle all of your conditions in the where clause something like this.
DELETE TableA
WHERE
EXISTS (
SELECT *
FROM
TableX x
INNER JOIN TableY y ON x.id = y.id
WHERE
x.key = TableA.key and
EXISTS (
SELECT *
FROM LookUp l
WHERE l.key1 = TableA.TableAKey
AND l.key2 = x.TableXKey
AND l.key3 = y.TableYKey
)
)
Also note it may be helpful to replace DELETE TableA with SELECT * FROM TableA while you're working on the where clause to see exactly what records are going to be deleted.

Answer 2

I believe the DELETE statement needs to reference an alias used in your FROM clause. Since your alias is 'mapped', try changing the DELETE as follows:
DELETE mapped
FROM (TableA a INNER JOIN
(SELECT * FROM TableX x INNER JOIN TableY y ON x.id = y.id) map
ON a.key = map.key) mapped
WHERE EXISTS
(SELECT *
FROM LookUp l
WHERE l.key1 = mapped.TableAKey
AND l.key2 = mapped.TableXKey
AND l.key3 = mapped.TableYKey)