-- COL1,COL2,COL3SELECT
COL1,
CASE
WHEN COL2='A' THEN SELECT 名称 FROM A WHERE ID=C.COL3
WHEN COL2='B' THEN SELECT 名称 FROM B WHERE ID=C.COL3
END AS 名称
FROM C
COL1,
CASE
WHEN COL2='A' THEN SELECT 名称 FROM A WHERE ID=C.COL3
WHEN COL2='B' THEN SELECT 名称 FROM B WHERE ID=C.COL3
END AS 名称
FROM C
from C left join A on C.字段3 = A.ID
left join B on C.字段3 = B.ID
from C left join A on C.字段3 = A.ID
left join B on C.字段3 = B.ID
from C left join A on C.字段3 = A.ID AND C.字段2=‘A’
left join B on C.字段3 = B.ID AND C.字段2=‘B’
inner join不行吗?