我有一张金属表
MetalID integer
MetalName text
MetalCode text
项目表
ItemID integer
ItemName text
...
Metal1 int Ref.-> metals.metalID
Metal2 int Ref.-> metals.metalID
Metal3 int Ref.-> metals.metalID
我正在尝试选择三个MetalCodes
SELECT m.MetalCode as 'Metal1', m.MetalCode as 'Metal2',m.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m ON m.metalID=k.metal1
INNER JOIN Metals AS m ON m.metalID=k.metal2
INNER JOIN Metals AS m ON m.metalID=k.metal3
WHERE k.ItemID=?
看起来我完全错了。请帮忙。
答案 0 :(得分:26)
您应该为表指定不同的别名。你打电话给他们所有人。
SELECT m1.MetalCode as 'Metal1', m2.MetalCode as 'Metal2',m3.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m1 ON m1.metalID=k.metal1
INNER JOIN Metals AS m2 ON m2.metalID=k.metal2
INNER JOIN Metals AS m3 ON m3.metalID=k.metal3
WHERE k.ItemID=?
答案 1 :(得分:8)
嗯,不是完全错误。 ;)
无论您拥有“INNER JOIN Metals AS m ”,m
都必须是独一无二的(每次都不是m
)。
尝试这样的事情(未经测试):
SELECT m1.MetalCode as 'Metal1', m2.MetalCode as 'Metal2', m3.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m1 ON m1.metalID=k.metal1
INNER JOIN Metals AS m2 ON m2.metalID=k.metal2
INNER JOIN Metals AS m3 ON m3.metalID=k.metal3
WHERE k.ItemID=?
答案 2 :(得分:2)
试试这个:
SELECT m.MetalCode as 'Metal1', n.MetalCode as 'Metal2'o.MetalCode as 'Metal3'
FROM Item as k INNER JOIN Metals AS m ON m.metalID=k.metal1
INNER JOIN Metals AS n ON n.metalID=k.metal2
INNER JOIN Metals AS o ON o.metalID=k.metal3
WHERE k.ItemID=?
答案 3 :(得分:1)
SELECT m1.MetalCode as 'Metal1', m2.MetalCode as 'Metal2',m3.MetalCode as 'Metal3'
FROM Item as k
INNER JOIN Metals AS m1 ON m1.metalID=k.metal1
INNER JOIN Metals AS m2 ON m2.metalID=k.metal2
INNER JOIN Metals AS m3 ON m3.metalID=k.metal3
WHERE k.ItemID=?
或更简单但每行获得一个金属码
SELECT MetalCode
FROM Item
WHERE metalID = metal1 OR metalID = metal2 OR metalID = metal3