查找零类别的单位

Question

我正在使用SQL命令查找没有类别的单元。以下是表格：

单元

id  name

UnitCategory

id  name

UnitCategoryIndex

id  categoryid  unitid

谢谢！

Answer 1

仔细检查语法（我为SQL Server编写）。

SELECT u.id, u.name
FROM Unit as u
LEFT JOIN UnitCategoryIndex as uci
ON u.id = uci.UnitId
where uci.id is null

Answer 2

SELECT id FROM Unit WHERE NOT EXISTS (SELECT 1 FROM UnitCategoryIndex WHERE Unit.id = UnitCategoryIndex.unitid)

Answer 3

select *
  from unit U
 where not exists ( select *
                      from unitcategoryindex X
                     where X.unitid = U.id
                  )