子查询返回的值超过1。 当子查询遵循> =或将子查询用作表达式时，不允许这样做

Question

Subquery returned more than 1 value error. How to solve this?

SELECT top 1 address
FROM tblAdr A
WHERE A.pkey=
  (SELECT b.pkey FROM tblMachine b WHERE b.ADDRESS_PKEY IS NULL
  )

Answer 1

The subquery (the quantity in parentheses) is returning more than one pkey value, which isn't allowed because a single scalar value is required. If you are content with checking whether a pkey in tblAdr matches any of the values in the subquery, then you can use WHERE A.pkey IN (...) as follows:

SELECT TOP 1 address
FROM tblAdr A
WHERE A.pkey IN (SELECT b.pkey FROM tblMachine b WHERE b.ADDRESS_PKEY IS NULL)

Answer 2

Change the = to an IN

select top 1 address from tblAdr A where A.pkey in (select b.pkey from tblMachine b where b.ADDRESS_PKEY is null)

This should fix the error, however the logic of your query is likely flawed. You are after one row only ( select top 1 ), however you don't define what row should be chosen first (no order by clause).

Answer 3

Use IN instead of = as your subquery returns multiple matching rows.

SELECT top 1 address
FROM tblAdr A
WHERE A.pkey IN
  (SELECT b.pkey FROM tblMachine b WHERE b.ADDRESS_PKEY IS NULL
  );

Also, always use top queries with order by.

Answer 4

此子查询“从tblMachine b中选择b.pkey，其中b.ADDRESS_PKEY为null”返回多个值，您无法将其与“ =”运算符进行比较，但您需要此try in子句