SQL NOT IN Clause

偶尔善良 提交于 2019-12-22 09:50:16

问题


I have a query which is not working as expected

Q1:
SELECT id, name 
FROM vw_x 
WHERE id NOT IN (select pid from table_x)
GROUP BY id, name
Having max(c_date) > GETDATE()

Q2:
SELECT id, name 
FROM vw_x 
GROUP BY id, name
Having max(c_date) > GETDATE()

Q1 is not returning anything even though i know those ids are not in table_x Q2 runs correctly without NOT IN

What could be wrong with my query?


回答1:


you have a NULL value in the table

try this

SELECT id, name 
FROM vw_x 
WHERE id NOT IN (select pid from table_x where pid is not null)
GROUP BY id, name
Having max(c_date) > GETDATE()

or this

SELECT id, name 
FROM vw_x 
WHERE  NOT EXISTS (select 1 from table_x  where pid = vw_x.id  )
GROUP BY id, name
Having max(c_date) > GETDATE()

See also Select all rows from one table that don't exist in another table




回答2:


what about using a left join?

SELECT id, name 
FROM vw_x 
LEFT JOIN table_x on id = pid
WHERE pid IS NULL
GROUP BY id, name
Having max(c_date) > GETDATE()



回答3:


There is another situation: the subquery may return nothing. SQL Server does not work as expected if the NOT IN clause returns a null list. I have a query like the following:

select * from table where id not in (select id from tableB where somecondition(x))

When the subquery contains a list of ids, the query will return the data as expected. But when the subquery returns nothing, the query will still return data, but then becomes stuck.

I changed the query to the following and solved the problem:

select * from table where id not in (select id from tableB where somecondition(x) **union all select 0**)

which makes sure the subquery will contain at least one number.



来源:https://stackoverflow.com/questions/2187780/sql-not-in-clause

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