问题
I have the following table:
+-----------+--------+
| FirstName | Active |
+-----------+--------+
| Rob | TRUE |
| Jason | TRUE |
| Mike | FALSE |
+-----------+--------+
I would like to insert 'John' (with Active=True) only if an entry for John doesn't exist already where Active=True. I try the following:
insert into testTable (FirstName, Active) values ('John',True) where not exists (select 1 from testTable where FirstName='John' and Active=True)
but i get 'Query input must contain at least one table or query'.
Can anybody help with what I am trying to achieve?
回答1:
You can't combine Values with a WHERE clause. You need to use INSERT INTO ... SELECT instead.
Since you don't want to insert values from a table, you need to use a dummy table. I use MSysObjects for that purpose (that's a system table that always exists and always contains rows):
INSERT INTO testTable (FirstName, Active)
SELECT 'John', True
FROM (SELECT First(ID) From MSysObjects) dummy
WHERE NOT EXISTS (select 1 from testTable where FirstName='John' and Active=True)
回答2:
In my case the field already exist in the table so I changed it from an INSERT to an UPDATE query and it worked.
来源：https://stackoverflow.com/questions/52309940/ms-access-insert-where-not-exists