sql: check if entry in table A exists in table B

问题

I have a definition table that I know is not being maintained very well, lets call this table A. I have another table (call it table B) that is much smaller and ideally should be a subset of table A but I know that table A is somewhat stale and does not contain new entries that are in Table B.

Note, that tables A and B have different columns.

Table A:
ID, Name, blah, blah, blah, blah

Table B:
ID, Name

I want all rows in Table B such that the ID in Table B does NOT exist in Table A. This does not just match rows in Table A; I want only rows in Table B where the ID does NOT exist at all in Table A.

回答1:

SELECT *
FROM   B
WHERE  NOT EXISTS (SELECT 1 
                   FROM   A 
                   WHERE  A.ID = B.ID)

回答2:

The classical answer that works in almost every environment is

SELECT ID, Name, blah, blah
FROM TableB TB
LEFT JOIN TableA TA
ON TB.ID=TA.ID
WHERE TA.ID IS NULL

sometimes NOT EXISTS may be not implemented (not working).

回答3:

If you are set on using EXISTS you can use the below in SQL Server:

SELECT * FROM TableB as b
WHERE NOT EXISTS
(
   SELECT * FROM TableA as a
   WHERE b.id = a.id
)

回答4:

Or if "NOT EXISTS" are not implemented

SELECT *
FROM   B
WHERE (SELECT count(*)  FROM   A WHERE  A.ID = B.ID) < 1

来源：https://stackoverflow.com/questions/15938180/sql-check-if-entry-in-table-a-exists-in-table-b