在 SQL DB2 中，如何检查一个表中的值列表是否在另一个表中可用？

Question

I have two tables. One is a comparatively small table with 20000 records with columns with id(Unique key),name, zipcode. And the other is a huge table with nearly 1 billion+ records with columns id(unique key), name, age, address & active status(boolean). I want to have the records which are not active in the second table and check if those inactive records are available in the first table. I don't know how to loop the records in the first table as a single query. How can I do that in Db2?

Answer 1

You may use EXISTS logic here:

SELECT t1.*
FROM Table1 t1
WHERE EXISTS (SELECT 1 FROM Table2 t2 WHERE t2.id = t1.id AND t2.status = false);

Note that the above query might benefit from the following index on the second table:

CREATE INDEX idx2 ON Table2 (id, status);

This might let the lookup proceed much faster. Note that we chose to express your logic by scanning the first table, and looking up in the second, as the first table is much smaller than the second.