Question

I have two very large tables, Table1 and Table2. They look like this:

Table1 (800k records): Name, BirthDate, OrderNumber, col4, col5, col6.

Table2 (200k records): Name, BirthDate, OrderNumber, col4, col5, col6.

How can I select all records from table 1 which don’t have a matching Name, BirthDate, OrderNumber combination in table 2? The rest of the columns don’t matter.

I’ve tried doing this query below which runs for at least a couple minutes with no apparent end. Right now I am just trying to select the records then i can figure out how to combine the tables.

Select Table1.Name, Table1.BirthDate, Table1.OrderNumber from Table1
left join Table2 ON 
Table1.Name=Table2.Name AND
Table1.BirthDate=Table2.BirthDate AND
Table1.OrderNumber=Table2.OrderNumber AND 
WHERE Table2.Name IS NULL;

Answer 1

You can try this variation and see if it’s any better. You should also make sure you have Name, BirthDate and OrderNumber indexed.

SELECT t1.Name, t1.BirthDate, t1.OrderNumber
    FROM Table1 t1
    WHERE NOT EXISTS(SELECT NULL
                         FROM Table2 t2
                         WHERE t2.Name = t1.Name
                             AND t2.BirthDate = t1.BirthDate
                             AND t2.OrderNumber = t1.OrderNumber)