How to get efficiently values from a table that are not in another table?

Hi experts,

i have 2 database tables TAB1 and TAB2. Both tables have between 3 and 4 millions entries. The goal is to find out all entries in TAB1 that are not in TAB2.

The tables are some common key fields. An easy way to achieve this will be to loop on one internal table with data from TAB1 and then check if an entries is not in TAB2 and add it to a result list. Is there any way to resolve this efficiently. I am taking here about tables with million entries.

Thanks in advance.