How to Check to See if a Record Exists in Oracle. Though SQL (Structured Query Language) for databases has proved to be indispensable through decades of use, differences among SQL versions can ...

By understanding the difference between IN, EXISTS, NOT IN, and NOT EXISTS, you can avoid a very common problem when NULLs appear in the data of a subquery. Scott Stephens helps you understand ...

Null means "undefined" in SQL, so numerous online services don't think Christopher Null exists.