While there are other types of JOINs supported by various flavors of SQL, most implementations of SQL support the INNER JOIN, LEFT JOIN, and RIGHT JOIN constructs.

I'm writing some code in C# where I need to (inner?) join two tables into a DataSet / DataTable.Essentially, I have two tables. Both have columns called "TestId" and "OperationId". Both are ...

In this SQL Server tip, Arthur Fuller explains the effects of NULLs, and the different results obtained by inner and outer JOINs.