Borrowing heavily from the writings of Microsoft, please consider TableA and TableB with ColumnA and ColumnB respectively. Here are the two outer joins in a WHERE clause:

TableA.ColumnA *= TableB.ColumnB

This means, "Show all values in ColumnA but only the values in ColumnB where they are equal to those in ColumnA."

TableA.ColumnA =* TableB.ColumnB

This means, "Show all values in ColumnB but only the values in ColumnA where they are equal to those in ColumnB."

An Outer Join cannot be used in the same SQL statement with an Equijoin. The prescence of Null values in columns used in an outer join produces unexpected results.