PSQL supports two-table outer joins as specified in the Microsoft ODBC documentation. In addition to simple two-table outer joins, PSQL supports
n-way nested outer joins.
The search condition (SearchCond) contains join conditions which in their usual form are LT.ColumnName = RT.ColumnName, where
LT is left table,
RT is right table, and
ColumnName represents some column within a given domain. Each predicate in the search condition must contain some nonliteral expression.
Notice the NULL entry for Franky Avalon in the table. That is because no DeptID of D103 was found in the Dept table. In a standard (INNER) join, Franky Avalon would have been dropped from the result set altogether.
If there is no right table row where the ON condition is TRUE, (it is FALSE for all right table rows given the current left table row), create a row instance of the right table with all column values NULL.
This query returns the same results as shown in Table 34, assuming there are no NULL values for EmpID in Emp and EmpID is a unique valued column. This query, however, is not optimized as well as the one show for Table
34 and can be much slower.