A Cartesian product is returned when join conditions are not specified in a PROC SQL join. In a Cartesian product, each row from the first table is combined with every row from the second table.

This PROC SQL query is an inner join. It combines the rows from the first table that match rows from the second table, based on the matching criteria that are specified in the WHERE clause. Columns are not overlaid, so all columns from the referenced tables (including any columns with duplicate names) are displayed. Any unmatched rows from either table are not displayed.

This PROC SQL query is a left outer join, which retrieves all rows that match across tables (based on the join conditions in the ON clause), plus nonmatching rows from the left (first) table. No columns are overlaid, so all columns from both tables are displayed.

Inner joins combine the rows from the first table that match rows from the second table, based on one or more join conditions in the WHERE clause. The columns being matched must have the same data type, but they are not required to have the same name. For joins, the tables being joined can have different numbers of columns, and the rows do not need to be sorted.

In order to generate the same output as the DATA step and PROC PRINT steps, the PROC SQL full outer join must use the COALESCE function with the duplicate columns specified as arguments.

The use of summary functions does not require the use of table aliases. All of the other statements about table aliases that are shown here are true.

If you are joining two tables that contain a same-named column, you must use a prefix to specify the table or tables from which you want the column to be read. Remember that if you join tables that do not contain columns that have matching data values, you can produce a huge amount of output. Be sure to specify a WHERE clause to select only the rows that you want.