Looking-up data with LEFT OUTER JOIN

In the previous topic we had shown the INNER JOIN. Removing the data from the left table was not desired in the example. This is different with the LEFT OUTER JOIN . Here the left table always remains complete. Only the data records that find a JOIN partner are read from the right-hand table.

Combinatorics for LEFT OUTER JOIN

  • All records from the left table are included in the found set.
  • Data records from the right-hand tables are only included in the result set if they find at least one partner in the left-hand table. In the example: EUR, ALL and USD
  • Data records in the right-hand table without a partner do not appear in the result. In the example: GBP from the right table.
  • If a record from the left table finds more than one partner, then it is multiplied accordingly. This is often not desirable.