What's the difference between LEFT, RIGHT, INNER, OUTER, JOIN?


The difference is in the way tables are joined if there are no common records.

JOIN is same as INNER JOIN and means to only show records common to both tables. Whether the records are common is determined by the fields in join clause. For example:

FROM t1
JOIN t2 on t1.ID = t2.ID

means show only records where the same ID value exists in both tables.

LEFT JOIN is same as LEFT OUTER JOIN and means to show all records from left table (i.e. the one that precedes in SQL statement) regardless of the existance of matching records in the right table.

RIGHT JOIN is same as RIGHT OUTER JOIN and means opposite of LEFT JOIN, i.e. shows all records from the second (right) table and only matching records from first (left) table.


Do you find this FAQ incorrect or incomplete? Please e-mail us what needs to be changed. To ensure quality, each change is checked by our editors (and often tested on live Firebird databases), before it enters the main FAQ database. If you desire so, the changes will be credited to your name. To learn more, visit our add content page.

If you are a commercial tool maker and your tool features a great way to handle the issue written about in this FAQ, please check out our advertisement page.



All contents are copyright © 2007-2014 FirebirdFAQ.org unless otherwise stated in the text.


Links   Firebird   News   FlameRobin   Home Inventory powered by FB  
Add content   Advertise   About  

Categories
 Newbies
 SQL
 Installation and setup
 Backup and restore
 Performance
 Security
 Connectivity and API
 HOWTOs
 Errors and error codes
 Miscellaneous