SQL Joins.pdf
- 1. SQL Joins Source material from Code Project article by C.L. Moffatt and โCoding Horrorโ blog from 10/11/07
- 2. Types of Joins โข Inner Join โข Natural Join โข Left (Outer) Join โข Right (Outer) Join โข (Full) Outer Join โข Left (Outer) Join Excluding Inner Join โข Right (Outer) Join Excluding Inner Join โข (Full) Outer Join Excluding Inner Join โข Cross Join โข Equi-Join
- 3. Sample Tables PK Value 1 FOX 2 COP 3 TAXI 6 WASHINGTON 7 DELL 5 ARIZONA 4 LINCOLN 10 LUCENT TableA PK Value 1 TROT 2 CAR 3 CAB 6 MONUMENT 7 PC 8 MICROSOFT 9 APPLE 11 SCOTCH TableB
- 4. Inner Join โข Inner join produces only the set of records that match in both Table A and Table B โข Most commonly used, best understood join
- 5. Inner Join SELECT * FROM TableA INNER JOIN TableB ON TableA.PK = TableB.PK โข This is the same as doing SELECT * FROM TableA, TableB WHERE TableA.PK = TableB.PK TableA Value PK TableB PK Value FOX 1 1 TROT COP 2 2 CAR TAXI 3 3 CAB WASHINGTON 6 6 MONUMENT DELL 7 7 PC
- 6. Inner Join (continued) โข Inner Joins do not have to use equality to join the fields โข Can use <, >, <>
- 7. Inner Join (continued) SELECT * FROM TableA INNER JOIN TableB ON TableA.PK > TableB.PK TableA PK Value TableB PK Value 2 COP 1 TROT 3 TAXI 1 TROT 3 TAXI 2 CAR 4 LINCOLN 1 TROT 4 LINCOLN 2 CAR 4 LINCOLN 3 CAB 5 ARIZONA 1 TROT 5 ARIZONA 2 CAR 5 ARIZONA 3 CAB โฆ Moreโฆ Rowsโฆ
- 8. Inner Join/Natural Join โข A NATURAL join is just an inner equi-join where the join is implicitly created using any matching columns between the two tables โข Example: โข SELECT * FROM TableA NATURAL JOIN TableB โข Same results as inner equi-join? โข Which columns match?
- 9. Left Outer Join โข Left outer join produces a complete set of records from Table A, with the matching records (where available) in Table B. If there is no match, the right side will contain null.
- 10. Left Outer Join โข SELECT * FROM TableA LEFT OUTER JOIN TableB ON TableA.PK = TableB.PK TableA Value PK TableB PK Value FOX 1 1 TROT COP 2 2 CAR TAXI 3 3 CAB LINCOLN 4 NULL NULL ARIZONA 5 NULL NULL WASHINGTON 6 6 MONUMENT DELL 7 7 PC LUCENT 10 NULL NULL
- 11. Right Outer Join โข Right outer join produces a complete set of records from Table B, with the matching records (where available) in Table A. If there is no match, the left side will contain null.
- 12. Right Outer Join โข SELECT * FROM TableA RIGHT OUTER JOIN TableB ON TableA.PK = TableB.PK TableA Value PK TableB PK Value FOX 1 1 TROT COP 2 2 CAR TAXI 3 3 CAB WASHINGTON 6 6 MONUMENT DELL 7 7 PC NULL NULL 8 MICROSOFT NULL NULL 9 APPLE NULL NULL 11 SCOTCH
- 13. Full Outer Join โข Full outer join produces the set of all records in Table A and Table B, with matching records from both sides where available. If there is no match, the missing side will contain null.
- 14. Full Outer Join โข SELECT * FROM TableA FULL OUTER JOIN TableB ON TableA.PK = TableB.PK TableA Value PK TableB PK Value FOX 1 1 TROT COP 2 2 CAR TAXI 3 3 CAB LINCOLN 4 NULL NULL ARIZONA 5 NULL NULL WASHINGTON 6 6 MONUMENT DELL 7 7 PC LUCENT 10 NULL NULL NULL NULL 8 MICROSOFT NULL NULL 9 APPLE NULL NULL 11 SCOTCH
- 15. Full Outer Join in MySQL โข MySQL doesnโt have FULL OUTER JOIN โข Simulate using UNION, LEFT and RIGHT JOINs โข SELECT * FROM TableA LEFT JOIN TableB ON TableA.PK = TableB.PK UNION SELECT * FROM TableA RIGHT JOIN TableB ON TableA.PK = TableB.PK
- 16. Left Join Excluding Inner Join โข This query will return all of the records in the left table (table A) that do not match any records in the right table (table B).
- 17. Left Join Excluding Inner Join โข SELECT * FROM TableA LEFT JOIN TableB ON TableA.PK = TableB.PK WHERE TableB.PK IS NULL โข Perform left outer join, then exclude the records we don't want from the right side via a where clause. TableA Value PK TableB PK Value LINCOLN 4 NULL NULL ARIZONA 5 NULL NULL LUCENT 10 NULL NULL
- 18. Right Join Excluding Inner Join โข This query will return all of the records in the right table (table B) that do not match any records in the left table (table A).
- 19. Right Join Excluding Inner Join โข SELECT * FROM TableA RIGHT JOIN TableB ON TableA.PK = TableB.PK WHERE TableA.PK IS NULL โข Perform right outer join, then exclude the records we don't want from the left side via a where clause. TableA Value PK TableB PK Value NULL NULL 8 MICROSOFT NULL NULL 9 APPLE NULL NULL 11 SCOTCH
- 20. Full Outer Excluding Inner Join โข This query will return all of the records in Table A and Table B that do not have a matching record in the other table. โข (If you find a useful application, let me know! ๏)
- 21. Full Outer Excluding Inner Join โข SELECT * FROM TableA FULL OUTER JOIN TableB ON TableA.PK = TableB.PK WHERE TableA.PK IS NULL OR TableB.PK IS NULL TableA Value PK TableB PK Value NULL NULL 8 MICROSOFT NULL NULL 9 APPLE NULL NULL 11 SCOTCH LINCOLN 4 NULL NULL ARIZONA 5 NULL NULL LUCENT 10 NULL NULL
- 22. How Can We Do This in MySQL? โข MySQL doesnโt have FULL OUTER JOIN โข Simulate using UNION, LEFT and RIGHT JOINs โข SELECT * FROM TableA LEFT JOIN TableB ON TableA.PK = TableB.PK WHERE TableB.PK IS NULL UNION SELECT * FROM TableA RIGHT JOIN TableB ON TableA.PK = TableB.PK WHERE TABLEA.PK IS NULL
- 23. Cross Join โข A cross join is a Cartesian Product join โ it is every record in Table A combined with every record in Table B. โข It gives the same results as not using a WHERE clause when querying two tables in MySQL โข SELECT * from TableA CROSS JOIN TableB โข SELECT * from TableA, TableB