SQL Join is used to fetch data from two or more tables, which is joined to appear as single set of data. SQL Join is used for combining column from two or more tables by using values common to both tables.
Join Keyword is used in SQL queries for joining two or more tables.Types of Join
- Inner
- Outer
- Left
- Right
Student
| Reg_id | name | address | sub_id |
|---|---|---|---|
| 2008/SP/67 | Thenuzan | Kurumankadu | CSC |
| 2008/SP/20 | Nilashan | Poonthodam | CSC |
| 2008/SP/41 | Tharopan | Chunaakam | PHY |
| 2008/SP/34 | Pancha | Vadukkoodai | PHY |
Subject
| sub_id | sub_name |
|---|---|
| CSC | Computer Science |
| PHY | Physics |
| CHE | Chemistry |
CROSS JOIN /Cartesian Product
This type of JOIN returns the cartesian product of rows of from the tables in Join. It will return a table which consists of records which combines each row from the first table with each row of the second table.
SELECT column-name-list from tableA CROSS JOIN tableB;
SELECT * from Student CROSS JOIN Subject
| Reg_id | name | address | sub_id | sub_id | sub_name |
|---|---|---|---|---|---|
| 2008/SP/67 | Thenuzan | Kurumankadu | CSC | CSC | Computer Science |
| 2008/SP/67 | Thenuzan | Kurumankadu | CSC | PHY | Physics |
| 2008/SP/67 | Thenuzan | Kurumankadu | CSC | CHE | Chemistry |
| 2008/SP/20 | Nilashan | Poonthodam | CSC | CSC | Computer Science |
| 2008/SP/20 | Nilashan | Poonthodam | CSC | PHY | Physics |
| 2008/SP/20 | Nilashan | Poonthodam | CSC | CHE | Chemistry |
INNER JOIN
The INNER JOIN selects all rows from both participating tables as long as there is a match between the columns. An SQL INNER JOIN is same as JOIN clause, combining rows from two or more tables.
SELECT * FROM tableA INNER JOIN tableB ON tableA.column_name = tableB.column_name;
