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JOIN

Is used to combine rows from two or more tables, based on a related column between them

(INNER) JOIN : Returns records that have matching values in both tables

LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table

RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the table left table

FULL (OUTER) JOIN : Returns all records when there is a match in either left or right table

INNER JOIN

Selects records that have matching values in both tables

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

LEFT JOIN

Returns all records from the left table (table1), and the matching records from the right table(table2)

The result is 0 records from the right side, if there is no match

In some databases LEFT JOIN is called LEFT OUTER JOIN

SELECT colum_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
-- vice versa

FULL JOIN

Returns all matching records from both tables whether the other table matches or not

Can potentially return very large result-sets

SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table.column_name = table2.column_name
WHERE condition;
-- FULL OUTER JOIN and FULL JOIN are the same

Self JOIN

Is a regular join, but the table is joined with itself

SELECT column_name(s)
FROM table1 T1, table1 T2
WHERE condition;