Answer Posted / rekha d rathnam
1.Cross Join - is a join without a join contition
SELECT * FROM table-1 CROSS JOIN table-2
2.Inner Join - return only matched records
i.Equi-Join
ii.Non-Equi Join
* Inner joins or equi joins are the most common type of
joins, they use equality "=" of common attributes to join
tables.
SELECT projects.name AS "Project Name", teachers.name
FROM teachers, projects
WHERE teachers.id = projects.teacher;
* Like an inner join, but with an operator different
from "=" in the condition, e.g., not equal "<>".
SELECT projects.name AS "Project Name", teachers.name
FROM teachers, projects
WHERE teachers.id != projects.teacher;
3.Outer Join
i.Full Outer Join
11.Left Outer Join
iii.Right Outer Join
LEFT -- only unmatched rows from the left side table (table-
1) are retained
RIGHT -- only unmatched rows from the right side table
(table-2) are retained
FULL -- unmatched rows from both tables (table-1 and table-
2) are retained
SELECT assign.project, projects.name, assign.percentage
FROM projects LEFT OUTER JOIN assign
ON projects.id = assign.project ;
4.Self Join - With table aliases you can join a table to
itself.
SELECT DISTINCT *
FROM assign a, assign b
WHERE a.stud = 2 AND b.stud = 4 AND a.project = b.project;
5.Multi Join - The number of tables involved in a join are
not restricted.
SELECT DISTINCT assign.project, projects.name AS "Project",
assign.percentage, stud.name AS "Student"
FROM projects, assign, stud
WHERE projects.id = 1 AND projects.id = assign.project
AND assign.stud = stud.id ;
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