What are joins..how many types of joins are there?

Answer Posted / john

Depending on condition existence
----CROSS JOIN (synonyms also CARTESIAN JOIN, CARTESIAN PRODUCT)
----NATURAL JOIN
----# NAMED COLUMNS JOIN - syntactic notation joining source
tables on user defined columns having the same name. This is
less dangerous than Natural join and just short form of
writing Equi joins on some common columns joined together.
Named columns joins always are Equi joins.
----# CONDITIONAL JOIN - fully controllable syntax by user.
This is the most widespread and most useful syntactic
convention. Depending on used predicates in join condition
it may be Equi join as well as Non-equi join.

Depending on row selection
INNER JOIN
OUTER JOIN--- left,right,full

Depending on comparison operator
equi Non-equi

Depending on used tables
SELF JOIN

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