Question

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In MySQL queries, why use join instead of where?

Joins are always confusing for me..can anyone tell me what is difference between different joins and which one is quickest and when to use which join and what is difference between join and where clause ?? Plz give ur answer in detail as i already read about joins on some websites but didn’t get the concept properly.

Answer 1

Rather than quote an entire Wikipedia article, I’m going to suggest your their article on SQL Joins.

An SQL JOIN clause combines records
from two or more tables in a
database. It creates a set that
can be saved as a table or used as is.
A JOIN is a means for combining
fields from two tables by using values
common to each. ANSI standard SQL
specifies four types of JOINs: INNER,
OUTER, LEFT, and RIGHT. In special
cases, a table (base table, view, or
joined table) can JOIN to itself in a
self-join.

A programmer writes a JOIN predicate
to identify the records for joining.
If the evaluated predicate is true,
the combined record is then produced
in the expected format, a record set
or a temporary table, for example.

There is an older syntax that uses WHERE clauses to imply INNER JOINs. While it works, and will produce queries that run exactly like queries specified with the INNER JOIN syntax, it is deprecated because most people find it more confusing.

Here’s the documentation for the MySQL JOIN syntax.