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具体操作
MySQL支持Select和某些Update和Delete情况下的Join语法，具体语法上的细节有：
table_references:
table_reference [, table_reference] …
table_reference:
table_factor
| join_table
table_factor:
tbl_name [[AS] alias]
[{USE|IGNORE|FORCE} INDEX (key_list)]
| ( table_references )
| { OJ table_reference LEFT OUTER JOIN table_reference
ON conditional_expr }
join_table:
table_reference [INNER | CROSS] JOIN table_factor [join_condition]
| table_reference STRAIGHT_JOIN table_factor
| table_reference STRAIGHT_JOIN table_factor ON condition
| table_reference LEFT [OUTER] JOIN table_reference join_condition
| table_reference NATURAL [LEFT [OUTER]] JOIN table_factor
| table_reference RIGHT [OUTER] JOIN table_reference join_condition
| table_reference NATURAL [RIGHT [OUTER]] JOIN table_factor
join_condition:
ON conditional_expr | USING (column_list)
除了常用的两个表连接之外，SQL（MySQL） JOIN 语法还支持多表连接。多表连接基本语法如下：
... FROM table1 INNER|LEFT|RIGHT JOIN table2 ON condition INNER|LEFT|RIGHT JOIN table3 ON condition ...
JOIN 多表连接实现了从多个表中获取相关数据，下面是三个原始数据表：
SELECT * FROM t1 LEFT JOIN (t2, t3, t4) ON (t2.a=t1.a AND t3.b=t1.b AND t4.c=t1.c)