具體操作
MySQL支持Select和某些Update和Delete情況下的Join語法,具體語法上的細節有:
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)
除了常用的兩個表連接之外,SQL(MySQL) JOIN 語法還支持多表連接。多表連接基本語法如下:
... FROM table1 INNER|LEFT|RIGHT JOIN table2 ON condition INNER|LEFT|RIGHT JOIN table3 ON condition ...
JOIN 多表連接實現了從多個表中獲取相關數據,下面是三個原始數據表:
article 文章表: aid title content uid tid 1 文章1 文章1正文內容... 1 1 2 文章2 文章2正文內容... 1 2 3 文章3 文章3正文內容... 2 1 5 文章5 文章5正文內容... 4 1 user 用戶表: uid username email 1 admin admin@5idev.com 2 小明 xiao@163.com 3 Jack jack@gmail.com type 文章類型表: tid typename 1 普通文章 2 精華文章 3 草稿
代碼如下 復制代碼SELECT * FROM t1 LEFT JOIN (t2, t3, t4) ON (t2.a=t1.a AND t3.b=t1.b AND t4.c=t1.c)