杭州交通信息网安徽大学校长信箱:SQL 语句的执行顺序 问题
来源：百度文库 编辑：杭州交通信息网 时间：2024/05/13 05:03:53
谢谢
好像不是吧 记得老师以前讲过的 有先后顺序 ，只是忘记了
sorry 我说的 是 select , from ,where ,order by,group 等关键字的执行顺序
SELECT
从数据库中检索行，并允许从一个或多个表中选择一个或多个行或列。虽然 SELECT 语句的完整语法较复杂，但是其主要的子句可归纳如下：
SELECT select_list
[ INTO new_table ]
FROM table_source
[ WHERE search_condition ]
[ GROUP BY group_by_expression ]
[ HAVING search_condition ]
[ ORDER BY order_expression [ ASC | DESC ] ]
可以在查询之间使用 UNION 运算符，以将查询的结果组合成单个结果集。
语法
SELECT statement ::=
< query_expression >
[ ORDER BY { order_by_expression | column_position [ ASC | DESC ] }
[ ,...n ] ]
[ COMPUTE
{ { AVG | COUNT | MAX | MIN | SUM } ( expression ) } [ ,...n ]
[ BY expression [ ,...n ] ]
]
[ FOR { BROWSE | XML { RAW | AUTO | EXPLICIT }
[ , XMLDATA ]
[ , ELEMENTS ]
[ , BINARY base64 ]
}
]
[ OPTION ( < query_hint > [ ,...n ]) ]
< query expression > ::=
{ < query specification > | ( < query expression > ) }
[ UNION [ ALL ] < query specification | ( < query expression > ) [...n ] ]
< query specification > ::=
SELECT [ ALL | DISTINCT ]
[ { TOP integer | TOP integer PERCENT } [ WITH TIES ] ]
< select_list >
[ INTO new_table ]
[ FROM { < table_source > } [ ,...n ] ]
[ WHERE < search_condition > ]
[ GROUP BY [ ALL ] group_by_expression [ ,...n ]
[ WITH { CUBE | ROLLUP } ]
]
[HAVING <search_condition>]
详细的请看一下sql的帮助文件。
一起执行,无分步执行
先括号后外面
先条件后排序