SQL Select 完整语法、主要子句、优先级

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>]

优先级：

GROUP BY --> HAVING --> ORDER BY --> TOP 10 *