sql – SELECT *语句中的列顺序 – 保证？

到目前为止,我的假设是返回的列是用于创建db表的DDL语句的顺序.到目前为止,这是有效的 – 但我想知道这只是运气,还是在(ANSI)SQL规范中专门解决.

即ANSI SQL(因此可能是数据库)是否保证SELECT *语句中返回的列的顺序？

我使用PostgreSQL 8.4作为我的后端数据库

>是的,我知道在ORM中使用手工制作的SQL语句会破坏ORM的目的,但需要……

解决方法

http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt

<query specification> ::=
          SELECT [ <set quantifier> ] <select list> <table expression>
[...]
<select list> ::=
            <asterisk>
          | <select sublist> [ { <comma> <select sublist> }... ]

[...]
Syntax Rules
1) Let T be the result of the <table expression>.
3) Case:
       a) [...]
       b) Otherwise,the <select list> "*" is equivalent to a <value
          expression> sequence in which each <value expression> is a
          <column reference> that references a column of T and each
          column of T is referenced exactly once. The columns are ref-
          erenced in the ascending sequence of their ordinal position
          within T.

所以,换句话说,是的,SQL标准指定根据它们在T中的序数位置来投射列.注意,当你的< table expression>时,事情变得有点棘手.由几个涉及JOIN … USING或NATURAL JOIN子句的表组成.但是,从简单的表中进行选择时,假设订单符合预期,您可能会很好.

为了完整起见,表格中T的序数位置的含义将在11.4< column definition>中进一步解释：

General Rules
     5) [...] The ordinal position included
        in the column descriptor is equal to the degree of T. [...]

然后在11.11< add column definition> (对于ALTER TABLE语句)

General Rules
     4) [...] In particular,the degree of T
        is increased by 1 and the ordinal position of that column is
        equal to the new degree of T as specified in the General Rules
        of Subclause 11.4,"<column definition>".

还有很多其他SQL语句和子句依赖于< table expressions>中的序数位置的正式规范.一些例子：

13.8 <insert statement> 
     (when omitting the `<insert column list>`)
20.2 <direct select statement: multiple rows>
     (when `<sort specification>` contains an `<unsigned integer>`)

特别是Postgres非常符合标准,所以如果你真的想要SELECT *,请继续！

（编辑：李大同）

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