http://dev.csdn.net/article/65/65909.shtm
SQL 里面最常用的命令是 SELECT 语句，用于检索数据。语法是：
SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
* | expression [ AS output_name ] [, ...]
[ INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table ]
[ FROM from_item [, ...] ]
[ WHERE condition ]
[ GROUP BY expression [, ...] ]
[ HAVING condition [, ...] ]
[ { UNION | INTERSECT | EXCEPT [ ALL ] } select ]
[ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
[ FOR UPDATE [ OF class_name [, ...] ] ]
[ LIMIT { count | ALL } [ { OFFSET | , } start ]]*******************************************************************as 是select部分列的别名，就是把别名作为列名显示；而from里面的别名是不需要用as关键字的，直接写就可以例如：SELECT S.SNAME, P.PNAME
FROM SUPPLIER S, PART P, SELLS SE
WHERE S.SNO = SE.SNO AND
P.PNO = SE.PNO;同时，看得出来，where子句里面是可以用缩写的。
