[SQL基础教程] 2-1 SELECT语句基础

[SQL基础教程] 2-1 SELECT语句基础

列的查询

SELECT<列名>,.....
FROM<表名>;

SELECT col_1, col_2
FROM table;

查询所有列

SELECT *
FROM <表名>;

SELECT *
FROM table;

为列设定别名

SELECT col_1 AS col1,
col_2 AS col2
col_2 AS "汉语别名"
FROM table;

常数的查询

SELECT '商品' AS col_4,'2009-02-14' AS col_5, 12 AS col_6
FROM table;

从结果中删除重复行

// 单列
SELCET DISTINCT col_1
FROM table;

// 多列
/*DISTINCT关键字仅添加在第一列上*/
SELCET DISTINCT col_1,col_2
FROM table;

WHERE

SELECT <列名>,.....
FROM <表名>
WHERE<条件表达式>;

注释