sql distinct关键字有什么用?
在表中,一个列可能会包含多个重复值,有时您也许希望仅仅列出不同(distinct)的值。
DISTINCT
关键词用于返回唯一不同的值。
在SELECT子句中,可以通过指明DISTINCT关键字,来去除数据列中的重复信息,返回唯一不同的值。
SQL SELECT DISTINCT 语法
SELECT DISTINCT column_name,column_name FROM table_name;
示例:
1、只对一个字段查重
对一个字段查重,表示选取该字段一列不重复的数据。
示例表: psur_list
PLAN_NUMBER字段去重,语句:
SELECT DISTINCT PLAN_NUMBER FROM psur_list;
结果如下:
2、多个字段去重
对多个字段去重,表示选取多个字段拼接的一条记录,不重复的所有记录
示例表: psur_list
PLAN_NUMBER和PRODUCT_NAME字段去重,语句:
SELECT DISTINCT PLAN_NUMBER,PRODUCT_NAME FROM psur_list;
结果如下:
期望结果:只对第一个参数PLAN_NUMBER取唯一值
解决办法一: 使用 group_concat 函数
语句:SELECT GROUP_CONCAT(DISTINCT PLAN_NUMBER) AS PLAN_NUMBER,PRODUCT_NAME FROM psur_list GROUP BY PLAN_NUMBER
解决办法二:使用group by
语句:SELECT PLAN_NUMBER,PRODUCT_NAME FROM psur_list GROUP BY PLAN_NUMBER
结果如下:
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