DQL: Database Query Language
1、查询某字段去重复
- select distinct xxxx from xxxx
2、合并字段查询函数concat( )、concat_ws( )
- select concat(user_name, password) from user;
- select concat(user_name, password) as user_name_email from user;
- select concat_ws(‘->’, user_name, password) from user; // 查询结果用’->’分隔符隔开
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