select count(distinct(nameAndAge)) from ( select concat(name,age) as nameAndAge FROM student_info ) newtable // 别名表很重要 select distinct(nameAndAge),id,name,age from ( select concat(name,age) as nameAndAge FROM student_info ) newtable // 别名表很重要 //多个字段去重并显示多个字段 指定age排序 select distinct(nameAndAge),id,name,age from ( select id,name,age, concat(name,age) as nameAndAge FROM student_info GROUP BY age desc ) newtable GROUP BY nameAndAge //单个字段 select distinct(name) FROM student_info //显示多个字段 必须加where条件 select distinct(name),id,age FROM where age=14 student_info GROUP BY name //distinct 多字段处理效率慢,可以通过 group by功能去重 //单个age去重 select id,name,age FROM student_info GROUP BY age desc //多个字段(不严谨) select id,name,age FROM student_info GROUP BY name,age desc //严谨 select id,name,age,concat(name,age) as nameAndAge FROM student_info GROUP BY nameAndAge desc //排序,先去重 再排序 select * from( select id,name,age,concat(name,age) as nameAndAge FROM student_info GROUP BY nameAndAge desc )newtab where 1=1 ... GROUP BY age desc
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