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未总结—distinct、group by、update、desc、having 的用法，看看组合查询

https://www.codenong.com/141562/

group by

https://www.jianshu.com/p/8f35129dd2ab

update

要在原字段上做一个修改操作，可以使用concat函数用来字符串之间的连接

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DISTINCT

用于返回唯一不同的值
例如：SELECT DISTINCT column_name,column_name FROM table_name;

GROUP BY

根据一个或多个列对结果集进行分组
在分组的列上可以使用count、sum、avg等函数
例如
SELECT name, COUNT(*) FROM employee_tbl GROUP BY name;

UPDATE

UPDATE table_name SET field1=new-value1, field2=new-value2 [WHERE Clause]

having

having 字句可以筛选分组后的各组数据

SELECT column_name, aggregate_function(column_name)
FROM table_name
WHERE column_name operator value
GROUP BY column_name
HAVING aggregate_function(column_name) operator value;