MySQL中 GROUP BY 子句语法及注意事项

基本语法

SELECT column_name,
       aggregate_function(column_name)  --聚集函数
FROM table
WHERE condition
GROUP BY column_name
HAVING condition
ORDER BY column_name;

SELECT column_name_1,
       column_name_2,
       aggregate_function(column_name)
FROM table
WHERE condition
GROUP BY column_name_1, column_name_2
HAVING condition
ORDER BY column_name;

主要功能

GROUP BY 子句，指示MySQL分组数据，然后对每个组而不是整个结果集进行聚集。

注意事项

除聚集计算语句外，SELECT语句中的每个列都必须在GROUP BY子句中给出。

GROUP BY子句必须出现在WHERE子句之后，ORDER BY子句之前。