SQLite GROUP BY子句

SQLite GROUP BY子句与SELECT语句一起使用，将相同的相同元素合并成一个组。

GROUP BY子句与SELECT语句中的WHERE子句一起使用，并且WHERE子句在ORDER BY子句之前。

语法：

SELECT column-list  
FROM table_name  
WHERE [ conditions ]  
GROUP BY column1, column2....columnN  
ORDER BY column1, column2....columnN

下面举个例子来说明如何使用GROUP BY子句。 假设有一个名为student的表，具有以下数据：

sqlite> select * from student;
1|Maxsu|27|Shengzhen|20000.0
2|Minsu|25|Beijing|15000.0
3|Avgsu|23|Shanghai|2000.0
4|Linsu|25|Guangzhou|65000.0
5|Sqlsu|26|Haikou|25000.0
6|Javasu|21|Shengzhen|18000.0
sqlite>

使用GROUP BY查询每位学生的费用总额：

SELECT NAME, SUM(FEES) FROM STUDENT GROUP BY NAME;

执行上面代码，得到以下结果 -

现在，使用以下INSERT语句向student表中创建一些记录，为了更好演示，插入的部分列的数据值是相同的：

INSERT INTO STUDENT VALUES (7, 'Linsu', 27, 'Haikou', 10000.00 );  
INSERT INTO STUDENT VALUES (8, 'Minsu', 23, 'Guangzhou', 5000.00 );  
INSERT INTO STUDENT VALUES (9, 'Maxsu', 23, 'Shenzhen', 9000.00 );

执行上面语句插入数据后，现在表中存在的数据如下 -

sqlite> select * from student;
1|Maxsu|27|Shengzhen|20000.0
2|Minsu|25|Beijing|15000.0
3|Avgsu|23|Shanghai|2000.0
4|Linsu|25|Guangzhou|65000.0
5|Sqlsu|26|Haikou|25000.0
6|Javasu|21|Shengzhen|18000.0
7|Linsu|27|Haikou|10000.0
8|Minsu|23|Guangzhou|5000.0
9|Maxsu|23|Shenzhen|9000.0
sqlite>

如上所示，现在有几个字段：name,age和city中的值是相同的。

现在，使用GROUP BY语句按NAME列来分组并对同分组内的所有的记录的fees列求和：

 select name, sum(fees) from student group by name;

执行上面代码，得到以下结果 -

可以使用ORDER BY子句和GROUP BY按升序或降序排列数据。

SELECT NAME, SUM(FEES) AS total_fees FROM STUDENT GROUP BY NAME ORDER BY NAME DESC;
-- 或者
SELECT NAME, SUM(FEES) AS total_fees FROM STUDENT GROUP BY NAME ORDER BY total_fees DESC;

执行上面代码，得到以下结果 -

sqlite> SELECT NAME, SUM(FEES) AS total_fees FROM STUDENT GROUP BY NAME ORDER BY NAME DESC;
Sqlsu|25000.0
Minsu|20000.0
Maxsu|29000.0
Linsu|75000.0
Javasu|18000.0
Avgsu|2000.0
sqlite>
sqlite> SELECT NAME, SUM(FEES) AS total_fees FROM STUDENT GROUP BY NAME ORDER BY total_fees DESC;
Linsu|75000.0
Maxsu|29000.0
Sqlsu|25000.0
Minsu|20000.0
Javasu|18000.0
Avgsu|2000.0
sqlite>