mysql 中sum (if())与case

先来一个简单的sum

select sum(qty) as total_qty from inventory_product group by product_id

这样就会统计出全部product的qty.

可是很不幸，咱们的系统里面竟然有qty为负值。而我只想统计那些正值的qty，加上if function就能够了。 SQL为：

select sum(if(qty > 0, qty, 0)) as total_qty from inventory_product group by product_id

意思是若是qty > 0, 将qty的值累加到total_qty, 不然将0累加到total_qty.

如下是sum(if())的例子：

1 2 3 4 5 select sum( if( qty > 0, qty, 0)) as total_qty , sum( if( qty < 0, 1, 0 )) as negative_qty_count from inventory_product group by product_id

上面主要介绍sum (if())的定义，如下是关于数据库行列转换的一些方法整理，也是拷贝其余网友的博客的，作了一些删减。

现整理解法以下：

数据样本：

create table tx( id int primary key, c1 char(2), c2 char(2), c3 int );

insert into tx values (1 ,'A1','B1',9), (2 ,'A2','B1',7), (3 ,'A3','B1',4), (4 ,'A4','B1',2), (5 ,'A1','B2',2), (6 ,'A2','B2',9), (7 ,'A3','B2',8), (8 ,'A4','B2',5), (9 ,'A1','B3',1), (10 ,'A2','B3',8), (11 ,'A3','B3',8), (12 ,'A4','B3',6), (13 ,'A1','B4',8), (14 ,'A2','B4',2), (15 ,'A3','B4',6), (16 ,'A4','B4',9), (17 ,'A1','B4',3), (18 ,'A2','B4',5), (19 ,'A3','B4',2), (20 ,'A4','B4',5);

mysql> select * from tx; +----+------+------+------+ | id | c1 | c2 | c3 | +----+------+------+------+ | 1 | A1 | B1 | 9 | | 2 | A2 | B1 | 7 | | 3 | A3 | B1 | 4 | | 4 | A4 | B1 | 2 | | 5 | A1 | B2 | 2 | | 6 | A2 | B2 | 9 | | 7 | A3 | B2 | 8 | | 8 | A4 | B2 | 5 | | 9 | A1 | B3 | 1 | | 10 | A2 | B3 | 8 | | 11 | A3 | B3 | 8 | | 12 | A4 | B3 | 6 | | 13 | A1 | B4 | 8 | | 14 | A2 | B4 | 2 | | 15 | A3 | B4 | 6 | | 16 | A4 | B4 | 9 | | 17 | A1 | B4 | 3 | | 18 | A2 | B4 | 5 | | 19 | A3 | B4 | 2 | | 20 | A4 | B4 | 5 | +----+------+------+------+ 20 rows in set (0.00 sec)

mysql>

指望结果

+------+-----+-----+-----+-----+------+ |C1 |B1 |B2 |B3 |B4 |Total | +------+-----+-----+-----+-----+------+ |A1 |9 |2 |1 |11 |23 | |A2 |7 |9 |8 |7 |31 | |A3 |4 |8 |8 |8 |28 | |A4 |2 |5 |6 |14 |27 | |Total |22 |24 |23 |40 |109 | +------+-----+-----+-----+-----+------+

1. 利用SUM(IF()) 生成列 + WITH ROLLUP 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total

mysql> SELECT -> IFNULL(c1,'total') AS total, -> SUM(IF(c2='B1',c3,0)) AS B1, -> SUM(IF(c2='B2',c3,0)) AS B2, -> SUM(IF(c2='B3',c3,0)) AS B3, -> SUM(IF(c2='B4',c3,0)) AS B4, -> SUM(IF(c2='total',c3,0)) AS total -> FROM ( -> SELECT c1,IFNULL(c2,'total') AS c2,SUM(c3) AS c3 -> FROM tx -> GROUP BY c1,c2 -> WITH ROLLUP -> HAVING c1 IS NOT NULL -> ) AS A -> GROUP BY c1 -> WITH ROLLUP; +-------+------+------+------+------+-------+ | total | B1 | B2 | B3 | B4 | total | +-------+------+------+------+------+-------+ | A1 | 9 | 2 | 1 | 11 | 23 | | A2 | 7 | 9 | 8 | 7 | 31 | | A3 | 4 | 8 | 8 | 8 | 28 | | A4 | 2 | 5 | 6 | 14 | 27 | | total | 22 | 24 | 23 | 40 | 109 | +-------+------+------+------+------+-------+ 5 rows in set, 1 warning (0.00 sec)

1. 利用SUM(IF()) 生成列 + UNION 生成汇总行,并利用 IFNULL将汇总行标题显示为 Total mysql> select c1, -> sum(if(c2='B1',C3,0)) AS B1, -> sum(if(c2='B2',C3,0)) AS B2, -> sum(if(c2='B3',C3,0)) AS B3, -> sum(if(c2='B4',C3,0)) AS B4,SUM(C3) AS TOTAL -> from tx -> group by C1 -> UNION -> SELECT 'TOTAL',sum(if(c2='B1',C3,0)) AS B1, -> sum(if(c2='B2',C3,0)) AS B2, -> sum(if(c2='B3',C3,0)) AS B3, -> sum(if(c2='B4',C3,0)) AS B4,SUM(C3) FROM TX -> ; +-------+------+------+------+------+-------+ | c1 | B1 | B2 | B3 | B4 | TOTAL | +-------+------+------+------+------+-------+ | A1 | 9 | 2 | 1 | 11 | 23 | | A2 | 7 | 9 | 8 | 7 | 31 | | A3 | 4 | 8 | 8 | 8 | 28 | | A4 | 2 | 5 | 6 | 14 | 27 | | TOTAL | 22 | 24 | 23 | 40 | 109 | +-------+------+------+------+------+-------+ 5 rows in set (0.00 sec)

2. 利用SUM(IF()) 生成列,直接生成结果再也不利用子查询 mysql> select ifnull(c1,'total'), -> sum(if(c2='B1',C3,0)) AS B1, -> sum(if(c2='B2',C3,0)) AS B2, -> sum(if(c2='B3',C3,0)) AS B3, -> sum(if(c2='B4',C3,0)) AS B4,SUM(C3) AS TOTAL -> from tx -> group by C1 with rollup ; +--------------------+------+------+------+------+-------+ | ifnull(c1,'total') | B1 | B2 | B3 | B4 | TOTAL | +--------------------+------+------+------+------+-------+ | A1 | 9 | 2 | 1 | 11 | 23 | | A2 | 7 | 9 | 8 | 7 | 31 | | A3 | 4 | 8 | 8 | 8 | 28 | | A4 | 2 | 5 | 6 | 14 | 27 | | total | 22 | 24 | 23 | 40 | 109 | +--------------------+------+------+------+------+-------+ 5 rows in set (0.00 sec)

3. 动态，适用于列不肯定状况，

mysql> SET @EE=''; mysql> SELECT @EE:=CONCAT(@EE,'SUM(IF(C2='',C2,''',',C3,0)) AS ',C2,',') FROM (SELECT DISTINCT C2 FROM TX) A;

mysql> SET @QQ=CONCAT('SELECT ifnull(c1,'total'),',LEFT(@EE,LENGTH(@EE)-1),' ,SUM(C3) AS TOTAL FROM TX GROUP BY C1 WITH ROLLUP'); Query OK, 0 rows affected (0.00 sec)

mysql> PREPARE stmt2 FROM @QQ; Query OK, 0 rows affected (0.00 sec) Statement prepared

mysql> EXECUTE stmt2; +--------------------+------+------+------+------+-------+ | ifnull(c1,'total') | B1 | B2 | B3 | B4 | TOTAL | +--------------------+------+------+------+------+-------+ | A1 | 9 | 2 | 1 | 11 | 23 | | A2 | 7 | 9 | 8 | 7 | 31 | | A3 | 4 | 8 | 8 | 8 | 28 | | A4 | 2 | 5 | 6 | 14 | 27 | | total | 22 | 24 | 23 | 40 | 109 | +--------------------+------+------+------+------+-------+ 5 rows in set (0.00 sec)

5.使用case，

　　

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 SELECT ifnull(c1,'total')`, MAX( CASE WHEN c2= 'B1' THEN C3 END ) AS B1, MAX( CASE WHEN c2= 'B2' THEN C3 END ) AS B2, MAX( CASE WHEN c2= 'B3' THEN C3 END ) AS B3, MAX( CASE WHEN c2= 'B4' THEN C3 END ) AS B4 FROM tx GROUP BY c1 　　

其实数据库中也能够用 CASE WHEN / DECODE 代替 IF