显示带有负值的MySQL直方图？

对于负值，请使用reverse()以及concat()。让我们首先创建一个表-

create table DemoTable632 (
   histogramId int NOT NULL AUTO_INCREMENT PRIMARY KEY,histogramValue int,histogramImage text
);

使用插入命令在表中插入一些记录-

insert into DemoTable632(histogramValue) values(2);
insert into DemoTable632(histogramValue) values(3);
insert into DemoTable632(histogramValue) values(-6);
insert into DemoTable632(histogramValue) values(-5);

使用select语句显示表中的所有记录-

select *from DemoTable632;

这将产生以下输出-

+-------------+----------------+----------------+
| histogramId | histogramValue | histogramImage |
+-------------+----------------+----------------+
|           1 |              2 | NULL          |
|           2 |              3 | NULL          |
|           3 |             -6 | NULL          |
|           4 |             -5 | NULL          |
+-------------+----------------+----------------+
4 rows in set (0.00 sec)

这是对带有负值的直方图的查询-

SELECT histogramId, histogramValue, CONCAT(
      REVERSE(RPAD(REPEAT('*', IF(histogramValue<0,-histogramValue,0)), 100, ' ')),
      REPEAT('*',IF(histogramValue<0,0,histogramValue))
   )
AS histogramImage FROM DemoTable632 ORDER BY histogramId;

这将产生以下输出-

+-------------+----------------+----------------+
| histogramId | histogramValue | histogramImage |
+-------------+----------------+----------------+
|           1 | 2              | **             |
|           2 | 3              | ***            |
|           3 | -6             | ******         |
|           4 | -5             | *****          |
+-------------+----------------+----------------+
4 rows in set (0.00 sec)