Question

我在MySQL表中有下一列，十进制（20,2）：

将该十进制值更新为：

的最简单方法是什么

如果我将列更改为十进制（20,3），我会得到下一个数字： 10.010,10.090 ... 10.990等。每个号码必须是唯一的。如果MySQL不能这样做，如何使用php？

Answer 1

你可以使用这样的查询。首先将您的字段设置为十进制（20,3）：分两步完成：首先添加1以防止重复输入。第二减1

第一步

UPDATE youtTable
set val = 
  CAST(val as unsigned integer) +1 
  + (val - CAST(val as unsigned integer)) / 10;

第二步

UPDATE youtTable
set val = val -1;

但如果您先更改最小的数字，也可以使用一个查询执行此操作：

UPDATE yourTable
set val = 
  CAST(val as unsigned integer) 
  + (val - CAST(val as unsigned integer)) / 10
ORDER by val ASC;

<强>样品

mysql> SELECT  CAST(10.19 as unsigned integer) + (10.19 - CAST(10.19 as unsigned integer)) / 10;
+----------------------------------------------------------------------------------+
| CAST(10.19 as unsigned integer) + (10.19 - CAST(10.19 as unsigned integer)) / 10 |
+----------------------------------------------------------------------------------+
|                                                                        10.019000 |
+----------------------------------------------------------------------------------+
1 row in set (0,00 sec)

mysql>

Answer 2

我会按以下方式执行此操作

首先取回桌子。
然后添加一个带小数（20,3）
然后通过执行一些字符串操作来使用旧列中的值更新列。
删除旧列
重命名新列。

这是一个测试用例

mysql> create table test (no decimal(20,2));
Query OK, 0 rows affected (0.20 sec)

mysql> insert into test values('10.01'),('10.09'),('10.10'),('10.11'),('10.19'),('10.99');
Query OK, 6 rows affected (0.03 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> select * from test;
+-------+
| no    |
+-------+
| 10.01 |
| 10.09 |
| 10.10 |
| 10.11 |
| 10.19 |
| 10.99 |
+-------+
6 rows in set (0.00 sec)

mysql> alter table test add column no_new decimal(20,3);
Query OK, 0 rows affected (0.38 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from test;
+-------+--------+
| no    | no_new |
+-------+--------+
| 10.01 |   NULL |
| 10.09 |   NULL |
| 10.10 |   NULL |
| 10.11 |   NULL |
| 10.19 |   NULL |
| 10.99 |   NULL |
+-------+--------+
6 rows in set (0.00 sec)

然后

mysql> update test set no_new = concat(substring_index(no,'.',1),'.',concat('0',substring_index(no,'.',-1)));
Query OK, 6 rows affected (0.05 sec)
Rows matched: 6  Changed: 6  Warnings: 0

mysql> select * from test;
+-------+--------+
| no    | no_new |
+-------+--------+
| 10.01 | 10.001 |
| 10.09 | 10.009 |
| 10.10 | 10.010 |
| 10.11 | 10.011 |
| 10.19 | 10.019 |
| 10.99 | 10.099 |
+-------+--------+
6 rows in set (0.00 sec)

mysql> alter table test drop column no;
Query OK, 0 rows affected (0.36 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table test change no_new no decimal(20,3);
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> select * from test ;
+--------+
| no     |
+--------+
| 10.001 |
| 10.009 |
| 10.010 |
| 10.011 |
| 10.019 |
| 10.099 |
+--------+
6 rows in set (0.00 sec)

Answer 3

 *****Using MySql*****

 --> SELECT FORMAT('COLUMN NAME',DECIMAL VALUE);

  *****FOR EXAMPLE:*****

 --> SELECT FORMAT(NO,3);


         *****QUERY*****

      Create table '#test1'
      (no decimal(5,3));

 insert into '#test1' values
 ('10.01'),
 ('10.09'),
 ('10.10'),
 ('10.11'),
 ('10.19'),
 ('10.99');

        ****RESULT****
           [![DEMO IMAGE][1]][1]

     [1]: https://i.stack.imgur.com/AzZpB.jpg

更新小数列以允许小数点后的更多位数

3 个答案: