在 TiDB 中对一个 2 位浮点数字段求和，得到 8 位浮点数

Question

我从 infobright 转移了一些数据到 TiDB。我的 php 代码如下：

$sql='delete from xxx where xxx';
doQuery($sql);
$sql='insert into xxx (...)';
doQuery($sql);

我插入了48595条记录，但是它们的总和是8位浮点数。同时，该字段定义为 float(10,2):

mysql> SELECT COUNT(*) FROM adpay;
+----------+
| COUNT(*) |
+----------+
|    48595 | 
+----------+
1 row in set (0.28 sec)

mysql> SELECT SUM(t.spends) FROM (SELECT spends FROM adpay LIMIT 90000) t;
+---------------+
| SUM(t.spends) |
+---------------+
|   42583533.50 | 
+---------------+
1 row in set (0.37 sec)

mysql> SELECT SUM(spends) FROM adpay;
+-------------------+
| SUM(spends)       |
+-------------------+
| 42583533.50033116 | 
+-------------------+
1 row in set (0.35 sec)

mysql> show create table adpay;
...
CREATE TABLE `adpay` (
  `date` date NOT NULL DEFAULT '0000-00-00',
  `adname` varchar(50) NOT NULL DEFAULT '',
  `country` char(10) NOT NULL DEFAULT '',
  `pf` char(20) NOT NULL DEFAULT '',
  `paydate` date NOT NULL DEFAULT '0000-00-00',
  `num` int(10) DEFAULT NULL,
  `spends` float(10,2) NOT NULL,
  `todaynum` int(11) DEFAULT '0',
  `todayspends` float(10,2) DEFAULT '0.00',
  UNIQUE KEY `sdate` (`date`,`adname`,`country`,`pf`,`paydate`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci

请问是TiDB有问题，还是我做错了什么？任何建议表示赞赏。

更新中：

mysql> show create table test;
+-------+------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                               |
+-------+------------------------------------------------------------------------------------------------------------+
| test  | CREATE TABLE `test` (
  `t` float(10,2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin | 
+-------+------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)''

INSERT INTO test VALUES (1.11);
INSERT INTO test VALUES (1.111);


mysql> SELECT t,t-1.11 FROM test;
+------+----------------------------+
| t    | t-1.11                     |
+------+----------------------------+
| 1.11 | 0.000000014305114648394124 | 
| 1.11 | 0.000000014305114648394124 | 
| 1.11 | 0.000000014305114648394124 | 
+------+----------------------------+
3 rows in set (0.01 sec)

更新 2：

我只使用浮点数，没有指定数字。

mysql> show create table test1;
+-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------+
| test1 | CREATE TABLE `test1` (
  `t` float DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin | 
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> INSERT INTO test1 VALUES (1.11);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO test1 VALUES (1.111);
Query OK, 1 row affected (0.00 sec)

mysql> 
mysql> SELECT COUNT(*) FROM test1  WHERE t>ROUND(t, 2) ;
+----------+
| COUNT(*) |
+----------+
|        4 | 
+----------+
1 row in set (0.00 sec)

mysql> 
mysql> SELECT t,t-1.11 FROM test1;
+-------+----------------------------+
| t     | t-1.11                     |
+-------+----------------------------+
|  1.11 | 0.000000014305114648394124 | 
| 1.111 |      0.0009999418258666015 | 
|  1.11 | 0.000000014305114648394124 | 
| 1.111 |      0.0009999418258666015 | 
+-------+----------------------------+
4 rows in set (0.00 sec)

更新 3：

这个table有不同类型的字段，都是2位数。

然后我为每个字段插入 1.11 和 1.111。

在 TiDB 中只有 float 字段会将数据取为 8 位：

mysql> create table test2(f float(10,2),db double(10,2), de decimal(10,2));
Query OK, 0 rows affected (1.01 sec)

mysql> insert into test2(f,db,de) values(1.11,1.11,1.11);     
Query OK, 1 row affected (0.01 sec)

mysql> insert into test2(f,db,de) values(1.111,1.111,1.111);        
Query OK, 1 row affected, 1 warning (0.01 sec)

mysql> select *,f-1.11,db-1.11,de-1.11 from test2;
+------+------+------+----------------------------+---------+---------+
| f    | db   | de   | f-1.11                     | db-1.11 | de-1.11 |
+------+------+------+----------------------------+---------+---------+
| 1.11 | 1.11 | 1.11 | 0.000000014305114648394124 |       0 |       0 | 
| 1.11 | 1.11 | 1.11 | 0.000000014305114648394124 |       0 |       0 | 
+------+------+------+----------------------------+---------+---------+
2 rows in set (0.00 sec)

本地3个字段都可以 mysql 5.6:

mysql> create table test2(f float(10,2),db double(10,2), de decimal(10,2));
Query OK, 0 rows affected (0.29 sec)

mysql> insert into test2(f,db,de) values(1.11,1.11,1.11);
Query OK, 1 row affected (0.06 sec)

mysql> insert into test2(f,db,de) values(1.111,1.111,1.111);
Query OK, 1 row affected, 1 warning (0.04 sec)

mysql> select *,f-1.11,db-1.11,de-1.11 from test2;
+------+------+------+--------+---------+---------+
| f    | db   | de   | f-1.11 | db-1.11 | de-1.11 |
+------+------+------+--------+---------+---------+
| 1.11 | 1.11 | 1.11 |   0.00 |    0.00 |    0.00 |
| 1.11 | 1.11 | 1.11 |   0.00 |    0.00 |    0.00 |
+------+------+------+--------+---------+---------+
2 rows in set (0.00 sec)

Answer 1

您可以使用 ROUND 或 FORMAT 函数：

SELECT ROUND(SUM(spends), 2) FROM adpay;

Answer 2

问题是由函数 sum 和 minus 的类型推断不正确引起的。我们会尽快修复它。下次使用 TiDB 遇到问题可以在 https://github.com/pingcap/tidb/issues 中创建 issue。 ^_^

在 TiDB 中对一个 2 位浮点数字段求和，得到 8 位浮点数

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