Inserting NULL value to a double data type MySQL Python

问题

I have a table. This is the create statement.

   CREATE TABLE `runsettings` (
  `runnumber` mediumint(9) NOT NULL,
  `equipment` varchar(45) NOT NULL,
  `wafer` varchar(45) NOT NULL,
  `settingname` varchar(100) NOT NULL,
  `float8value` double DEFAULT NULL,
  `apcrunid` varchar(45) DEFAULT NULL,
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `intvalue` int(11) DEFAULT NULL,
  `floatvalue` float DEFAULT NULL,
  `Batch` varchar(45) DEFAULT NULL,
  `IndexNum` smallint(6) DEFAULT '1',
  `stringvalue` mediumtext,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=1056989 DEFAULT CHARSET=latin1;

This is my insert statement :

import mysql.connector

cnx = mysql.connector.connect(user='test',
                                password ='test',host='0.0.0.1',
                              database='test')


vallist = [(471285, u'CT19', 7, u'271042', u'Etch Time Min', None, None, None),
           (471285, u'CT19', 7, u'00000', u'Etch Time Min', None, None, 'None')]


cursor = cnx.cursor()
# ss = 

cursor.executemany("INSERT INTO runsettings (apcrunid,equipment,runnumber,wafer,settingname,intvalue,floatvalue,float8value) VALUES (%s,%s,%s,%s,%s,%s,%s,%s)",vallist)
cnx.commit()

So I try to insert these values .

vallist = [471285, u'CT19', 7, u'271042', u'Etch Time Min', None, None, None,
           471285, u'CT19', 7, u'00000', u'Etch Time Min', None, None, 'None']

This is getting inserted. Result on DB But when the list value is this one (difference is the string 'None' gets evaluated first):

vallist = [471285, u'CT19', 7, u'271042', u'Etch Time Min', None, None, 'None', 
           471285, u'CT19', 7, u'271042', u'Etch Time Min', None, None, None]

It gives out the truncated error.

Data truncated for column 'float8value' at row 2

How come when the row that contains None is the first on the list it doesn't give out the same truncated error on the first list?

回答1:

This is not entirely suprising. In the first instance you are inserting the python predefined constant None

The sole value of types.NoneType. None is frequently used to represent the absence of a value, as when default arguments are not passed to a function.

That equates to SQL NULL. In the second instance you are inserting a String called 'None' into the table. These two are very different. If you insert a string into a double or float field you will see all kinds of errors, most often, the exact one you have seen.

in the first instance it works because you have declared :

 `float8value` double DEFAULT NULL,

This accepts NULL and None is in the 8th place in your values list. When lots of different parameters are being used, it's always a good idea to use named parameters so that it's obvious at a glance what's being bound to each column.

Updates:

After running your code, the only conclusion that can be reached is that you have found a bug, by using print(cursor.statement) it's possible to discover that the executed query is.

INSERT INTO runsettings (apcrunid,equipment,runnumber,wafer,settingname,intvalue,floatvalue,float8value) 
VALUES (471285,'CT19',7,'271042','Etch Time Min',NULL,NULL,NULL),
       (471285,'CT19',7,'00000','Etch Time Min',NULL,NULL,'None')

This does not produce an error, but if you erase the first set of values the error is indeed produced. My recommendation is to file a bug report

来源：https://stackoverflow.com/questions/39629823/inserting-null-value-to-a-double-data-type-mysql-python

标签

python

mysql

prepared-statement