问题
I have a very simple rating system in my database where each rating is stored as an enum('1','-1'). To calculate the total I tried using this statement:
SELECT SUM(CONVERT(rating, SIGNED)) as value from table WHERE _id = 1
This works fine for the positive 1 but for some reason the -1 are parsed out to 2's.
Can anyone help or offer incite?
Or should I give up and just change the column to a SIGNED INT(1)?
回答1:
Yes, I'd suggest to change the type of the column. The issue becomes clear when you read the doc about enum type (which strongly recommends not to use numbers as enumeration values!) - the index of the enum item is returned, not the enum value itself.
回答2:
this is what you want
select enum+0 as enum
回答3:
This conversion to int in MySQL for enum is only possible:
CAST(CAST(`rating` AS CHAR) AS SIGNED) as value from table WHERE _id = 1
回答4:
use
SELECT SUM( IF( columnname >0, CAST( columnname AS CHAR ) , NULL ) ) AS vals
FROM `tableName`
回答5:
Ok guys,
Just had a bit of a mere of a time with this one. I learned that i shouldn't use ENUMs where integers are the values. However We had years worth of data and i couldn't alter the database.
This bad boy worked (turning it into a character, then into a signed int).
CAST(CAST(`rating` AS CHAR) AS SIGNED) as value from table WHERE _id = 1
来源：https://stackoverflow.com/questions/6803641/issue-mysql-converting-enum-to-int