CODEWITHSUNDEEP
pythonmysqlmysql-pythontemp-tables
satoru
satoru

Reputation: 33225

MySQLdb return `Decimal` for a `sum` of `INT`

This is the table definition I use to reproduce the issue:

create table test_sum_type 
(
  kind char(1) not null,
  n tinyint not null
);

Test data:

+------+---+                                                                                                                                                                                                    
| kind | n |                                                                                                                                                                                                    
+------+---+                                                                                                                                                                                                    
| A    | 1 |                                                                                                                                                                                                    
| B    | 1 |                                                                                                                                                                                                    
| A    | 2 |                                                                                                                                                                                                    
+------+---+

Query using MySQLdb:

In [32]: cur.execute("select kind, sum(n) from test_sum_type group by kind")                                                                                                                                    
Out[32]: 2L                                                                                                                                                                                                     

In [33]: cur.fetchall()                                                                                                                                                                                         
Out[33]: (('A', Decimal('3')), ('B', Decimal('1')))                                                                                                                                                             

In [34]: cur.execute("select kind, n from test_sum_type")                                                                                                                                                       
Out[34]: 3L                                                                                                                                                                                                     

In [35]: cur.fetchall()                                                                                                                                                                                         
Out[35]: (('A', 1), ('B', 1), ('A', 2))

As you can see, the resulting column is a Decimal when I use sum.

I've looked into the source code of MySQLdb, there're only two field types set up to be converted to Decimal by default: DECIMAL and NEWDECIMAL.

What may be the reason of this? Is there any way to check the schema of some temporary table used in a specific query?

Upvotes: 4

Views: 6802

Answers (1)

peterm
peterm

Reputation: 92785

It's by design in MySql.

GROUP BY (Aggregate) Functions
The SUM() and AVG() functions return a DECIMAL value for exact-value arguments (integer or DECIMAL), and a DOUBLE value for approximate-value arguments (FLOAT or DOUBLE). (Before MySQL 5.0.3, SUM() and AVG() return DOUBLE for all numeric arguments.)

If you need to return an INT then CAST it.

SELECT kind, CAST(SUM(n) AS SIGNED) n 
  FROM table1 
 GROUP BY kind

Here is SQLFiddle demo

Upvotes: 10

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