MySQL Bugs: #29930: Incorrect docs of MYSQL

Bug #29930	Incorrect docs of MYSQL_FIELD
Submitted:	20 Jul 2007 12:13	Modified:	23 Jan 2008 18:45
Reporter:	Andrey Hristov	Email Updates:
Status:	Not a Bug	Impact on me:	None
Category:	MySQL Server: C API (client library)	Severity:	S3 (Non-critical)
Version:	5.0 bk, 5.1 bk	OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
http://dev.mysql.com/doc/refman/5.0/en/c-api-datatypes.html :
# unsigned long length

The width of the field. This corresponds to the display length, in bytes.

However, this is not true for BIT. For BIT the length on disk in bytes is sent.

[14:58:08] andrey@lmy004:~/dev/php6> mysql --column-type-info -h 127.0.0.1 test
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.1.21-beta-debug-log Source distribution

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> select * from bittable;
Field   1:  `a`
Catalog:    `def`
Database:   `test`
Table:      `bittable`
Org_table:  `bittable`
Type:       BIT
Collation:  binary (63)
Length:     12
Max_length: 0
Decimals:   0
Flags:      UNSIGNED

0 rows in set (0.00 sec)

mysql> prepare xyz from "select * from bittable";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> execute xyz;
Field   1:  `a`
Catalog:    `def`
Database:   `test`
Table:      `bittable`
Org_table:  `bittable`
Type:       BIT
Collation:  binary (63)
Length:     12
Max_length: 0
Decimals:   0
Flags:      UNSIGNED

0 rows in set (0.00 sec)

How to repeat:
See statements above.

Thank you for the report.

Verified as described.

This bug report is either wrong, or it is a server bug. MYSQL_FIELD::length should *always* be the display length of the field, regardless of type. Anything else will break things like Connector/ODBC.

Fixing this for MYSQL_FIELD::length was Bug #13601.

Here's what I get with 5.1.20:

mysql> create table t1 (a bit(3));
Query OK, 0 rows affected (0.02 sec)

mysql> insert into t1 values (b'001'), (b'100');
Query OK, 2 rows affected (0.03 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> select * from t1
    -> ;
Field   1:  `a`
Catalog:    `def`
Database:   `test`
Table:      `t1`
Org_table:  `t1`
Type:       BIT
Collation:  binary (63)
Length:     3
Max_length: 1
Decimals:   0
Flags:      UNSIGNED 

+------+
| a    |
+------+
|     | 
|     | 
+------+
2 rows in set (0.00 sec)

mysql> prepare xyz from "select * from t1";
Query OK, 0 rows affected (0.00 sec)
Statement prepared

mysql> execute xyz;
Field   1:  `a`
Catalog:    `def`
Database:   `test`
Table:      `t1`
Org_table:  `t1`
Type:       BIT
Collation:  binary (63)
Length:     3
Max_length: 1
Decimals:   0
Flags:      UNSIGNED 

+------+
| a    |
+------+
|     | 
|     | 
+------+
2 rows in set (0.00 sec)

As agreed by Andrey, this is not a bug. The documentation is correct, and the output of the server agrees with this.