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Mike Hillyer is a Technical Writer for MySQL AB and lives in Alberta, Canada.

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Visual Basic / MySQL Datatypes

By Mike Hillyer

Visual Basic can be very loose with it's data types. If you want to avoid worrying about which type of data is coming from your database, you can simply not specify a datatype when you declare a variable, which defaults the datatype to variant. The variant should be avoided whenever possible, as it can be very CPU and memory intensive. Below is a table of the different MySQL and VB6 datatypes and how they correlate. One warning: often the VB6 datatype can hold a larger value than the MySQL equivalent (marked with a * in the notes section), in these situations you need to take care that the VB6 value is not to large to fit in the MySQL column. While you will not necesscarily get an error (you get a warning in the mysql client), data corruption will occur.

MySQL Datatype	Length	VB6 Datatype	Length	Notes
TINYINT	-128 to 127	integer	-32,768 to 32,767	*
TINYINT UNSIGNED	0 to 255	byte	0 to 255
SMALLINT	-32,768 to 32,767	integer	-32,768 to 32,767
SMALLINT UNSIGNED	0 to 65,535	long	-2,147,483,647 to 2,147,483,647	*
MEDIUMINT	-8,388,608 to 8,388,607	long	-2,147,483,647 to 2,147,483,647	*
MEDIUMINT UNSIGNED	0 to 16,777,215	long	-2,147,483,647 to 2,147,483,647	*
INT	-2,147,483,647 to 2,147,483,647	long	-2,147,483,647 to 2,147,483,647
INT UNSIGNED	0 to 4,294,967,295	double	64 Bit	1*
BIGINT	64 Bit	N/A	N/A	2
FLOAT	32 Bit Floating Point	single	32 Bit Floating Point
DOUBLE	64 Bit Floating Point	double	64 Bit Floating Point
DECIMAL	Variable Floating Point	double	64 Bit Floating Point	3*
CHAR	1 to 255 Characters	string	1 to Approx. 2,000,000,000 Characters	*
VARCHAR	1 to 255 Characters	string	1 to Approx. 2,000,000,000 Characters	*
TINYTEXT	1 to 255 Characters	string	1 to Approx. 2,000,000,000 Characters	*
TEXT	1 to 65535 Characters	string	1 to Approx. 2,000,000,000 Characters	4*
MEDIUMTEXT	1 to 16,777,215 Characters	string	1 to Approx. 2,000,000,000 Characters	4*
LONGTEXT	1 to 4,294,967,295 Characters	N/A	N/A	5
all BLOB types	1 to 4,294,967,295 Bytes	Variant	Varies	6
DATE	Date without Time	date	Date and Time value	*
DATETIME	Date and Time	date	Date and Time value
TIMESTAMP	Date and Time	date	Date and Time value
TIME	Time	date	Date and Time value	*
YEAR	Year	integer	-32,768 to 32,767	*
ENUM	Enumeration of Value Set	string	1 to Approx. 2,000,000,000 Characters	*
SET	Set of Values	string	1 to Approx. 2,000,000,000 Characters	*

Notes:

1) There is no such thing as a 32 bit unsigned integer in VB, so data must be stored in a double, which is actually a floating-point datatype, therefore, be careful to make sure that any value that you will be passing to MySQL is rounded off before you post it. The use of an UNSIGNED INT with VB6 is not reccomended, but you may have some luck with the larger integers of VB.NET.

2) BIGINT cannot be used with ADO, as it will cause errors, you can use the MyODBC option of 16384 (convert BIGINT to INT) to make them funnel down, but from what I understand your BIGINT is then limited to the size of an INT anyway. If a BIGINT is brought into a long, you will be ok up to the limit if the long datatype, after which your data will be corrupted.

3) DECIMAL can be passed to different VB6 Datatypes depending on how you define the DECIMAL column when creating the table. I personally would recommend staying away from the DECIMAL type, as it takes 1 byte per digit for storage, you are better off using the appropriate numeric type.

4) If you have trouble loading TEXT and MEDIUMTEXT values from a recordset, make sure your max_allowed_packet parameter in MySQL is set appropriately high. I have been able to load text from a MEDIUMTEXT object up to the max_allowed_packet limit set in my server.

5) LONGTEXT data cannot be held in a string, and would need to be treated as a BLOB and written directly to a file using the BLOB handling methods. If using the stream object, change the stream type to adTypeText instead of adTypeBinary.

6) All blob data must be passed using either the getchunk/appendchunk method, or the ADO stream object. The variant in this case becomes a byte array, and cannot be handled directly by VB6.