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I'm trying to generate a little more performance from a particular table full of hundreds of thousands of rows. There are a few VARCHAR fields that I'm converting to CHAR.

I'm aware that I won't get the speed benefit of switching to fixed length CHAR fields if any variable length rows exist in my table. However, when I search for a list of all fixed length–or variable length–field types for MySQL, I come up short. My table contains a few DECIMAL and DATETIME fields. I'm somewhat sure the latter is fixed, but the former? Not sure.

Does anyone have a definitive list?

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2 Answers 2

up vote 1 down vote accepted

See from the official MySQL documentation: section Data Type Storage Requirements has it all.

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Great. VARCHAR, VARBINARY, and the BLOB and TEXT types are variable-length types. I'm assuming that's it? If so, excellent. –  Stephen Nov 8 '10 at 16:09
    
Yep, those are all variable types. –  Janne Pikkarainen Nov 8 '10 at 16:31
    
Not to beat a dead horse, but: "those are all variable types" or "those are all of the variable types" ? I want to make sure I'm not missing any. ;) –  Stephen Nov 8 '10 at 17:15
    
@Stephen: Those are all of the variable types that I know of. But be warned: if you truly want to be sure you don't miss anything, then you'll also need to learn about how different MySQL storage engines (MyISAM, InnoDB ...) handle these things. –  Janne Pikkarainen Nov 8 '10 at 17:18

The length of a CHAR column is fixed to the length that you declare when you create the table. The length can be any value from 0 to 255

Values in VARCHAR columns are variable-length strings. The length can be specified as a value from 0 to 65,535

I always thought it was better to use VARCHAR.. as the variable length is better than the static CHAR

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Right, VARCHAR is nice. But if all of your columns are fixed length, MySQL can burn through your queries faster. –  Stephen Nov 8 '10 at 16:06

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