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I’ve bumped into a lot of VARCHAR(1) fields in a database I’ve recently had to work with. I rolled my eyes: obviously the designer didn’t have a clue. But maybe I’m the one who needs to learn something. Is there any conceivable reason to use a VARCHAR(1) data type rather than CHAR(1)? I would think that the RDMS would convert the one to the other automatically.
The database is MS SQL 2K5, but evolved from Access back in the day.
Yes there is sense to it.
Easier for it to be definable in the language. It is consistent and easier to define varchar to allow 1-8000 than to say it needs to be 2+ or 3+ to 8000.
The VARying CHARacter aspect of VARCHAR(1) is exactly that. It may not be optimal for storage but conveys a specific meaning, that the data is either 1 char (classroom code) or blank (outside activity) instead of NULL (unknown/not-yet-classified).
Storage plays very little part in this – looking at a database schema for CHAR(1), you would almost expect that it must always have a 1 char value, such as credit cards must have 16 digits. That is simply not the case with some data where it can be one or optionally none.
There are also differences to using VARCHAR(1) vs CHAR(1)+NULL combination for those who say tri-state [ 1-char | 0-char | NULL ] is completely useless. It allows for SQL statements like:
which would otherwise be more difficult if you use char(1)+NULL, which can convey the same information but has subtle differences.