What's the purpose of varchar(0)
mysql, sql, sqldatatypes
Solution
It's not allowed per the SQL-92 standard, but permitted in MySQL. From the MySQL manual:
MySQL permits you to create a column of type `CHAR(0)`. This is useful primarily when you have to be compliant with old applications that depend on the existence of a column but that do not actually use its value. `CHAR(0)` is also quite nice when you need a column that can take only two values: A column that is defined as `CHAR(0)` NULL occupies only one bit and can take only the values `NULL` and `''` (the empty string).
Problem
I recently encountered a problem caused by a typo in the database creation script, whereby a column in the database was created as `varchar(0)` instead of `varchar(20)`. I expected that I would have gotten an error for 0-length string field, but I didn't. What is the purpose of `varchar(0)` or `char(0)` as I wouldn't be able to store any data in this column anyway.