Oracle's lack of a Bit datatype for table columns

Use a CHAR(1), and a constraint to allow only 1 and 0.

...

col CHAR(1),
CONSTRAINT cons_atable_col1 CHECK (col1 IN ('1','0'))

I'm not an English native so I tend to use either 1 and 0 or '1' and '0'. Using 'Y' and 'N' make little sense if you aren't coding in English (yes, native language coding does exist). Using 'SI' and 'NO' or 'S' and 'N' doesn't look professional (just like naming variables with accented letters). Ones and zeroes, on the contrary, are pretty standard if you've coded in C, PHP or JavaScript. In any case, I always add the appropriate constraint to disallow any other character. Apart from subjective issues, I don't think there're noticeable performance gain in choosing CHAR or NUMBER. I like numbers a little more because I don't need to quote them :)

I agree it's a glaring omission but I've read seriously heated discussions on the subject in some Oracle forums; it's a kind of religious issue. Some claim that booleans belong to application data types and have no place in the database core. Honestly, I believe it's one of those We Have Been So Long Without It That We Had Better Say It Was On Purpose things.

By the way, MySQL has a BOOLEAN type but it's a synonym for TINYINT(1) so it eventually equals to 1 and 0; which is fine, because it also has the constants TRUE and FALSE that evaluate to 1 and 0.

I prefer char(1) over number(1), since with some reasonable choice of characters, it is obvious which character has which boolean meaning.

Of course you should fight all the different varations, choose one and ensure it's use by putting check constraints on the columns.

Although it probably is to late in your case, generating the schema from another tool often takes care at least of the consistency issue. I personally prefer hibernate for this purpose, but that is very situation specific.

And of course that is a glaring obmission. To make it worse, PL/SQL has a boolean, but you can't use it in SQL statements.