I think in order to do this, I have to convert the BIGINT to a varchar first, but how?

Thanks for your help!

if you are cocerned about how many bytes a bigint takes, it is always 8 and it can represent a number with 19 digits.

I have a column in a table that is of type BIGINT. However the values doesnt always have the same number of digits, it can contain 11 or 13 digits (e.g. 91310140001). I need to be able to distinguish which rows contain 11 or 13 digits, which is why I want to find the length.

That reminds me of a guy who did this in java:
Don't they teach arithmetics in universities anymore?

Will this work? SELECT LENGTH(STRIP(CHAR(YOUR_BIGINT_COLUMN))) ...

When you say number of digits, I assume you are excluding leading zeros?

If that is the case, any value > 99999999999 must have more than 11 "digits" (as you call them).

To distinguish them, you can use the case statement, where clause, if statement in a proc or function, etc.

consider using:

FLOOR(LOG10(your_column))+1