Trimming both 0 and trailing/leading spaces doesn't give results - MySQL

Question

I have the below situation in the database where accounts could have leading 0 and white spaces.

If I use TRIM(TRIM(LEADING '0' FROM account_ref)) as account_ref_trimmed , I get:

Question, is it correct to put trim inside the trim? Secondly, why in row 5, there is still a leading 0?

Answer 1

Trim the spaces and then the zeroes:

TRIM(LEADING '0' FROM TRIM(account_ref))

When you try to trim the zeroes first, any values that have spaces at the beginning and then zeroes will only be trimmed off of spaces.
As for your question about precedence it is indicated by the nested parentheses.