Oracle REGEXP_INSTR() and “a-z” character range doesn't match as expected

Question

I want to use REGEXP_INSTR() within an oracle database to check for lower/uppercase characters. I\'m aware of [:upper:] and [:lower:] POSI

Answer 1

The reason for the behavior is the collation rules. See the NLS_SORT documentation:

• If the value is BINARY, then the collating sequence for ORDER BY queries is based on the numeric value of characters (a binary sort that requires less system overhead).
  
• If the value is a named linguistic sort, sorting is based on the order of the defined linguistic sort. Most (but not all) languages supported by the NLS_LANGUAGE parameter also support a linguistic sort with the same name.

Set the NLS_SORT to BINARY so that the [A-Z] could be parsed in the same order as in the ASCII table,

alter session set nls_sort = 'BINARY'

Then, you will get consistent results.

See the online demo.