REGEXP_LIKE Behavior
Often, the biggest problem with regular expressions is that those who use them sometimes don’t use them correctly. A great example occurs in the Oracle Database with the REGEXP_LIKE function. For example, some developer use the following to validate whether a string is a number but it only validates whether the first character is a number.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | DECLARE lv_input VARCHAR2(100); BEGIN /* Assign input value. */ lv_input := '&input'; /* Check for numeric string. */ IF REGEXP_LIKE(lv_input,'[[:digit:]]') THEN dbms_output.put_line('It''s a number.'); ELSE dbms_output.put_line('It''s a string.'); END IF; END; / |
When they test numbers it appears to works, it even appears to work when the test string start with number, but it fails with any string that starts with a character. That’s because the REGEXP_LIKE function on line 8 only checks the first character, but the following checks all the characters in the string.
8 | IF REGEXP_LIKE(lv_inputs(i),'[[:digit:]]{'||LENGTH(lv_inputs(i))||'}') THEN |
You can also fix it with the following non-Posix solution:
8 | IF REGEXP_LIKE(lv_input,'[[0-9]]') THEN |
You can add a collection to the program and use it to test single-digit, double-digit, and string with a leading integer. Save the program as test.sql and you can test three conditions with one call.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | DECLARE /* Declare the local collection type. */ TYPE inputs IS TABLE OF VARCHAR2(100); /* Declare a local variable of the collection type. */ lv_inputs INPUTS; BEGIN /* Assign the inputs to the collection variable. */ lv_inputs := inputs('&1','&2','&3'); /* Read through the collection and print whether it's an number or string. */ FOR i IN 1..lv_inputs.COUNT LOOP IF REGEXP_LIKE(lv_inputs(i),'[[:digit:]]{'||LENGTH(lv_inputs(i))||',}') THEN dbms_output.put_line('It''s a number.'); ELSE dbms_output.put_line('It''s a string.'); END IF; END LOOP; END; / |
You can run the test.sql program like this:
SQL> @test.sql 1 12 1a |
It prints:
It's a number. It's a number. It's a string. |
As always, I hope this helps those looking for a solution.
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