About Case Sensitivity

Article by Rampant author Laurent Schneider

SQL is a case insensitive language. That means, you can write any SQL statement in uppercase or lowercase.

SQL> SELECT DUMMY FROM DUAL;D
-
X 

SQL> select dummy from dual;
D
-
X

Some formatters like Toad and some courseware like Skillsoft E-Learning advise to use UPPERCASE for commands and lowercase for tables and columns. 

/* Formatted on 2008/09/19 10:00
(Formatter Plus v4.8.8) */
SELECT dummy
  FROM DUAL;

Well, Toad decided to put DUAL in uppercase. Anyway, this is no authority, define your own guideline and stick to it. If you use TOAD a lot, it is maybe OK to use lowercase for non-keywords.

The column dummy is actually the uppercase “DUMMY” column of “DUAL”. Putting double quotes around a column of table makes it case sensitive, so “DUMMY” is not “dummy”.

SQL> select "dummy" from "dual";
select "dummy" from "dual"
                    *
Error at line 1
ORA-00942: table or view does not exist 

SQL> SELECT "DUMMY" FROM "DUAL";
D
-
X

OK, something very bad about Toad formatter is (at least the version I am using) that it considers unquoted password to be case insensitive. Which is wrong. The password, in 11g, is case sensitive, even when not in double quotes. Therefore, be sure to put the right case when creating scripts and do not format your CREATE USER statements with Toad or use double quotes for disambiguation! 

SQL> ALTER USER scott IDENTIFIED BY BIG;
User altered.
SQL> connect scott/BIG
Connected.
SQL> /* Formatted on 2008/09/19 10:17 (Formatter Plus v4.8.8) */
SQL> ALTER USER scott IDENTIFIED BY big;
SQL> connect scott/BIG
ERROR:
ORA-01017: invalid username/password; logon denied
Warning: You are no longer connected to ORACLE.