Oracle if-else query to check table exist otherwise show a message? - database

Question

When i am running below query first time its working but after again i am going to run this query i am getting exception
Select count(*) into rec from all_tables where table_name='DefaultTable';
if(rec=1) then
CREATE TABLE DefaultTable(
Code INT NOT NULL,
Code1 INT NOT NULL,
ResultCode INT NOT NULL,
CONSTRAINT DefaultTable_PK PRIMARY KEY(Code,Code1)
);
else
PRMOPT DefaultTable Already Exist //To print in Console
end if;
Can anyone tell what i am doing wrong? and what all i am doing wrong to write the above query ?
Error starting at line 2 in command:
if(rec=1) then
Error report:
Unknown Command
Error starting at line 3 in command:
CREATE TABLE DefaultTable(
Code INT NOT NULL,
Code1 INT NOT NULL,
ResultCode INT NOT NULL,
CONSTRAINT DefaultTable_PK PRIMARY KEY(Code,Code1)
Error at Command Line:3 Column:14
Error report:
SQL Error: ORA-00955: name is already used by an existing object
00955. 00000 - "name is already used by an existing object"
*Cause:
*Action:
Error starting at line 16 in command:
else
Error report:
Unknown Command
Error starting at line 17 in command:
PRMOPT Table Already Exist
Error report:
Unknown Command
Error starting at line 18 in command:
end if
Error report:
Unknown Command

Answer 1

Well, as I understand the author is trying to do it in one sql query. But in Oracle you can not use IF statement in simple sql. Moreover, even if you use PL/SQL the DDL statements are not allowed to be directly invoked from PL/SQL code, so you should use dynamic SQL. I think, the following script will do what you want:
DECLARE
rec NUMBER;
BEGIN
SELECT COUNT(*) INTO rec FROM all_tables WHERE table_name='DEFAULTTABLE';
IF (rec=0) THEN
EXECUTE IMMEDIATE 'CREATE TABLE DefaultTable(
Code INT NOT NULL,
Code1 INT NOT NULL,
ResultCode INT NOT NULL,
CONSTRAINT DefaultTable_PK
PRIMARY KEY(Code,Code1,ResultCode)
)';
ELSE
dbms_output.put_line('DefaultTable Already Exist');
END IF;
END;
Please, note that in order to see the messages printed via dbms_output, you should execute:
SET SERVEROUTPUT ON;

Answer 2

If you read the error message you will notice it says:
ORA-00955: name is already used by an existing object
This means you are trying to create a table that already exists. That explains why it runs the first time and not any more after that.
Check the entries in all_tables and you will find that Oracle creates tablenames in uppercase. So check for 'DEFAULTTABLE'.