EXECUTE IMMEDIATE Temp table in oracle does not get created ORA-00942

Question

Based on this answer I was trying to create temp table, however I am getting exception ORA-00942:table or view does not exist I would assume there is something wrong with 'CREATE OR REPLACE GLOBAL TEMPORARY TABLE TempQandA(column1 number) ON COMMIT PRESERVE ROWS' statement, it fails on insert into TempQandA(column1) VALUES (1);.
Please find SQL statement below.

DECLARE 
TransactioDetailId numeric := 3132;
HomePhoneNumber varchar(20);
MobileNumber varchar(20);
Email varchar(20);
whatever varchar(20);
BEGIN
EXECUTE IMMEDIATE 'CREATE OR REPLACE GLOBAL TEMPORARY TABLE TempQandA(column1 number) ON COMMIT PRESERVE ROWS';

        BEGIN
        SELECT contactvalue into HomePhoneNumber  FROM customercontact CC
         inner join TRANSACTIONMAIN tm on tm.customerid = CC.customerid
         inner join transactiondetail td on td.transactionid = tm.transactionid
         where contacttypeid = 2 and td.transactiondetailid = TransactioDetailId;
         EXCEPTION
         WHEN NO_DATA_FOUND THEN
         HomePhoneNumber := NULL;
                         begin
                         SELECT  contactvalue into MobileNumber  FROM customercontact CC
                         inner join TRANSACTIONMAIN tm on tm.customerid = CC.customerid
                         inner join transactiondetail td on td.transactionid = tm.transactionid
                         where contacttypeid = 3 and td.transactiondetailid = TransactioDetailId;
                         EXCEPTION
                         WHEN NO_DATA_FOUND THEN
                         MobileNumber := NULL;
                                      begin
                                      SELECT  contactvalue into Email  FROM customercontact CC
                                      inner join TRANSACTIONMAIN tm on tm.customerid = CC.customerid
                                      inner join transactiondetail td on td.transactionid = tm.transactionid
                                      where contacttypeid = 1 and td.transactiondetailid = TransactioDetailId;
                                      EXCEPTION
                                      WHEN NO_DATA_FOUND THEN
                                      Email := NULL;

                                            begin
                                            insert into TempQandA(column1) VALUES (1);
                                             end;
                                     end;
                     end;
         end;
END;

Answer 1

You dynamically create the GTT, so your INSERT too should be dynamic..

Note that, PL/SQL validates every static query before even executing it. Thats why you get ORA-942 Table or view doesn't exist error even at compilation time!

So, to escape this semantic check, we have to make the call dynamic.

    BEGIN
    EXECUTE IMMEDIATE 'CREATE GLOBAL TEMPORARY TABLE TempQandA(column1 number) ON COMMIT PRESERVE ROWS';

.....

    EXECUTE IMMEDIATE ' insert into TempQandA(column1) VALUES (1)';
    END;

And Finally, you should not be creating the GTT on run time.. To avoid such issues. The GTT is anyway going to local to every session.

EDIT: As Lalit says, GTT's DDL doesn't accept CREATE OR REPLACE

Answer 2

'CREATE OR REPLACE GLOBAL TEMPORARY TABLE TempQandA(column1 number) ON COMMIT PRESERVE ROWS';

The keyword REPLACE is incorrect. You need to simply create the GTT and insert the values into it using EXECUTE IMMEDIATE :

SQL> BEGIN
  2  EXECUTE IMMEDIATE 'CREATE GLOBAL TEMPORARY TABLE Temp_gtt(column1 number) ON COMMIT PRESERVE ROWS';
  3  EXECUTE IMMEDIATE 'insert into temp_gtt(column1) values(1)';
  4  END;
  5  /

PL/SQL procedure successfully completed.

SQL>
SQL> select * from temp_gtt;

   COLUMN1
----------
         1

SQL>