Execute select/insert statement within an IF clause Oracle - oracle

Question

I need to execute some statements within the IF clause only if a table exists.
But the issue I am facing is, even when the condition is false, the statements are getting executed.
DECLARE
count_matching_row NUMBER := 0;
count_matching_tbl NUMBER := 0;
BEGIN
SELECT COUNT(*)
INTO count_matching_tbl
FROM user_tables
WHERE LOWER(table_name) = 'tab1';
IF(count_matching_tbl = 1)
THEN
SELECT COUNT (*)
INTO count_matching_row
FROM test1
WHERE ID IN (SELECT ID FROM tab1);
IF(count_matching_row = 0)
THEN
INSERT INTO review_case
SELECT
DISTINCT ID, d,e
FROM tab1
WHERE ID IS NOT NULL;
INSERT INTO review_case_payer
SELECT
a,b,c
FROM tab1
WHERE a IS NOT NULL;
COMMIT;
END IF;
END IF;
END;
/
Whenever I execute these statements, if the table 'tab1' exists it works fine.
If the table tab1 does not exist I get the error
"ORA-06550: line 13, column 14:
PL/SQL: ORA-00942: table or view does not exist"
I get similar errors for each line where I try to access table "tab1"
I tried with ref cursor but still the same, I cannot use it for insert statements.

Answer 1

Your error is due to the fact that you're using a table that may not exist; this error is thrown because the script has compile problems, not data problems, so the way you try to use the IF is not enough to handle your situation.
You need to use some dynamic SQL to handle an object that could not exist; for example, see the following.
If the table does not exist, nothing will be done:
SQL> select * from tab1;
select * from tab1
*
ERROR at line 1:
ORA-00942: table or view does not exist
SQL> declare
2 vCountTab number;
3 begin
4 select count(1)
5 into vCountTab
6 from user_tables
7 where table_name = 'TAB1';
8
9 if vCountTab = 1 then
10 execute immediate 'insert into TAB1 values (1, 2)';
11 end if;
12 end;
13 /
PL/SQL procedure successfully completed.
If the table exists, the insert will be done:
SQL> create table tab1(a number, b number);
Table created.
SQL> declare
2 vCountTab number;
3 begin
4 select count(1)
5 into vCountTab
6 from user_tables
7 where table_name = 'TAB1';
8
9 if vCountTab = 1 then
10 execute immediate 'insert into TAB1 values (1, 2)';
11 end if;
12 end;
13 /
PL/SQL procedure successfully completed.
SQL> select * from tab1;
A B
---------- ----------
1 2
SQL>