plsql: execute query: invalid identifier - dynamic

Question

Why can't I execute the stmt query?
It shows tabb is invalid identifier.
TYPE tab_row IS TABLE OF tab_name%ROWTYPE;
tabb tab_row;
TYPE cur_ref Is Ref Cursor;
c cur_ref;
stmt_string Varchar2(1000);
stmt Varchar2(1000);
Begin
stmt_string := 'Select * from ' || tab1 || ' mft
Where mft.mfmt_id IS NOT NULL
and mft.MFMT_FLAG IS NULL';
Open c For stmt_string;
Fetch c bulk collect into tabb;
Close c;
stmt:= 'Update '|| tab || ' m
Set m.mfmt_mat_bnr = tabb(i).mfmt_mat_bnr,
m.mfmt_mat_type = tabb(i).mfmt_mat_type,
m.mfmt_be_seg = tabb(i).mfmt_be_seg
Where m.mfmt_id = tabb(i).mfmt_id';
For i in 1..tabb.count loop
Execute Immediate stmt;
End loop;
End;

Answer 1

I have not seen where is tabb being declared. As you mentioned in your comment, it is a collection.
From your code I can understand you are looping through the values of this collection. This means these values are variables i.e. changing values every iteration. Therefore, you need to use them as such.
You current dynamic statement, this values are static string. This Set m.mfmt_mat_bnr = tabb(i).mfmt_mat_bnr, will result in the same string every iteration. Hence, you need to change that to Set m.mfmt_mat_bnr = '|| tabb(i).mfmt_mat_bnr||', ...etc
I can rewrite your code as follows:
TYPE tab_row IS TABLE OF tab_name%ROWTYPE;
tabb tab_row;
TYPE cur_ref Is Ref Cursor;
c cur_ref;
stmt_string Varchar2(1000);
stmt Varchar2(1000);
Begin
stmt_string := 'Select * from ' || tab1 || ' mft
Where mft.mfmt_id IS NOT NULL
and mft.MFMT_FLAG IS NULL';
Open c For stmt_string;
Fetch c bulk collect into tabb;
Close c;
stmt:= 'Update '|| tab || ' m
Set m.mfmt_mat_bnr = '||tabb(i).mfmt_mat_bnr||',
m.mfmt_mat_type = '||tabb(i).mfmt_mat_type||',
m.mfmt_be_seg = '||tabb(i).mfmt_be_seg||'
Where m.mfmt_id = '||tabb(i).mfmt_id;
For i in 1..tabb.count loop
Execute Immediate stmt;
End loop;
End;
Since this code is not tested, one thing I strongly recommend to confirm first. Is that tabb is correctly declared within the scope.

Answer 2

If the problem is in your loop where you execute your statement, maybe try using EXECUTE IMMEDIATE .. USING statement?
The syntax is:
EXECUTE IMMEDIATE <SQL Command>
[INTO <variable list>]
[USING <bind variable list>];
You might try the code below, then:
DECLARE
-- your tab1 may contain some insignificant columns with values (especially huge ones e.g. CLOB/BLOB)
-- which will extremely affect procedure's efficiency, so it's a better practice to select only those values that we need
TYPE t_tab_rec IS RECORD (
mfmt_mat_bnr tab_name.mfmt_mat_bnr%TYPE
,mfmt_mat_type tab_name.mfmt_mat_type%TYPE
,mfmt_be_seg tab_name.mfmt_be_seg%TYPE
,mfmt_id tab_name.mfmt_id%TYPE
);
TYPE t_tab_arr IS TABLE OF t_tab_rec;
tabb t_tab_arr := NEW t_tab_arr();
TYPE ref_cur IS REF CURSOR RETURN t_tab_rec; -- to assure cursor is returning t_tab_rec type records
c cur_ref;
stmt_select VARCHAR2(1000);
stmt_upadte VARCHAR2(1000);
BEGIN
stmt_select :=
'SELECT
mft.mfmt_mat_bnr
,mft.mfmt_mat_type
,mft.mfmt_be_seg
,mft.mfmt_id
FROM
'||tab1||' mft
WHERE
mft.mfmt_id IS NOT NULL
AND mft.mfmt_flag IS NOT NULL';
OPEN c FOR stmt_select;
FETCH c BULK COLLECT INTO tabb;
CLOSE c;
stmt_upadte :=
'UPDATE '||tab||'
SET mfmt_mat_bnr = :p_mfmt_mat_bnr
,mfmt_mat_type = :p_mfmt_mat_type
,mfmt_be_seg = :p_mfmt_be_seg
WHERE
mfmt_id = :p_mfmt_id';
FOR idx IN tabb.FIRST .. tabb.LAST
LOOP
EXECUTE IMMEDIATE stmt_update USING tabb(idx).mfmt_mat_bnr, tabb(idx).mfmt_mat_type, tabb(idx).mfmt_be_seg, tabb(idx).mfmt_id;
END LOOP;
END;
/