Having prob in retrieving data

Question

Basically i have 2 tables ...
__TABLE 1:__
COL_NAME COL_VALUE
Name Col_3
Rno Col_2
Class Col_1
__TABLE 2:__
COL_1 COL_2 COL_3
Sharath 111 mca
Sandeep 102 btech
Amar 103 mba
BOTH THE TABLES ARE LINKED.TABLE2 COLUMN NAMES ARE VALUES IN TABLE 1
Now My prob is i want a query that gets COL_VALUE from TABLE1 based on given COL_NAME and get the data from TABLE2 of that value got from TABLE1.

Answer 1

# You need to play really dynamically in building your SQL's if storing metadata inside table. Also this may create problem if metadata is not handled properly
# Below is simple demonostration where you pass your first table col name and we derive the col value for second table and execute SQL to get data from second table
SQL>CREATE TABLE T1
  2  (
  3    COL_NAME  VARCHAR2(10),
  4    COL_VALUE VARCHAR2(10)
  5  );
Table created.
SQL>
SQL>INSERT INTO T1 VALUES ('NAME', 'COL_1');
1 row created.
SQL>INSERT INTO T1 VALUES ('RNO', 'COL_2');
1 row created.
SQL>INSERT INTO T1 VALUES ('CLASS', 'COL_3');
1 row created.
SQL>
SQL>CREATE TABLE T2
  2  (
  3    COL_1  VARCHAR2(10),
  4    COL_2  NUMBER,
  5    COL_3  VARCHAR2(10)
  6  );
Table created.
SQL>
SQL>INSERT INTO T2 VALUES ('Sharath', 111,'mca');
1 row created.
SQL>INSERT INTO T2 VALUES ('Sandeep', 102,'btech');
1 row created.
SQL>INSERT INTO T2 VALUES ('Amar', 103,'mba');
1 row created.
SQL>
SQL>CREATE OR REPLACE PROCEDURE GET_T2_SQL(P_COL_NAME T1.COL_NAME%TYPE, P_RC OUT SYS_REFCURSOR) IS
  2   V_SQL VARCHAR2(32767) := NULL;
  3  BEGIN
  4
  5  SELECT 'SELECT ' || COL_VALUE || ' FROM T2'
  6  INTO V_SQL
  7  FROM  T1
  8  WHERE T1.COL_NAME = P_COL_NAME;
  9
10  OPEN P_RC FOR V_SQL;
11
12  EXCEPTION
13    WHEN NO_DATA_FOUND THEN
14      RAISE_APPLICATION_ERROR(-20001, P_COL_NAME || ' not found in table -T1.COL_NAME');
15  END;
16  /
Procedure created.
SQL>variable RC REFCURSOR;
SQL>EXEC GET_T2_SQL('NAME',:RC);
PL/SQL procedure successfully completed.
SQL>PRINT RC;
COL_1
Sharath
Sandeep
Amar
SQL>EXEC GET_T2_SQL('RNO',:RC);
PL/SQL procedure successfully completed.
SQL>PRINT RC;
     COL_2
       111
       102
       103
SQL>EXEC GET_T2_SQL('CLASS',:RC);
PL/SQL procedure successfully completed.
SQL>PRINT RC;
COL_3
mca
btech
mba
SQL>
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