Stored procedure as a column in a table

Question

Is it possible to have a column defined as a stored procedure in a table?
I was told that this could be done and that other columns on that row could be used in the stored procedure and you would query the data just as you would for any other column (i.e. select storProcColumn from table).
The reason I am asking is that the column that I want as a stored procedure needs to be calculated every time that column is asked for as it is a calculation from many pieces of data.
The plan is to make a Java stored procedure that will do the calculation, define a column that points to a Java stored procedure, which will do the calculation using data from the row it is in along with other data from other tables.
I am familiar with Java stored procedures but don't know if it is possible to have a column point to it.
Can someone please point me to some documentation?
Thanks,
Dennis

Answer 1

I don't think that you can do exactly what you are expecting, but close. However, without knowing all of your requirements, I don't know if there might be a better way. You will need to use some form of dynamic SQL and it can get complicated and you will need to use functions rather than procedures if you expect to use them in a select statement. I have provided a demonstration below, in which I have created a table with the names of stored functions in one column and the values of parameters to be passed to the functions in the other column. After creating a bunch of java (using examples from the documentation) and some pl/sql, I have ultimately been able to perform a select from your table as you have requested, using just one function. The resulting data contains row counts of tables from one function, where the table name came from the other column in the row and a character string from another function, where the other column is null. I have used if ... end if to allow for the different parameters. Hopefully all of this will either help show you how to do it or help you decide that this is not the way to go and you need to come up with a simpler design for your system.
scott@ORA92> -- tables and data for testing:
scott@ORA92> CREATE TABLE test_tab
  2    (col1      VARCHAR2(10),
  3       func_col VARCHAR2(10))
  4  /
Table created.
scott@ORA92> INSERT INTO test_tab (col1, func_col)
  2  VALUES ('dept', 'row_count')
  3  /
1 row created.
scott@ORA92> INSERT INTO test_tab (col1, func_col)
  2  VALUES ('emp', 'row_count')
  3  /
1 row created.
scott@ORA92> INSERT INTO test_tab (col1, func_col)
  2  VALUES (NULL, 'HelloWorld')
  3  /
1 row created.
scott@ORA92> SELECT * FROM test_tab
  2  /
COL1       FUNC_COL
dept       row_count
emp        row_count
           HelloWorld
scott@ORA92> SELECT COUNT (*) FROM dept
  2  /
  COUNT(*)
         4
scott@ORA92> SELECT COUNT (*) FROM emp
  2  /
  COUNT(*)
        14
scott@ORA92> --
scott@ORA92> --
scott@ORA92> -- java and functions to perform calculations
scott@ORA92> -- based on other columns in row and other tables:
scott@ORA92> --
scott@ORA92> -- to count rows in a table:
scott@ORA92> create or replace and compile java source named "RowCounter" as
  2  import java.sql.*;
  3  import java.io.*;
  4  import oracle.jdbc.*;
  5 
  6  public class RowCounter {
  7    public static int rowCount (String tabName) throws SQLException {
  8        Connection conn =
  9          DriverManager.getConnection("jdbc:default:connection:");
10        String sql = "SELECT COUNT(*) FROM " + tabName;
11        int rows = 0;
12        try {
13          Statement stmt = conn.createStatement();
14          ResultSet rset = stmt.executeQuery(sql);
15          while (rset.next()) {rows = rset.getInt(1);}
16          rset.close();
17          stmt.close();
18        } catch (SQLException e) {System.err.println(e.getMessage());}
19        return rows;
20    }
21  }
22  /
Java created.
scott@ORA92> CREATE OR REPLACE FUNCTION row_count (tab_name VARCHAR2) RETURN NUMBER
  2  AS LANGUAGE JAVA
  3  NAME 'RowCounter.rowCount(java.lang.String) return int';
  4  /
Function created.
scott@ORA92> --
scott@ORA92> -- to return specific string:
scott@ORA92> create or replace and compile java source named "Hello" as
  2  public class Hello
  3  {
  4       public static String world ()
  5       {
  6          return "Hello world";
  7       }
  8  }
  9  /
Java created.
scott@ORA92> create or replace function HELLOWORLD return VARCHAR2 as
  2  language java name 'Hello.world () return java.lang.String';
  3  /
Function created.
scott@ORA92> --
scott@ORA92> --
scott@ORA92> -- function to calculate and return result using column values
scott@ORA92> -- containing function and table names as parameters
scott@ORA92> -- for dynamic execution:
scott@ORA92> CREATE OR REPLACE FUNCTION get_value
  2    (p_func IN VARCHAR2,
  3       p_col  IN VARCHAR2)
  4    RETURN       VARCHAR2
  5  AS
  6    v_result   VARCHAR2(20);
  7  BEGIN
  8    IF p_col IS NULL THEN
  9        EXECUTE IMMEDIATE
10          'SELECT ' || p_func || '() FROM DUAL'
11          INTO v_result;
12    ELSE
13        EXECUTE IMMEDIATE
14          'SELECT ' || p_func || '(''' || p_col || ''') FROM DUAL'
15          INTO v_result;
16    END IF;
17    RETURN v_result;
18  END get_value;
19  /
Function created.
scott@ORA92> SHOW ERRORS
No errors.
scott@ORA92> --
scott@ORA92> --
scott@ORA92> -- select statement that selects rows from your table
scott@ORA92> -- and uses the get_value function to pass the column values
scott@ORA92> -- for dynamic execution and return the results:
scott@ORA92> COLUMN result FORMAT A20
scott@ORA92> SELECT col1, func_col, get_value (func_col, col1) AS result
  2  FROM   test_tab
  3  /
COL1       FUNC_COL   RESULT
dept       row_count  4
emp        row_count  14
           HelloWorld Hello world
scott@ORA92>