Q

Looking at each value in a VARRAY

I have a table containing a VARRAY of objects as shown below. But I don't know how to find which divisions have an employee called John working in them. How could I look each value of the VARRAY: if the first value is not John, look at the next and so on until I get the value desired, or it realizes that the value doesn't exist?

CREATE OR REPLACE TYPE	emp_obj
AS	OBJECT
(
	last_name       VARCHAR (50),
	first_name      VARCHAR (50),
	birth_dt        DATE
);
/

CREATE OR REPLACE TYPE	emp_va
AS	VARRAY (999)
OF	emp_obj;
/

CREATE TABLE	division
(
	division_id	NUMBER (9)	PRIMARY KEY,
	division_name	VARCHAR2 (100),
	emps		emp_va
);
I know how to get all the items in my VARRAY with a query like:
SELECT	e.first_name
FROM	division        d
      ,	TABLE (d.emps)  e
WHERE	d.division_name	= 'Sales';

You've already done the hard part, isolating one component of each entry in the VARRAY, and you've shown how to use it in a SELECT clause. You can use single elements from the VARRAY in the WHERE clause in exactly the same way:

SELECT DISTINCT
        d.division_name
FROM    division        d
      , TABLE (d.emps)  e
WHERE   e.first_name = 'John';
That's the cleanest, easiest to understand way to get the results you want. Like many SQL statements, it does what you want, but it doesn't do it how you want it to: it doesn't stop after finding the first match within a single division. The solution below does quit looking after it finds the first match, so it will usually run faster:
SELECT  division_name
FROM    division        d
WHERE   EXISTS 
          ( SELECT  'X'   -- Why 'X'?  See note below.
            FROM    TABLE (d.emps)
            WHERE   first_name = 'John'
          );
Why 'X'? You could SELECT anything in the subquery: a literal (like I did) a column, SYSDATE, USER or a list of any kind(s) of values. The only crucial thing is whether or not the subquery returns any rows. SELECTing a literal is faster than SELECTing a real column or SYSDATE, so that's what I did.

This problem does not really revolve around the VARRAY: you could use the same techniques on plain old regular vanilla-flavored relational tables:

-- The straightforward but slower solution
SELECT DISTINCT
        d.division_name
FROM    division d
  JOIN  emp      e USING (division_id)
WHERE   e.first_name = 'John';

-- The faster but more convoluted solution
SELECT  division_name
FROM    division d
WHERE   EXISTS
          ( SELECT  'X'
            FROM    emp
            WHERE   first_name = 'John'
              AND   division_id = d.division_id
          );

If you want run the examples, or to experiment with related questions, you might want to copy these statements to populate the tables.


-- After creating the division table, as shown on the main page,
-- the following INSERT statements can be used to populate it.

-- The 'Sales' division will have two employees named John.
INSERT INTO division
(
 division_id,
 division_name,
 emps
)
VALUES
(
 1,
 'Sales',
 emp_va ( emp_obj ('Adams', 'John',    '30-Oct-1735'),
          emp_obj ('Adams', 'Abigail', '11-Nov-1744'),
          emp_obj ('Brown', 'John',    ' 9-May-1800')
        )
);

-- The 'Administration' division will have no employees named John.
INSERT INTO division
(
 division_id,
 division_name,
 emps
)
VALUES
(
 2,
 'Administration',
 emp_va ( emp_obj ('Bingen', 'Hildegard', '17-Sep-1098'),
          emp_obj ('Bush',   'George W.', ' 6-Jul-1946')
        )
);

-- Now the SELECT statements (based on the division table, only)
-- on the main page will run.

CREATE TABLE emp
AS
SELECT  d.division_id
      , e.last_name
      , e.first_name
      , e.birth_dt
FROM    division       d
      , TABLE (d.emps) e;

-- Now the queries on the main page that use the emp table will work.

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  • This was first published in July 2003
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