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Creating multiple rows from a group of columns

A master record stores the rolling balances for the next thirty days. I need to store these rolling balances as individual records in a detail table. How can I achieve this in PL/SQL, i.e. one record of the master table gets converted to 30 records in detail table?

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I suppose it might be possible to do this with PL/SQL code such as

BEGIN 
  X := 1; 
  WHILE (X < 31) 
  LOOP 
    insert into detail (nextday, balance)
       select X, ??(X) from master;
    X := X + 1; 
  END LOOP; 
END;

... assuming you have some way (denoted by "??" above) of accessing the 30 fields as though they were elements of an array. I think you can do this in SQL-99 but it would require that the table was defined that way, and that your database supports the array structure. More likely is that the table has discretely named columns, such as balance1, balance2, ... balance30.

The obvious solution is simply to code 30 INSERT statements instead of a loop --

insert into detail (nextday, balance)
    select 1, balance1 from master;
insert into detail (nextday, balance)
    select 2, balance2 from master;
 ...
insert into detail (nextday, balance)
    select 30, balance30 from master;

With cut and paste in text editors, this is probably the easiest way to go.

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This was first published in March 2002

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