PREVIOUS

Syntax

Description of the illustration previous.eps

Purpose

The PREVIOUS function can be used only in the model_clause of the SELECT statement and then only in the ITERATE ... [ UNTIL ] clause of the model_rules_clause. It returns the value of cell_reference at the beginning of each iteration.

See Also:

• model_clause and "Model Expressions" for the syntax and semantics

• Appendix C in Oracle Database Globalization Support Guide for the collation derivation rules, which define the collation assigned to the return value of PREVIOUS when it is a character value

Examples

The following example repeats the rules, up to 1000 times, until the difference between the values of cur_val at the beginning and at the end of an iteration is less than one:

SELECT dim_col, cur_val, num_of_iterations
  FROM (SELECT 1 AS dim_col, 10 AS cur_val FROM dual)
  MODEL
    DIMENSION BY (dim_col)
    MEASURES (cur_val, 0 num_of_iterations)
    IGNORE NAV
    UNIQUE DIMENSION
    RULES ITERATE (1000) UNTIL (PREVIOUS(cur_val[1]) - cur_val[1] < 1)
    (
      cur_val[1] = cur_val[1]/2,
      num_of_iterations[1] = num_of_iterations[1] + 1
    );

   DIM_COL    CUR_VAL NUM_OF_ITERATIONS
---------- ---------- -----------------
         1       .625                 4