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THIS Function
The THIS function is a sequence function that is used in the ROWS SINCE function to distinguish
between the value of the column in the current row and the value of the column in previous
rows (in an intermediate result table ordered by a SEQUENCE BY clause in a SELECT statement).
See
"ROWS SINCE Function" (page
THIS is a Neoview SQL extension.
THIS (column-expression)
column-expression
specifies a derived column determined by the evaluation of the column expression. If the
value of the expression is null, THIS returns null.
Considerations for THIS
Counting the Rows
You can use the THIS function only within the ROWS SINCE function. For each row, the ROWS
SINCE condition is evaluated in two steps:
1.
The expression for THIS is evaluated for the current row. This value becomes a constant.
2.
The condition is evaluated for the result table, using a combination of the THIS constant
and the data for each row in the result table, starting with the previous row as row 1 (up to
the maximum number of rows or the size of the result table).
If a row is reached where the condition is true, ROWS SINCE returns the number of rows counted
so far. Otherwise, if the condition is never true within the result table being considered, ROWS
SINCE returns null. Neoview SQL then goes to the next row as the new current row and the
THIS constant is reevaluated.
Example of THIS
•
Return the number of rows since the condition I1 less than a previous row became true:
SELECT ROWS SINCE (THIS(I1) < I1) AS ROWS_SINCE_THIS
FROM mining.seqfcn
SEQUENCE BY TS;
ROWS_SINCE_THIS
---------------
--- 5 row(s) selected.
476
SQL Functions and Expressions
451).
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