This section applies only to symbols that appear in the Pattern argument, described in Arguments. For information about symbols that appear in the Result argument, refer to Results.
For each symbol definition, col_expr = symbol_predicate AS symbol, the function returns the rows for which col_expr equals symbol_predicate. For example, for pagetype = 'home' AS H, the function returns the first and fourth rows of the following table.
| sessionid | clicktime | userid | productname | pagetype | referrer | productprice |
|---|---|---|---|---|---|---|
| 1 | 07:00:10 | 333 | home | www.company2.com | ||
| 1 | 07:00:12 | 333 | product1 | checkout | www.company2.com | 200.2 |
| 1 | 07:01:00 | 333 | product2 | checkout | 340 | |
| 13 | 15:35:08 | 67403 | home | www.company1.com |
The function does not return any row that contains a NULL value. For example, for pagetype = 'checkout' AS C, the function returns the second row of the preceding table, but not the third.
The predicate TRUE matches every row.
If symbols have overlapping predicates, multiple symbols might match the same row.