A symbol identifies a row in the Pattern and Result syntax elements. A symbol can be any valid identifier (that is, a sequence of characters and digits that begins with a character) but is typically one or two uppercase letters. Symbols are case-insensitive; that is, 'SU' is identical to 'su', and the system reports an error if you use both.
For example, suppose that you have this input table:
| record | city | temp | rh | cloudcover | windspeed | winddirection | rained_next_day |
|---|---|---|---|---|---|---|---|
| 1 | ? | 81 | 30 | 0.0 | 5 | NW | 1 |
| 2 | Tempe | 76 | 40 | 0.2 | 15 | NE | 0 |
| 3 | ? | 70 | 70 | 0.4 | 10 | N | 0 |
| 4 | Tusayan | 75 | 50 | 0.4 | 5 | NW | 0 |
This table has examples of symbol definitions and the rows of the table that they match in NONOVERLAPPING mode:
| Symbol Definition | Rows Matched | ||||||
|---|---|---|---|---|---|---|---|
| temp >= 80 AS H | 1 | ||||||
| winddirection = 'NW' AS NW | 1, 4 | ||||||
| winddirection = 'NW' OR windspeed > 12 AS W | 1, 2, 4 | ||||||
| cloudcover <> 0.0 AND rh > 35 AS C | 2, 3, 4 | ||||||
| TRUE AS A | 1, 2, 3, 4 This symbol definition matches all rows, for any input table. |
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| city like 'tu%' AS TU | The like operator depends on Teradata Session mode:
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| city not like 'tu%' AS TU | 2 | ||||||
| city not like 'Tu%' AS N | 2 | ||||||
| city like 'Tu%n' as T | 1, 3, 4 The % operator matches any number of characters. |
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| city like 'Tu___n' as T | 1, 3 The underscore (_) operator matches any single character. The pattern 'Tu___n' has three underscores, so it matches 'Tucson' but not 'Tusayan'. |
Rows with NULL values do not match any symbol. That is, the function ignores rows with missing values.