NULL Value
NULL is a reserved keyword used to indicate that a data value is unknown. It is the ASCII abbreviation for NULL characters (\0).
Usage in Expressions
Vertica does not treat an empty string as a NULL value. An expression must specify NULL to indicate that a column value is unknown.
The following considerations apply to using NULL in expressions:
- NULL is not greater than, less than, equal to, or not equal to any other expression. Use the Boolean predicate to determine whether an expression value is NULL.
- You can write queries with expressions that contain the
<=>operator forNULL=NULLjoins. See Equi-Joins and Non Equi-Joins in Analyzing Data. - Vertica accepts NULL characters (
'\0') in constant strings and does not remove null characters from VARCHAR fields on input or output.
Projection Ordering of NULL Data
Vertica sorts NULL values in projection columns as follows:
| Column data type | NULL values placed at... |
|---|---|
| NUMERIC
INTEGER DATE TIME TIMESTAMP INTERVAL |
Beginning of sorted column (NULLS FIRST) |
| FLOAT
STRING BOOLEAN |
End of sorted column (NULLS LAST) |