values.rst

Data Types

Table of contents

• NULL and MISSING Values
  • General NULL and MISSING Values Handling
  • Special NULL and MISSING Values Handling

NULL and MISSING Values

ODFE SQL has two ways to represent missing information. (1) The presence of the field with a NULL for its value. and (2) the absence of the filed.

Please note, when response is in table format, the MISSING value is translate to NULL value.

Here is an example, Nanette doesn't have email field and Dail has employer filed with NULL value:

od> SELECT firstname, employer, email FROM accounts;
fetched rows / total rows = 4/4
+-------------+------------+-----------------------+
| firstname   | employer   | email                 |
|-------------+------------+-----------------------|
| Amber       | Pyrami     | [email protected]  |
| Hattie      | Netagy     | [email protected] |
| Nanette     | Quility    | null                  |
| Dale        | null       | [email protected]   |
+-------------+------------+-----------------------+

General NULL and MISSING Values Handling

In general, if any operand evaluates to a MISSING value, the enclosing operator will return MISSING; if none of operands evaluates to a MISSING value but there is an operand evaluates to a NULL value, the enclosing operator will return NULL.

Here is an example:

od> SELECT firstname, employer LIKE 'Quility', email LIKE '%com' FROM accounts;
fetched rows / total rows = 4/4
+-------------+---------------------------+---------------------+
| firstname   | employer LIKE 'Quility'   | email LIKE '%com'   |
|-------------+---------------------------+---------------------|
| Amber       | False                     | True                |
| Hattie      | False                     | True                |
| Nanette     | True                      | null                |
| Dale        | null                      | True                |
+-------------+---------------------------+---------------------+

Special NULL and MISSING Values Handling

THe AND, OR and NOT have special logic to handling NULL and MISSING value.

The following table is the truth table for AND and OR.

A	B	A AND B	A OR B
TRUE	TRUE	TRUE	TRUE
TRUE	FALSE	FALSE	TRUE
TRUE	NULL	NULL	TRUE
TRUE	MISSING	MISSING	TRUE
FALSE	FALSE	FALSE	FALSE
FALSE	NULL	FALSE	NULL
FALSE	MISSING	FALSE	MISSING
NULL	NULL	NULL	NULL
NULL	MISSING	MISSING	NULL
MISSING	MISSING	MISSING	MISSING

The following table is the truth table for NOT.

A	NOT A
TRUE	FALSE
FALSE	TRUE
NULL	NULL
MISSING	MISSING