LNNVL

Syntax

Description of the illustration lnnvl.gif

Purpose

LNNVL provides a concise way to evaluate a condition when one or both operands of the condition may be null. The function can be used in the WHERE clause of a query, or as the WHEN condition in a searched CASE expression. It takes as an argument a condition and returns TRUE if the condition is FALSE or UNKNOWN and FALSE if the condition is TRUE. LNNVL can be used anywhere a scalar expression can appear, even in contexts where the IS [NOT] NULL, AND, or OR conditions are not valid but would otherwise be required to account for potential nulls.

Oracle Database sometimes uses the LNNVL function internally in this way to rewrite NOT IN conditions as NOT EXISTS conditions. In such cases, output from EXPLAIN PLAN shows this operation in the plan table output. The condition can evaluate any scalar values but cannot be a compound condition containing AND, OR, or BETWEEN.

The table that follows shows what LNNVL returns given that a = 2 and b is null.

Condition	Truth of Condition	LNNVL Return Value
a = 1	`FALSE`	`TRUE`
a = 2	`TRUE`	`FALSE`
a `IS` `NULL`	`FALSE`	`TRUE`
b = 1	`UNKNOWN`	`TRUE`
b `IS` `NULL`	`TRUE`	`FALSE`
a = b	`UNKNOWN`	`TRUE`

Examples

Suppose that you want to know the number of employees with commission rates of less than 20%, including employees who do not receive commissions. The following query returns only employees who actually receive a commission of less than 20%:

SELECT COUNT(*)
  FROM employees
  WHERE commission_pct < .2;

  COUNT(*)
----------
        11

To include the 72 employees who receive no commission at all, you could rewrite the query using the LNNVL function as follows:

SELECT COUNT(*)
  FROM employees
  WHERE LNNVL(commission_pct >= .2);

  COUNT(*)
----------
        83