Which of the following KEYWORDS will return the first NON-NULL value from a list of columns?
Explanation
COALESCE function evaluates the arguments one by one and returns the value of the first expression that does not evaluate to NULL.
Theory
• #### General Functions

The objective of the general NULL handling functions is to replace the NULL values with an alternate value.
• NVL - The NVL function substitutes an alternate value for a NULL value.
• NVL2 - As an enhancement over NVL, Oracle introduced a function to substitute value not only for NULL columns values but also for NOT NULL columns.
• NULLIF - The NULLIF function compares two arguments expr1 and expr2. If expr1 and expr2 are equal, it returns NULL; else, it returns expr1. First argument can't be NULL.
• COALESCE - COALESCE function, a more generic form of NVL, returns the first non-null expression in the argument list.

• #### COALESCE

COALESCE function, a more generic form of NVL, returns the first non-null expression in the argument list. It takes minimum two mandatory parameters but maximum arguments has no limit.

#### Syntax

``````COALESCE (expr1, expr2, ... expr_n )
``````
Consider the below SELECT query. It selects the first not null value fed into address fields for an employee.
``````SELECT COALESCE (address1, address2, address3) Address
FROM  employees;
``````
The working of COALESCE function is similar to IF..ELSIF..ENDIF construct. The query above can be re-written as:
``````IF address1 is not null THEN
ELSIF address2 is not null THEN
ELSIF address3 is not null THEN