COALESCE Function in DB2

In IBM's DB2, the COALESCE function is used to return the first non-null expression among its arguments. It evaluates a list of expressions and returns the first non-null value.

Here's the syntax:

COALESCE(expression1, expression2, ..., expression_n)

- expression1, expression2, ..., expression_n: These are the expressions that COALESCE evaluates. It can have multiple expressions separated by commas.

Example usage:

SELECT COALESCE(NULL, 'a', 'b', NULL, 'c'); -- Output: 'a'

SELECT COALESCE(NULL, NULL, NULL); -- Output: NULL

In the first example, COALESCE returns the first non-null value, which is 'a'. In the second example, all arguments are null, so COALESCE returns null.

Here are a few frequently asked questions about the COALESCE function in DB2:

1. What is the purpose of the COALESCE function in DB2?

   - The COALESCE function in DB2 returns the first non-null value among its arguments. It's commonly used to handle null values in queries.

2. How do I use COALESCE in a DB2 query?

   - You can use COALESCE in a DB2 query by providing the expressions you want to evaluate. For example:

     

     SELECT COALESCE(column1, column2, 'Default') AS Result FROM tableName;

     

     This query will return the first non-null value among column1, column2, and the string 'Default'.

3. Can COALESCE handle more than two expressions in DB2?

   - Yes, COALESCE can handle multiple expressions in DB2. You can provide as many expressions as needed.

4. Is COALESCE ANSI SQL-compliant in DB2?

   - Yes, COALESCE is ANSI SQL-compliant, and its usage is consistent with other relational database systems.

5. When should I use COALESCE instead of NVL in DB2?

   - Both COALESCE and NVL serve a similar purpose of handling null values, but COALESCE is more versatile as it can handle multiple expressions. NVL is specific to Oracle and only handles two expressions. If you need to handle more than two expressions or want ANSI compatibility, COALESCE is preferred.