The COALESCE function returns the first non-null expression in a parameter list. You must specify at least two parameters.
Syntax
COALESCE(expr1, expr2[,..., exprn])
Parameters
Parameter |
Description |
|---|---|
| expr1, expr2[,..., exprn] | The non-null expressions. You must specify at least two non-null expressions. |
Return type
The first non-null expression in the parameter list is returned. If all the parameters are NULL, NULL is returned.
Examples
Assume that a product_information table is available. In the table, product_id indicates a product ID, list_price indicates the original price of the product, min_price indicates the lowest price of the product, and Sale indicates the actual sale price of the product. Specify the product discount as 10% and calculate the actual sale price of each product. In this case, you can use the COALESCE function. If list_price is empty, perform calculations based on min_price . If min_price is also empty, perform calculations based on 5 .
You can execute the following statements to create the product_information data table and insert data into the table:
CREATE TABLE product_information(supplier_id INT, product_id INT,list_price numeric, min_price numeric);
INSERT INTO PRODUCT_INFORMATION VALUES ('102050', '1659', '45', NULL);
INSERT INTO PRODUCT_INFORMATION VALUES ('102050', '1770', NULL, '70');
INSERT INTO PRODUCT_INFORMATION VALUES ('102050', '2370', '305', '247');
INSERT INTO PRODUCT_INFORMATION VALUES ('102050', '2380', '750', '731');
INSERT INTO PRODUCT_INFORMATION VALUES ('102050', '3255', NULL, NULL);
Execute the following query statement:
SELECT product_id, list_price,min_price,COALESCE(0.9*list_price, min_price, 5) "Sale"
FROM product_information WHERE supplier_id = 102050 ORDER BY product_id;
The following query result is returned:
+--------------+--------------+------------+--------+
| PRODUCT_ID | LIST_PRICE | MIN_PRICE | Sale |
+--------------+--------------+------------+--------+
| 1659 | 45 | | 40.5 |
+--------------+--------------+------------+--------+
| 1770 | | 70 | 70 |
+--------------+--------------+------------+--------+
| 2370 | 305 | 247 | 274.5 |
+--------------+--------------+------------+--------+
| 2380 | 750 | 731 | 675 |
+--------------+--------------+------------+--------+
| 3255 | | | 5 |
+--------------+--------------+------------+--------+