How to achieve default value if column value is NULL? - mysql

Question

I want to retrieve some column values from table with these conditions.
If value is NULL (or) Empty String , return some user defined value
If not above condition , return it's value.
How can I figure it out ?
Here is my Table query..
CREATE TABLE AUCTION_CAR_BID(
bid_seq bigint NOT NULL AUTO_INCREMENT,
auction_car_seq bigint NOT NULL,
bid_group_seq bigint NOT NULL,
bid_price int DEFAULT 0 NOT NULL,
over_bid_price int DEFAULT -1 NOT NULL,
result_id int DEFAULT 0 NOT NULL,
remark varchar(500),
PRIMARY KEY (bid_seq))
ENGINE = InnoDB DEFAULT CHARACTER SET utf8;
Here is my efforted codes to get it..
SELECT
COALESCE(OVER_BID_PRICE, -1)
FROM
AUCTION_CAR_BID
WHERE
BID_SEQ = 2354435345;
Another :
SELECT
CASE
WHEN OVER_BID_PRICE IS NULL
OR TRIM(OVER_BID_PRICE) = '' THEN -1
ELSE OVER_BID_PRICE
END OVER_BID_PRICE
FROM
AUCTION_CAR_BID
WHERE
BID_SEQ = 2354435345;
But I always get empty String value(not -1) if given id is not in my table.
Any suggestions would be really appreciated !

Answer 1

If you write this:
SELECT
COALESCE(OVER_BID_PRICE, -1)
FROM
AUCTION_CAR_BID
WHERE
BID_SEQ = 2354435345;
The results can be two types.
First result: Your query no returns rows! Your WHERE condition is unsatisfact so you'll read NULL
Second result: Your query returns rows but the value of your field is NULL, your COALESCE works fine in this case
To resolve you can try this:
SELECT COALESCE(
(SELECT
COALESCE(OVER_BID_PRICE, -1)
FROM AUCTION_CAR_BID
WHERE BID_SEQ = 2354435345)
,-1);
Tell me if it's OK

Answer 2

How about this:
select
case when price is null or id <> 1
then -1
else price
end price
from mytable

Answer 3

DROP TABLE prices;
CREATE TABLE prices (price_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,price INT NULL);
INSERT INTO prices (price) VALUES (' '),(''),(NULL);
SELECT * FROM prices;
+----------+-------+
| price_id | price |
+----------+-------+
| 1 | 0 |
| 2 | 0 |
| 3 | NULL |
+----------+-------+
SELECT price_id,COALESCE(price,-1) price FROM prices;
+----------+-------+
| price_id | price |
+----------+-------+
| 1 | 0 |
| 2 | 0 |
| 3 | -1 |
+----------+-------+

Answer 4

If there's no row for USER_SEQ = 2354435345 in your table there's no row returned. But aggregate functions always return a row even if the result is empty :-)
SELECT
COALESCE(MIN(OVER_BID_PRICE), -1)
FROM
USER_PARAM
WHERE
USER_SEQ = 2354435345;