mysql-update multiple columns in a single row with multiple where clauses - mysql

Question

I have a mysql table as follows:
name | serialno | key
---------------------
NULL | NULL | 10
luke | 1234 | 20
NULL | NULL | 30
NULL | NULL | 40
I have to update a row where the name and the serialno update for a valid key.
The update statements that I am running are as follows:
UPDATE test SET Name = 'pc', Serialno = '10', WHERE `Key` = '10' AND name is null
and
UPDATE test SET Name = CASE
WHEN NULL THEN 'pc'
END
SET Serialno = CASE
WHEN NULL THEN '10'
END
Where `key` = '20'
The following errors get displayed:
1.
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHERE Key = '10' AND name is null' at line 1:
2.
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SET Serial = CASE
WHEN NULL THEN '10'
END
Where `key`='20'' at line 4:
Please help.

Answer 1

UPDATE test SET Name = CASE Name
WHEN NULL THEN 'pc'
END,
SET Serialno = CASE Serialno
WHEN NULL THEN '10'
END
Where `key` = '20'
You have to specify condition of your CASE

Answer 2

I don't really know what is the context (can you explain the detail what you want and then I will help you with better result).
However, as the StanislavL's answer, the syntax was wrong. I corrected it as below:
UPDATE test SET Name = CASE Name
WHEN NULL THEN 'pc'
END,
Serialno = CASE Serialno
WHEN NULL THEN '10'
END
Where `key` = '20'

Answer 3

Please do like this
UPDATE test SET Name = 'pc', Serialno = '10' WHERE `Key` = '10' AND name is null

Answer 4

Reasons for Errors:
Error 1 was because you have a , comma before WHERE Key = '10' ....
Statement should be:
UPDATE test SET Name = 'pc', Serialno = '10' WHERE `Key` = '10' AND name is null
Error 2 was because you have not instructed which case value to check in when clause. Acceptable syntaxes are:
1. CASE column_name WHEN value THEN expr1 ELSE expr2 END
2. CASE WHEN column_name <condition> value THEN expr1 ELSE expr2 END
Statement should be:
UPDATE test
SET
Name = CASE WHEN name IS NULL THEN 'pc' else name end
, Serialno = CASE WHEN serialno IS NULL THEN '10' else serialno end
END
Where `key` = '10'
Example # SQL Fiddle
You can extend this to set values for columns based on different key values without using where clause.
Example:
UPDATE test
SET
Name = CASE WHEN `key`=10 and name IS NULL THEN 'pc' else name end
, Serialno = CASE WHEN `key`=10 and serialno IS NULL THEN '10' else serialno end
, Name = CASE WHEN `key`=30 and name IS NULL THEN 'key is 30' else name end
, Serialno = CASE WHEN `key`=30 and serialno IS NULL THEN '3' else serialno end
END
Refer to: MySQL: CASE - WHEN syntax