MySQL CASE to update multiple columns - mysql

Question

I would like to update multiple columns in my table using a case statement, but I cannot find how to do this (is this even possible). I came up with the following invalid reference query:
UPDATE tablename SET
CASE name
WHEN 'name1' THEN col1=5,col2=''
WHEN 'name2' THEN col1=3,col2='whatever'
ELSE col1=0,col2=''
END;
Is there any way of achieving the expected result with valid SQL?

Answer 1

UPDATE tablename
SET col1 = CASE WHEN name = 'name1' THEN 5
WHEN name = 'name2' THEN 3
ELSE 0
END
, col2 = CASE WHEN name = 'name1' THEN ''
WHEN name = 'name2' THEN 'whatever'
ELSE ''
END
;

Answer 2

I don't know of any clean way to do what you're asking. An equivalent valid SQL update would be:
UPDATE tablename SET
col1 = CASE name WHEN 'name1' THEN 5 WHEN 'name2' THEN 3 ELSE 0 END,
col2 = CASE name WHEN 'name1' THEN '' WHEN 'name2' THEN 'whatever' ELSE '' END;
Of course this isn't pretty and requires repeating the same cases (e.g. 'name1') multiple times, but I just don't think it's possible any other way.

Answer 3

If name has a unique index and your values are known to exist in the table, you can use this trick:
INSERT INTO tablename (name, col1, col2)
VALUES ('name1', 5, '')
, ('name2', 3, 'whatever')
ON DUPLICATE KEY UPDATE
col1 = VALUES(col1)
, col2 = VALUES(col2);
If there are any additional NOT NULL columns without a default value, you'll have to add dummy values for those. Just leave them out of the ON DUPLICATE KEY UPDATE and they'll be ignored.

Answer 4

You have two options that are covered in the different answers of this question:
UPDATE ... CASE
INSERT INTO ... ON DUPLICATE KEY
I had the following requirement:
bulk update 100000+ records with 4 column values
the source might have records that do not trigger the "ON DUPLICATE KEY" thus just inserting new data instead of just updating. At the same time I do not want these new records.
So there are two bad alternatives:
using UPDATE ... CASE for multiple columns makes this really expensive for the database when updating 100000+ records
using INSERT INTO ... ON DUPLICATE KEY might insert records that I do not want
My solution: Use INSERT INTO ... ON DUPLICATE KEY with dummy data, then delete all records that include column with the UNWANTED_INSERTED_DATA flag
I am inserting one column with UNWANTED_INSERTED_DATA as a flag where I can guarantee these values will never be part of any real data. The remaining columns are updated with the wanted data.
INSERT INTO tablename (name, col1, col2)
VALUES ('name1', 5, 'UNWANTED_INSERTED_DATA')
, ('name2', 3, 'UNWANTED_INSERTED_DATA')
ON DUPLICATE KEY UPDATE
name = VALUES(name)
, col1 = VALUES(col1)
; # DO NOT include the UNWANTED_INSERTED_DATA in the update part
The records I want only use update thus never receive the dummy data with UNWANTED_INSERTED_DATA column.
The records I do not want contain the dummy data.
I can then delete all unwanted inserted records with dummy data in one delete query:
DELETE FROM tablename WHERE col2 = 'UNWANTED_INSERTED_DATA'
This is a hacky solution but gets the job done with just two queries in two steps.