MYSQL CASE THEN statement with multiple values

Question

I am trying go select multiple values with CASE statement. I noticed we cannot do

CASE 
    WHEN wall.type=\"bk\" 
    THEN books.id1,books.id2, //         


        

Answer 1

And everything can be done, but it always depends on what you want to do. Below I'll show you a working example right after you have to take the data as an array and do what you want.

CREATE TABLE wall (`ident` int,`type` varchar(2), `order` int);
INSERT INTO wall (`ident`, `type`, `order`) VALUES
    (40,'bk', 1),
    (41,'bk', 5),
    (42,'rt', 2),
    (43,'bk', 3),
    (44,'rt', 1);

CREATE TABLE books (`ident` int,`id1` int, `time` varchar(8), `id2` int);
INSERT INTO books (`ident`, `id1`, `time`, `id2`) VALUES
    (40, 10, '18:07:00', 20),
    (43, 11, '05:00:00', 21),
    (44, 12, '21:01:00', 22),
    (41, 13, '10:00:00', 23),
    (42, 14, '23:10:00', 24);
#--------------------------
SELECT 
  CASE 
    WHEN wall.type='bk' 
    THEN  CONCAT(books.id1,'-',books.id2) 
 END AS column_1

FROM wall JOIN books ON books.ident = wall.ident GROUP BY wall.ident ORDER BY wall.ident ASC;

Print:

 column_1
1   10-20
2   13-23
3   NULL
4   11-21
5   NULL

Solution in action via this link: http://rextester.com/LHPI38373

Answer 2

No. CASE statement can only return a single value, so the only way to achieve what you want is duplicate the case ...

The database server should be optimized and perform only one time the check on the same condition ...

Answer 3

No, it is just a single value. Additionally, it is contradictory to use "multiple columns" and name those multiple columns as column_1, right? :)

You can use another column to store the other id with (a similar case) and use nulls to represent the else values, just like you're doing now.

Example:

CASE 
    WHEN wall.type="bk" 
    THEN books.id1
END as column_1,
CASE 
    WHEN wall.type="bk" 
    THEN books.id2
END as column_2

Check the official documentation for more information.

Answer 4

According to documentation mysql_doc; you can use you can use the other syntax of case for what you wanted.

case
 WHEN FIND_IN_SET(edu, "1,1st,2,2nd,3,3rd,4,4th,5,5th,pri,primary,primery") THEN
  SET memEdu = "Primary";
 WHEN FIND_IN_SET(edu, "intermediate,inter,f.a,fa,fac,f.a.c,f.sc,fsc,1rd year,2rd year,3rd year") THEN
  SET memEdu = "Intermediate";
End case;