SQL 合并两行ID相同但列值不同的行

Question

I am trying to merge different rows into one when they have the same id but different column values.

    (table1)

    id       colour

    1        red
    1        blue
    2        green
    2        red

I would like this to be combine so that the result is:

    id     colour1    colour2

    1      red        blue
    2      green      red

There is no limit for number of colors. It can range depending on the id.

Any help would be appreciated. Thanks in advance.

Answer 1

This would work for your specific example

select left(colours,locate(',',colours)-1) as colour1, right(colours, length(colours)- locate(',',colours)) as colour2 from (select id, group_concat(colour) as colours from table1 group by id) concatenation

not very general or robust.

If the set of values (colours) were fixed, I'd prefer to pivot it like this:

select id, sum(RED) as RED, sum(GREEN) as GREEN, sum(BLUE) as BLUE from (select id, colour='red' as RED, colour='green' as GREEN, colour='blue' as BLUE from table1) coded group by id;

but that wasn't the output format you requested.