CODEWITHSUNDEEP
mysqlsqlunpivot
pluck
pluck

Reputation: 97

need help writing a query (restructuring the table)

I need to write a select statement that will rewrite the table in the following manner... I'm not sure how to go about this using MySQL.

Example of table

user_id   date         a    b    c     
123456    2020-01-01   1    1    1
234567    2020-03-04   1    0    0
453576    2020-05-05   1    0    1

Desired result

user_id   date        results
123456    2020-01-01  a
123456    2020-01-01  b
123456    2020-01-01  c
234567    2020-03-04  a
453576    2020-05-05  a
453576    2020-05-05  c

Upvotes: 1

Views: 41

Answers (2)

Gordon Linoff
Gordon Linoff

Reputation: 1270463

If you have a large amount of data or your "table" is really a complex query (say a subquery or view), then unpivoting is usually faster with cross join than with union all:

select t.user_id, t.date, r.result
from t cross join
     (select 'a' as result union all
      select 'b' as result union all
      select 'c' as result 
     ) r
where (t.a = 1 and r.result = 'a') or
      (t.b = 1 and r.result = 'b') or
      (t.c = 1 and r.result = 'c') ;

For a single smallish table, performance probably doesn't matter.

Upvotes: 1

GMB
GMB

Reputation: 222582

In MySQL you can unpivot with union all, while filtering on 1 values:

select user_id, date, 'a' as result from mytable where a = 1
union all select user_id, date, 'b' from mytable where b = 1
union all select user_id, date, 'c' from mytable where c = 1
order by user_id, date, result

Upvotes: 3

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