I would like to write the a query in mySQL that has the following form:
SELECT *,
CASE
WHEN <column name> = 1 THEN 1
ELSE 0
END as "column_1",
CASE
WHEN <column name> = 2 THEN 1
ELSE 0
END as "column_2",
CASE
WHEN <column name> = 3 THEN 1
ELSE 0
END as "column_3"
FROM <table name>;
I would like to write this query for a large number of cases (approximately 1000 cases), such that 1000 new columns are created that satisfy the conditions given above. How can I iterate this process in mySQL so that I don't have to write each line manually as I have done above (where there are only 3 cases)?
This may not be appropriate, but if you can live with one column of output (as a string rather than as multiple columns), then you might be able to do the following:
select t.id,
group_concat( (case when t.column = v.value then '1' else '0' end) order by v.ordering) as string_flags
from (select 1 as ordering, 1 as value union all
select 2, 2 union all
. . .
) v cross join
t
group by t.id;
This is just an idea. Performance is an issue, but it also gets around issues with the maximum number of columns in a row.
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