Sum over multiple count field - mysql

Question

I try to sum mutliple count fields with JOOQ and a MySQL database.
At the moment my code looks like this:
int userId = 1;
Field<Object> newField = DSL.select(DSL.count()).from(
DSL.select(DSL.count())
.from(REQUIREMENT)
.where(REQUIREMENT.CREATOR_ID.equal(userId))
.unionAll(DSL.select(DSL.count())
.from(REQUIREMENT)
.where(REQUIREMENT.LEAD_DEVELOPER_ID.equal(userId)))
which always returns 2 as newField. But I want know how many times an user is the creator of a requirement PLUS the lead developer of a requirement.

Answer 1

You say "sum over multiple count", but that's not what you're doing. You do "count the number of counts". The solution is, of course, something like this:
// Assuming this to avoid referencing DSL all the time:
import static org.jooq.impl.DSL.*;
select(sum(field(name("c"), Integer.class)))
.from(
select(count().as("c"))
.from(REQUIREMENT)
.where(REQUIREMENT.CREATOR_ID.equal(userId))
.unionAll(
select(count().as("c"))
.from(REQUIREMENT)
.where(REQUIREMENT.LEAD_DEVELOPER_ID.equal(userId)))
);
Alternatively, if you plan to add many more of these counts to the sum, this might be a faster option:
select(sum(choose()
.when(REQUIREMENT.CREATOR_ID.eq(userId)
.and(REQUIREMENT.LEAD_DEVELOPER_ID.eq(userId)), inline(2))
.when(REQUIREMENT.CREATOR_ID.eq(userId), inline(1))
.when(REQUIREMENT.LEAD_DEVELOPER_ID.eq(userId), inline(1))
.otherwise(inline(0))
))
.from(REQUIREMENT);
More details about the second technique in this blog post