Get aggregate sum of difference of two dates in JOOQ - postgresql

Question

I am using JOOQ for writing SQL in my java code.I have following query written into the PostgreSQL database:'
Query: Fetches the total number of checked task and the total time taken to complete the tasks.
Total time for a task is calculated from table "workevents" by doing (endtime-starttime).But here I am fetching the total time spent on all the tasks.
with taskdata as (
select taskid from unittest.tasks
where projectname='test'and status='checked'
),
workevents as(
select (endtime-starttime) diff ,unittest.workevents.taskid as
workeventtaskid from unittest.workevents ,taskdata
where taskdata.taskid=unittest.workevents.taskid
)
select sum(workevents.diff),count(distinct workeventtaskid) from
workevents;
I have converted it into the jooQ AS below:
final String sql =
with(TASK_INFO_WRAPPER)
.as(select(TASK_ID).from(TASK_TABLE)
.where(PROJECT_NAME.eq(param()).and(TASK_STATUS.eq("checked"))))
.with(WORKEVENT_INFO_WRAPPER)
.as(select(TASK_END_TIME.sub(TASK_START_TIME).as("diff"),
WORKEVENT_TASK_ID.as("workeventtaskid"))
.from(WORKEVENT_TABLE, table(name(TASK_INFO_WRAPPER)))
.where("workeventinfo.taskid=taskinfo.taskid"))
.select().getSQL(ParamType.INDEXED);
But I am not able to get the aggregate sum of the "diff"(difference of the dates).Is there any function in JOOQ that can convert sql statement "select sum(workevents.diff)" into JOOQ.
I have tried sum(field) function but its giving compile time error because sum is used for numbers.
and Here I am calculating the accumulative sum of the difference of the two dates(diff).

Answer 1

All RDBMS behave subtly differently when implementing a date difference using the - operator, which is why it is generally recommended to use jOOQ's DSL.dateDiff() or DSL.timestampDiff() instead.
A side note on using WITH
WITH is often used to decompose a problem into smaller problems in SQL. But at some point, that decomposition leads to more complicated queries than necessary, as in your case. Especially when using jOOQ, it is often recommended to avoid common table expressions (WITH) or derived tables, not only because they're a bit more difficult to express in jOOQ, but also because they don't really add value to your query.
Your query could be written like this instead:
select
sum(e.endtime - e.starttime),
count(distinct e.taskid)
from unittest.tasks t
join unittest.workevents e on t.taskid = e.taskid
where t.projectname = 'test' and t.status = 'checked'
And that would obviously be quite easier to translate to jOOQ.