Merge multiple select statements and group them - sql

Question

I am having trouble to find an efficient solution to my problem. I think this is a fairly common issue, that is why I am asking it out here.
Here is the problem.
Let says I have multiple selects such as the following ones :
SELECT CREATE
date
num_created
01-01-2021
10
01-02-2021
2
01-04-2021
13
SELECT Update
date
num_update
01-01-2021
14
01-02-2021
2
01-03-2021
9
SELECT Delete
date
num_delete
01-02-2021
2
01-05-2021
40
I want to have this final output
Final output
date
num_created
num_update
num_deleted
01-01-2021
10
14
0
01-02-2021
2
2
2
01-03-2021
0
9
0
01-04-2021
13
0
0
01-05-2021
0
0
40
*I can't assume that any table has all the dates or have matching dates

Answer 1

It looks like you want count grouped by days:
select
tbls.date,
sum(tbls.num_created) as num_created,
sum(tbls.num_updated) as num_updated,
sum(tbls.num_deleted) as num_deleted
from (
select date, num_created, 0 as num_updated, 0 as num_deleted from tbl_create
union all
select date, 0 as num_created, num_updated, 0 as num_deleted from tbl_update
union all
select date, 0 as num_created, 0 as num_updated, num_deleted from tbl_delete) as tbls
group by tbls.date
Please don't abuse "with statement" when it is not needed (as seen in the other answers).
Edit - extra simple query:
if object_id('tempdb..#tmp_dml_statement') is not null drop table #tmp_dml_statement
select date, num_created, 0 as num_updated, 0 as num_deleted
into #tmp_dml_statement
from tbl_create
union all
select date, 0 as num_created, num_updated, 0 as num_deleted
from tbl_update
union all
select date, 0 as num_created, 0 as num_updated, num_deleted
from tbl_delete

Answer 2

You can perform full outer join between the tables and case statement to choose the date as below (Assume 3 tables/queries as a, b, c):
With temp as
(
select case when a.date is not null then a.date else b.date end as date,num_created,num_update from a full join b on (a.date=b.date)
),
temp1 as
(
select case when temp.date is not null then temp.date else c.date end as date,num_created,num_update,num_delete from temp full join c on (temp.date=c.date)
)
select * from temp1;

Answer 3

assume the tables are:
tbl_create(dt, num_created)
tbl_update(dt, num_updated)
tbl_delete(dt, num_deleted)
start with a (temporary)table that contains all dates from the 3 source tables: all_dates
then (left outer) join the counters from the 3 source tables.
note: 'union' removes duplicates, no need to worry about that (in contrast to 'union all')
note: coalesce(a,b) returns the first non-null parameter, so you have zeroes rather than 'null's
with all_dates(dt) as (
select dt from tbl_create
union
select dt from tbl_update
union
select dt from tbl_delete
)
select all_dates.dt
, coalesce(tbl_create.num_created,0) --
, coalesce(tbl_update.num_updated,0)
, coalesce(tbl_delete.num_deleted,0)
from all_dates
left outer join tbl_create on all_dates.dt = tbl_create.dt
left outer join tbl_update on all_dates.dt = tbl_update.dt
left outer join tbl_delete on all_dates.dt = tbl_delete.dt