Postgresql – Postgres – How to get Multi-Count Query using a Where Clause for a Join Table

countjoin;postgresqlwhere

I have the following query that gets the counts across multiple tables that are joined:

select
    count(distinct e.planningitemdata->>'receiverDuns') as supplierOrCustomer,
    count(distinct e.planningitemdata->>'shipTo') as shipTo,
    count(distinct e.planningitemdata->>'productId') as product,
    count(distinct eo.orderlineid) as orderline,
    count(distinct e.planningitemid) as planningitem 
from
    eventplanningitem e 
join
    eventorderline eo 
        on e.eventid = eo.eventid
join
    orderline o 
        on eo.orderlineid = o.id
        and o.deliveryrequesteddate between '2018-03-06' AND '2018-05-06'
where
    e.eventId = '9f6d3d50-05ca-4441-a4e4-24de2b52de5b'

I want to filter the "orderlineid" counts based on a date filter, but my issue is that when I try to apply it to the join as shown above, it 0's out all the results of all the other counts. Same thing happens if I try to add a where clause to the end. If I make the orderline table a left outer join, I get the count of the orderlines that don't match the date criteria.

Result:

0;0;0;0;0

A similar version produces the same thing:

select
        count(distinct e.planningitemdata->>'receiverDuns') as supplierOrCustomer,
        count(distinct e.planningitemdata->>'shipTo') as shipTo,
        count(distinct e.planningitemdata->>'productId') as product,
        count(distinct eo.orderlineid) as orderline,
        count(distinct e.planningitemid) as planningitem 
    from
        eventplanningitem e 
    join
        eventorderline eo 
            on e.eventid = eo.eventid
    join
        orderline o 
            on eo.orderlineid = o.id
            and o.deliveryrequesteddate between '2018-03-06' AND '2018-05-06'
    where
        e.eventId = '9f6d3d50-05ca-4441-a4e4-24de2b52de5b' 
        and (o.deliveryrequesteddate >='2018-03-06' and o.deliveryrequesteddate <= '2018-05-06')

I get counts if I make the orderline join a left outer join, but it includes the orderLine records that actually fall outside the date criteria so it's also not correct.

I want to avoid breaking this into multiple queries but I wanted to check if I'm missing something before going that route.

Best Answer

An alternative @RDFozz's answer would be to use FILTER:

count(distinct eo.orderlineid) filter 
    (where o.deliveryrequesteddate between '2018-03-06' AND '2018-05-06') 
    as orderline,

I think it is bit more intuitive, as this is the exact reason for FILTER to exist so its intention is more obvious than using CASE.

Related Solutions

Mysql – How to simulate a table join on itself

You'll need to first create a list of every product_number and date combination. You can do this using a CROSS JOIN of your table:

select distinct p.product_number, d.date
from yourtable p
cross join yourtable d;

See SQL Fiddle with Demo. This will create a list of data similar to:

| PRODUCT_NUMBER |                            DATE |
|----------------|---------------------------------|
|            100 |  January, 01 2010 00:00:00+0000 |
|            200 |  January, 01 2010 00:00:00+0000 |
|            100 | February, 01 2010 00:00:00+0000 |

You will then use the above query and LEFT JOIN to your table to return the final result:

select 
  pd.product_number,
  pd.date,
  t.value
from
(
  -- list of every product/date
  select distinct p.product_number, d.date
  from yourtable p
  cross join yourtable d
) pd
left join yourtable t
  on pd.date = t.date
  and pd.product_number = t.product_number
order by pd.product_number, pd.date;

See SQL Fiddle with Demo. Giving a final result of:

| PRODUCT_NUMBER |                            DATE |  VALUE |
|----------------|---------------------------------|--------|
|            100 |  January, 01 2010 00:00:00+0000 |      1 |
|            100 | February, 01 2010 00:00:00+0000 |      1 |
|            100 |    March, 01 2010 00:00:00+0000 |      1 |
|            200 |  January, 01 2010 00:00:00+0000 |      1 |
|            200 | February, 01 2010 00:00:00+0000 | (null) |
|            200 |    March, 01 2010 00:00:00+0000 |      1 |

The LEFT JOIN returns all rows from your list of products and dates regardless of whether a matching row exists in the other table.

This could also be written as:

select 
  p.product_number,
  d.date,
  t.value
from
(
  -- list of every product
  select distinct product_number
  from yourtable 
) p  
cross join
( 
  -- list of every date
  select distinct date
  from yourtable 
) d
  -- then join to the table
left join yourtable t
  on  d.date = t.date
  and p.product_number = t.product_number
order by p.product_number, d.date ;

See SQL Fiddle with Demo. This may have better performance depending on your table size.

Now if you wanted to return a list of all dates, regardless of whether or not they appear in the table, then I would suggest creating a table of dates. This table would be used in a similar manner to create a list of all dates/products which you would then join.

The table would be similar to:

CREATE TABLE dates
    (`date` datetime)
;

INSERT INTO dates
    (`date`)
VALUES
    ('2010-01-01 00:00:00'),
    ('2010-02-01 00:00:00'),
    ('2010-03-01 00:00:00'),
    ('2010-04-01 00:00:00'),
    ('2010-05-01 00:00:00')
;

You'd then use the following query to get the list of dates/products:

select distinct p.product_number, d.date
from yourtable p
cross join dates d

And finally, you would join that back to your table:

select 
  pd.product_number,
  pd.date,
  t.value
from
(
  -- list of every product/date
  select distinct p.product_number, d.date
  from yourtable p
  cross join dates d
) pd
left join yourtable t
  on pd.date = t.date
  and pd.product_number = t.product_number
order by pd.product_number, pd.date;

See SQL Fiddle with Demo. Or an alternative:

select 
  p.product_number,
  d.date,
  t.value
from
(
  -- list of every product
  select distinct product_number
  from yourtable 
) p  
cross join
 dates
  d
  -- then join to the table
left join yourtable t
  on  d.date = t.date
  and p.product_number = t.product_number
order by p.product_number, d.date ;

See SQL Fiddle with Demo. Again this may have better performance based on the table size. Using this type of solution, you'd return all dates even those not in your table:

| PRODUCT_NUMBER |                            DATE |  VALUE |
|----------------|---------------------------------|--------|
|            100 |  January, 01 2010 00:00:00+0000 |      1 |
|            100 | February, 01 2010 00:00:00+0000 |      1 |
|            100 |    March, 01 2010 00:00:00+0000 |      1 |
|            100 |    April, 01 2010 00:00:00+0000 | (null) |
|            100 |      May, 01 2010 00:00:00+0000 | (null) |
|            200 |  January, 01 2010 00:00:00+0000 |      1 |
|            200 | February, 01 2010 00:00:00+0000 | (null) |
|            200 |    March, 01 2010 00:00:00+0000 |      1 |
|            200 |    April, 01 2010 00:00:00+0000 | (null) |
|            200 |      May, 01 2010 00:00:00+0000 | (null) |

Sql-server – Effect of where statement in subquery (to get rid of unnecessary join)

Perhaps it is easier to see with the aid of some rewrites. Your first query can be rewritten to (using the same alias at different levels makes it a bit difficult to understand):

select * 
from parent p1
where exists (
  select 1  
  from parent p2
  join child c on c.parentId = p2.id
  where p2.age > 50
    and p1.id = p2.id 
)

Assuming id is unique in parent this can be rewritten as:

select * 
from parent p1
where exists (
  select 1  
  from child c 
  where c.parentId = p1.id
    and p1.age > 50
)

which in turn can be rewritten to your query.

So you can eliminate the join against parent inside the sub-select. However, your second query is a bit difficult to understand as it is written. I would suggest (I'm guessing your intention)

select * 
from parent p1
where exists (
  select 1  
  from child c 
  where c.parentId = p1.id
)
and p1.age > 50

If parent.id is not unique the above wont hold

Best Answer

Related Solutions

Mysql – How to simulate a table join on itself

Sql-server – Effect of where statement in subquery (to get rid of unnecessary join)

Related Question