Is there a way to only show first non-zero value but if all values are zero then show 1st instance of a column in a separate table from joining tables

Question

These two tables are quite large, and my select statement has more values I am obtaining, but I think I can simplify this data and query so my question can be answered.

Here is my select statement:

SELECT invoice.InvoiceNum, Layer, InvoiceItemNum 
FROM (INVOICE 
        left outer join InvoiceItem item 
            ON item.InvoiceNum = Invoice.InvoiceNum
    ) 
ORDER BY invoice.InvoiceNum

So I have two tables. An Invoice table and an InvoiceItem table. They are joined by the InvoiceNum column in each table, and displaying the InvoiceNum and Layer Column

Here is a result to this query:

InvoiceNum  | Layer | InvoiceItemNum
1           | 10    | 1
1           | 0     | 2
1           | 7     | 3 
1           | 0     | 4 
2           | 0     | 1
2           | 3     | 2 
3           | 0     | 1
3           | 0     | 2
3           | 0     | 3 
4           | 0     | 1
4           | 0     | 2
4           | 5     | 3

Since my InvoiceItem table has multiple rows that can be assigned to 1 InvoiceNum this is causing me to have duplicate invoiceNums in my result, which I do not want.

Here is the result I am trying to get, only listing 1 invoiceNum from the Invoice table, with the first case of a non-zero value from the InvoiceItem table's layer column, and If there is no non-zero than list the first zero.

Trying for something like this:

InvoiceNum  | Layer | InvoiceItemNum
1           | 10    | 1
2           | 3     | 2 
3           | 0     | 1
4           | 5     | 3

I am just not sure how to do this or if this is possible given that these are on two different tables.

Answer 1

this question is a bit tricky:

Try this in Postgres:

with cte as (
select 
inv.invoicenum,sum(layer::int) "sum_layer"
from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
group by 1
)
,
cte1 as (

select distinct on (inv.invoicenum) inv.invoicenum,layer, InvoiceItemNum

from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
where inv.invoicenum in (select invoicenum from cte where sum_layer=0)
order by inv.invoicenum, InvoiceItemNum
),
cte2 as (
select 
distinct on (inv.invoicenum) inv.invoicenum, layer , InvoiceItemNum
from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
where inv.invoicenum in (select invoicenum from cte where sum_layer>0) and layer::int>0
order by inv.invoicenum, InvoiceItemNum
)
(
select * from cte1
union all
select * from cte2
)
order by 1

DEMO

In MySQL 8:

Try This:

with cte as (
select 
inv.invoicenum,sum(layer) "sum_layer"
from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
group by 1
)
,
cte1 as (
select * from (
select inv.invoicenum, layer, InvoiceItemNum
from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
where inv.invoicenum in (select invoicenum from cte where sum_layer=0)
order by inv.invoicenum, InvoiceItemNum
) c
group by invoicenum
),
cte2 as (
select * from (
select inv.invoicenum, layer, InvoiceItemNum
from invoice inv inner join invoiceitem item on item.invoicenum=inv.invoicenum
where inv.invoicenum in (select invoicenum from cte where sum_layer>0) and layer>0
order by inv.invoicenum, InvoiceItemNum ) c
group by invoicenum
)
(
select * from cte1
union all
select * from cte2
)

Answer 2

Assumptions/Understandings:

• while tagged with sybase the question does not distinguish between the 4x different Sybase RDBMS products ( ASE , SQLAnywhere , IQ , Advantage ) so I'm going to stick with what should be general SQL syntax (ie, the 4x products have different SQL dialects; also, ASE does not support CTEs)
• I don't understand OP's use of left (outer) join since the provided output doesn't appear to indicate any 'missing' rows from InvoiceItem
• it's not clear which table the Layer and InvoiceItemNum columns belong to so I'm going to assume they belong to InvoiceItem

Guessing at a set of minimum table definitions and associated insert statements:

create table Invoice
(InvoiceNum     int
)

create table InvoiceItem
(InvoiceNum     int
,InvoiceItemNum int
,Layer          int
)

insert Invoice select 1 union all select 2 union all select 3 union all select 4

insert InvoiceItem values (1,1,10)
insert InvoiceItem values (1,2,0)
insert InvoiceItem values (1,3,7)
insert InvoiceItem values (1,4,0)

insert InvoiceItem values (2,1,0)
insert InvoiceItem values (2,2,3)

insert InvoiceItem values (3,1,0)
insert InvoiceItem values (3,2,0)
insert InvoiceItem values (3,3,0)

insert InvoiceItem values (4,1,0)
insert InvoiceItem values (4,2,0)
insert InvoiceItem values (4,3,5)

Query that generates OP's current output:

select  inv.InvoiceNum,
        item.Layer,
        item.InvoiceItemNum
from    Invoice inv
left                          -- superfluous in this case?
join    InvoiceItem item
on      inv.InvoiceNum = item.InvoiceNum
order by 1,3

 InvoiceNum  Layer       InvoiceItemNum
 ----------- ----------- --------------
           1          10              1
           1           0              2
           1           7              3
           1           0              4
           2           0              1
           2           3              2
           3           0              1
           3           0              2
           3           0              3
           4           0              1
           4           0              2
           4           5              3

A couple different (convolued, messy) ideas for generating OP's desired output:

-- join based on Layer!=0; if no rows found then override NULLs
-- with Layer=0 and InvoiceItemNum=min(InvoiceItemNum) where Layer=0;
-- needs more work in case there are no matching rows in InvoiceItem ...
-- wrap case/then in a coalesce() and set to, what, 0?

select  inv.InvoiceNum,
        coalesce(item1.Layer,0) as "Layer",
        case    when item1.InvoiceItemNum is NULL
                then (select min(InvoiceItemNum) from InvoiceItem item3 where item3.InvoiceNum = inv.InvoiceNum)
                else item1.InvoiceItemNum
        end as "InvoiceItemNum"

from    Invoice inv
left
join    InvoiceItem item1
on      inv.InvoiceNum = item1.InvoiceNum
and     item1.Layer != 0
and     not exists(select       1
                   from         InvoiceItem item2
                   where        item2.InvoiceNum = item1.InvoiceNum
                   and          item2.Layer != 0
                   and          item2.InvoiceItemNum < item1.InvoiceItemNum)
order by 1

-- OR

-- perform a mutually exclusive UNION of Layer!=0 and Layer=0 queries
-- with Layer!=0 having prcedence

select  inv.InvoiceNum,
        item1.Layer,
        item1.InvoiceItemNum

from    Invoice inv
--left  ??? needs work if this is really an outer join ???
join    InvoiceItem item1
on      inv.InvoiceNum = item1.InvoiceNum

and     (
         (      item1.Layer != 0
          and   not exists(select 1
                           from   InvoiceItem item2
                           where  item2.InvoiceNum = item1.InvoiceNum
                           and    item2.Layer != 0
                           and    item2.InvoiceItemNum < item1.InvoiceItemNum)
         )

         or

         (      item1.Layer = 0
          and   not exists(select 1
                           from   InvoiceItem item3
                           where  item3.InvoiceNum = item1.InvoiceNum
                           and    item3.Layer != 0)
          and   not exists(select 1
                           from   InvoiceItem item4
                           where  item4.InvoiceNum = item1.InvoiceNum
                           and    item4.Layer = 0
                           and    item4.InvoiceItemNum < item1.InvoiceItemNum)
         )
        )
order by 1

Both of these generate:

 InvoiceNum  Layer       InvoiceItemNum
 ----------- ----------- --------------
           1          10              1
           2           3              2
           3           0              1
           4           5              3

NOTES:

• not sure what the output should be since it doesn't appear (to me) OP has demonstrated the need for the left (outer) join
• all queries tested in (Sybase)SAP ASE 16.0

Answer 3

have you tried ASC and DESC?

SELECT invoice.InvoiceNum, Layer, InvoiceItemNum 
FROM (INVOICE 
        left outer join InvoiceItem item 
            ON item.InvoiceNum = Invoice.InvoiceNum
    ) 
ORDER BY Layer DESC, invoice.InvoiceNum ASC