如何比较一行中两列之间的值（如果不同则创建另一行）？

Question

I have the following table in MySQL:

id | item_id | uom | uom1
1    1         kg    box

When i select all from the table, it will display one row.

I want to make it to display two row if the uom and uom1 is different.

For example, uom = kg and uom1 = box then result will show

id | item_id | uom
1    1         kg
2    1         box

if both uom and uom1 is same(kg) then only one row will show

id | item_id | uom
1    1         kg

Is it possible to do it using sql? Then i will just loop it at my view.

Answer 1

select 
  @rownum := @rownum + 1 AS id,
  T.* 
from (
    select  `item_id`, `uom`
    from Table1

    union

    select  `item_id`, `uom1` as `uom`
    from Table1
) T , (SELECT @rownum := 0) r

---

| id | item_id | uom |
|----|---------|-----|
|  1 |       1 |  kg |
|  2 |       1 | box |

---

DEMO SQL Fiddle

Answer 2

One simple way of doing it would be

select id, item_id, uom from tbl union
select id, item_id, uom1 from tbl

UNION will by default filter out duplicate lines. There is no need for further "tricks" ...

@Neeraj Wadhwa suggested the second line to be changed to:

select id, item_id, uom1 as uom from tbl

This is possible and will produce the same result, but it is not really necessary. The column names in a UNION construct will be determined by the first select statement anyway.

Answer 3

I think the simple union should help here:

select distinct * from (
  select id, item, uom1 as uom from stuff
    union
  select id, item, uom2 as uom from stuff
  ) as unionised
order by unionised.id

Hre's the fiddle: http://sqlfiddle.com/#!9/ece687/1