Combining data in SQL Union syntax - mysql

Question

I'm doing a SQL Union syntax and I wanted to have a result like this:
+---------------+-----+---------+
|trkBusinessUnit| New | Pending |
+---------------+-----+---------+
| AIIB 2 0 |
| Credit Control 1 3 |
| Direct Center 1 2 |
| Financial Ins 1 1 |
| Motor Acclaim 1 0 |
+-------------------------------+
from my code:
SELECT trkBusinessUnit, Count(*) as New,0 as Pending
FROM tblDTPTracker
WHERE trkStatus = 'New'
GROUP BY trkBusinessUnit
UNION
SELECT trkBusinessUnit,0 as New,Count(*) as Pending
FROM tblDTPTracker
WHERE trkStatus = 'Pending'
GROUP BY trkBusinessUnit
but then the current output is:
+---------------+-----+---------+
|trkBusinessUnit| New | Pending |
+---------------+-----+---------+
| AIIB 2 0 |
| Credit Control 1 0 |
| Credit Control 0 3 |
| Direct Center 1 0 |
| Direct Center 0 2 |
| Financial Ins 1 0 |
| Financial Ins 0 1 |
| Motor Acclaim 1 0 |
+-------------------------------+
Am I missing out something or doing something wrong? Kindly advise.

Answer 1

There are (or has been) some syntax issues in the previous answers, but the intent of both earlier answers is correct, you need to use a GROUP BY query and NOT use UNION - which simply does not do what you were hoping/expecting.
UNION or UNION ALL work ROW by ROW, and absolutely do NOT merge by COLUMN
So, the MySQL syntax for the group by based query could be any of these:
COUNT() using an implicit NULL
SELECT
trkBusinessUnit
, COUNT(CASE WHEN trkStatus = 'New' THEN 1 END) as New
, COUNT(CASE WHEN trkStatus = 'Pending' THEN 1 END) as Pending
FROM tblDTPTracker
GROUP BY trkBusinessUnit
;
COUNT() using explicit NULL
SELECT
trkBusinessUnit
, COUNT(CASE WHEN trkStatus = 'New' THEN 1 ELSE NULL END) as New
, COUNT(CASE WHEN trkStatus = 'Pending' THEN 1 ELSE NULL END) as Pending
FROM tblDTPTracker
GROUP BY trkBusinessUnit
;
SUM() as an alternative to counting:
select
trkBusinessUnit
, sum(case when trkStatus = 'New' then 1 else 0 end) as New
, sum(case when trkStatus = 'Pending' then 1 else 0 end) as Pending
from tblDTPTracker
where trkStatus in ('Pending', 'New')
group by trkBusinessUnit
;
Apologies to both Marc Gravell & Daniel Gadawski who preceded this answer; this answer is a derivative of yours.
See this SQLFiddle demo of these queries

Answer 2

If I understand you correctly, you don't have to use an union.
Try:
SELECT
trkBusinessUnit,
COUNT(CASE WHEN trkStatus = 'New' THEN 1 ELSE NULL END) as New,
COUNT(CASE WHEN trkStatus = 'Pending' THEN 1 ELSE NULL END) as Pending
FROM tblDTPTracker
GROUP BY trkBusinessUnit

Answer 3

Union appends rows vertically (noting that UNION also takes only the distinct rows; UNION ALL takes all rows). What you want is either a full outer join of two sub-queries, or a more complicated select. I'd go with the latter!
select tblDTPTracker,
sum(case trkStatus when 'New' then 1 else 0 end) as New,
sum(case trkStatus when 'Pending' then 1 else 0 end) as Pending
from tblDTPTracker
where trkStatus in ('Pending', 'New')
group by tblDTPTracker
The full outer join approach would be something like:
SELECT ISNULL(x.trkBusinessUnit, y.trkBusinessUnit) as trkBusinessUnit,
ISNULL(x.New, 0) as New,
ISNULL(y.Pending, 0) as Pending
FROM (
SELECT trkBusinessUnit, Count(1) as New
FROM tblDTPTracker
WHERE trkStatus = 'New'
GROUP BY trkBusinessUnit) x
FULL OUTER JOIN (
SELECT trkBusinessUnit, Count(1) as Pending
FROM tblDTPTracker
WHERE trkStatus = 'Pending'
GROUP BY trkBusinessUnit) y on y.trkBusinessUnit = x.trkBusinessUnit