SQL Query to Combine rows - sql

Question

I have a query that currently prints out what I need but doesn't combine the rows that I need. For example, I need the first two rows with the meter name to be combined together and so on for the rest of the meter names.
This is currently what I have:
SELECT
--Displays Client Number
CASE
WHEN v.MID IS NULL THEN ''
ELSE v.ClientNumber
END AS 'Client Number',
--Displays MID Number
CASE
WHEN v.MID IS NULL THEN ''
ELSE v.MID
END AS MID,
--Displays Meter Name
CASE
WHEN v.MID IS NULL THEN ''
ELSE v.MeterName
END AS 'Meter Name',
/*
CASE
WHEN v.MID IS NULL THEN 0
ELSE SUM(v.MCF)
END AS MCF,
*/
--Displays January's MCF
CASE
WHEN v.AccountPeriod = '2018-01-01' THEN SUM(v.MCF)
ELSE 0
END AS January,
--Displays Febuary's MCF
CASE
WHEN v.AccountPeriod = '2018-02-01' THEN SUM(v.MCF)
ELSE 0
END AS Febuary,
CASE
WHEN v.MID IS NULL THEN 0
ELSE SUM(v.mcf)
END AS 'Meter Total'
FROM Volumes v
LEFT JOIN CurrentMeters cm
ON v.MID = cm.MID
WHERE cm.ClientNumber = 107500
GROUP BY v.MID, v.AccountPeriod, v.ClientNumber, v
Does anyone have any suggestions as to what I should do or how I should approach this?

Answer 1

I think you just want conditional aggregation:
SELECT (CASE WHEN v.MID IS NULL THEN '' ELSE v.ClientNumber END) AS Client_Number,
COALESCE(WHEN v.MID, '') as MID,
(CASE WHEN v.MID IS NULL THEN '' ELSE v.MeterName END) AS Meter_Name,
SUM((CASE WHEN v.MID IS NULL THEN 0 v.MCF END) AS MCF,
SUM(CASE WHEN v.AccountPeriod = '2018-01-01' THEN v.MCF ELSE 0 END) AS January,
SUM(CASE WHEN v.AccountPeriod = '2018-02-01' THEN v.MCF ELSE 0 END) AS January,
SUM(CASE WHEN v.MID IS NULL THEN 0 ELSE v.mcf END) AS Meter_Total
FROM Volumes v JOIN
CurrentMeters cm
ON v.MID = cm.MID
WHERE cm.ClientNumber = 107500
GROUP BY (CASE WHEN v.MID IS NULL THEN '' ELSE v.ClientNumber END),
COALESCE(WHEN v.MID, ''),
(CASE WHEN v.MID IS NULL THEN '' ELSE v.MeterName END);
Notes:
Your WHERE clause is turning the outer join into an inner join, so there is no reason to express an outer join.
The GROUP BY keys specify what defines a row in the result set. Each combination of unique values in the data is in exactly one row. Hence, you don't want AccountPeriod in the GROUP BY.
Presumably, you want one row for each of the expressions that define a row, so these expressions are in the group by.
For conditional aggregation, the CASE expression is an argument to an aggregation function such as SUM().