How to dynamically count rows in a table from two another tables? - mysql

Question

I want to count rows in CHAT table that their REASON_ID column exist in REASON_GROUP table:
First table Chat:
ID REASON_ID DEPARTMENT_ID
1 46 1
2 46 1
3 50 1
4 50 2
5 100 1
6 100 2
Second table Reason:
ID REASON_NAME REASON_GROUP_ID
46 Reason1 1
50 Reason2 1
100 Reason3 2
101 Reason4 2
105 Reqson5 3
Third table Reason_Group :
ID NAME
1 Group1
2 Group2
3 Group3
I want to display result like this:
Reason1 Reason2 Reason3 Reason4 Reason5
2 2 2 0 0

Answer 1

You can use PIVOT and dynamic sql for that:
DECLARE #DynamicPivotQuery AS nvarchar(max)
DECLARE #ColumnName AS nvarchar(max)
--Get distinct values of the PIVOT Column
SELECT #ColumnName = ISNULL(#ColumnName + ',', '') + QUOTENAME(REASON_NAME)
FROM (SELECT DISTINCT REASON_NAME FROM Reason) AS Reasons
--Prepare the PIVOT query using the dynamic
SET #DynamicPivotQuery =
N'SELECT ' + #ColumnName + ' FROM
(
SELECT r.REASON_NAME, SUM(CASE WHEN c.ID is null OR rg.ID IS NULL THEN 0 ELSE 1 END) AS cnt
FROM Reason r
LEFT JOIN Chat c ON (c.REASON_ID = r.ID)
LEFT JOIN Reason_Group rg ON (r.REASON_GROUP_ID = rg.ID)
GROUP BY REASON_NAME
) inn
PIVOT(AVG(cnt)
FOR REASON_NAME IN (' + #ColumnName + ')) AS PVTTable'
--Execute the Dynamic Pivot Query
EXEC sp_executesql #DynamicPivotQuery
Result:
Reason1 Reason2 Reason3 Reason4 Reqson5
2 2 2 0 0
Actually you can do it without PIVOT, but you still have to use dynamic sql, I do not know how you can resolve your task without dynamic sql :(
So this is a solution without PIVOTING:
DECLARE #DynamicQuery AS nvarchar(max)
DECLARE #AgrColumns AS nvarchar(max)
--Get distinct values of the Column
SELECT #AgrColumns = ISNULL(#AgrColumns + ',', '') + 'SUM(CASE WHEN REASON_NAME = ''' + REASON_NAME + ''' THEN cnt ELSE 0 END) AS ' + QUOTENAME(REASON_NAME)
FROM (SELECT DISTINCT REASON_NAME FROM Reason) AS Reasons
--Prepare the query using the dynamic
SET #DynamicQuery =
N'SELECT ' + #AgrColumns + ' FROM
(
SELECT r.REASON_NAME, SUM(CASE WHEN c.ID is null OR rg.ID IS NULL THEN 0 ELSE 1 END) AS cnt
FROM Reason r
LEFT JOIN Chat c ON (c.REASON_ID = r.ID)
LEFT JOIN Reason_Group rg ON (r.REASON_GROUP_ID = rg.ID)
GROUP BY REASON_NAME
) inn'
--Execute the Dynamic Query
EXEC sp_executesql #DynamicQuery