LEFT JOIN Subtotal from the same TABLE - sql-server

Question

I am new to SQL, I am trying to query from a ledger table
I have two Queries that I need to join into one table
1st Query:
SELECT *
FROM TABLE 1
WHERE DATEDIFF(MONTH, [Transaction Date], GETDATE()) <= 3
AND [ITEMTYPE] = 'F-C'
AND ([Description] NOT LIKE '%REFILE%'
AND [Description] NOT LIKE '%CROSSOVER%')
AND ([UserNAME] LIKE '%USER1%'
OR [UserNAME] LIKE '%user2%'
OR [UserNAME] LIKE '%user3%')
2nd Query:
SELECT [ENCID], SUM([Trans]) AS Total_Charges
FROM Table 1
WHERE DATEDIFF(MONTH, [Transaction Date], GETDATE()) <= 3
AND [ITEMTYPE] IN ('C')
GROUP BY [ENCID];
I need to Left join the 2nd Query to the 1st Query on ENCID
THanks.

Answer 1

Well, you just join it. Nothing special about it, except that you have to remember to give an alias e.g. Totals
I have also changed your DATEDIFF(MONTH, [Transaction Date], GETDATE()) <= 3 to [Transaction Date] >= DATEADD(MONTH, -3, GETDATE()), to allow SQL Server to use indexes on [Transaction Date] column, if you have any.
Also leading wild card text searches e.g. [UserNAME] LIKE '%user2%' are slow, avoid them if you can: https://sqlperformance.com/2017/02/sql-indexes/seek-leading-wildcard-sql-server
SELECT *
FROM TABLE 1 AS a
LEFT JOIN
( SELECT [ENCID], SUM([Trans]) AS Total_Charges
FROM Table 1
WHERE [Transaction Date] >= DATEADD(MONTH, -3, GETDATE())
AND [ITEMTYPE] IN ('C')
GROUP BY [ENCID] ) AS Totals ON Totals.[ENCID] = a.[ENCID]
WHERE
[Transaction Date] >= DATEADD(MONTH, -3, GETDATE())
AND [ITEMTYPE] = 'F-C'
AND ([Description] NOT LIKE '%REFILE%'
AND [Description] NOT LIKE '%CROSSOVER%')
AND ([UserNAME] LIKE '%USER1%'
OR [UserNAME] LIKE '%user2%'
OR [UserNAME] LIKE '%user3%')

Answer 2

When you introduce any joins (to tables or subqueries) it is vital that you refer to columns from those sources by aliases.
SELECT t1.*
FROM TABLE_1 t1
LEFT JOIN (
SELECT [ENCID], SUM([Trans]) AS Total_Charges
FROM Table_1
WHERE [Transaction Date] >= DATEADD(month,-3,GETDATE())
AND [ITEMTYPE] IN ('C')
GROUP BY [ENCID]
) sq ON t1.[ENCID] = sq.[ENCID]
WHERE t1.[Transaction Date] >= DATEADD(month,-3,GETDATE())
AND t1.[ITEMTYPE] = 'F-C'
AND (t1.[Description] NOT LIKE '%REFILE%'
AND t1.[Description] NOT LIKE '%CROSSOVER%')
AND (t1.[UserNAME] LIKE '%USER1%'
OR t1.[UserNAME] LIKE '%user2%'
OR t1.[UserNAME] LIKE '%user3%')
NOTE: I have altered the way the dates are considered so that an index on [Transaction Date] could be utilized. Instead of calculating a number of months on every row, it is far more efficient to calculate a date then compare existing data to that value. For best performance try to avoid using functions on data in the where clause.