If not a duplicate row

Question

We are loading our data set using SSIS (bulk insert) to staging and the data may contain duplicate rows.
We are using the following query (grouped by WellID) to insert distinct rows:
INSERT INTO dbo.GasField ([Date], [Time], data1,
data2, data3, WellID)
SELECT DISTINCT [Date], [Time], data1, data2,
data3, w.WellID
FROM staging.GasAnalyser ga
INNER JOIN dbo.Well w
ON ga.Tag = w.Name
However, the dbo.GasField table may already contain a row in our data set. We therefore need to only insert if the row does not exist.
Note, the PK is WellID, [Date], [Time]
I believe we need to add a WHERE NOT EXISTS query and use the query below for retrieving duplicate records:
SELECT [Date], [Time], w.WellID
FROM staging.GasAnalyser ga
INNER JOIN dbo.Well w
ON ga.Tag = w.Name
GROUP BY [Date], [Time], w.WellID
HAVING COUNT(*) > 1

Answer 1

try this..... 
Method 1 
INSERT INTO dbo.GasField ([Date], [Time], data1, data2,
data3, WellID)
SELECT DISTINCT [Date], [Time], data1, data2,
data3, w.WellID 
FROM staging.GasAnalyser ga
INNER JOIN dbo.Well w
ON ga.Tag = w.Name
where not exists ( select WellID
from dbo.GasField GF where GF.WellID
 = w.WellID  and ga.Date
= GF.Date  and GA.time = GF.time)
Method 2 
WITH TempFG  ([Date], [Time], data1, data2,
data3, WellID)
AS
SELECT [Date], [Time], data1, data2,
data3, w.WellID , ROW_NUMBER() OVER(PARTITION by W.WellID,
[Date], [Time] ) as duplicate 
FROM staging.GasAnalyser ga
INNER JOIN dbo.Well w
ON ga.Tag = w.Name
INSERT INTO dbo.GasField ([Date], [Time], data1, data2,
data3, WellID)
select * from TempFG  
ramakrishna