Just by adding an index to a table doesn’t mean you get performance improvement.
To make query sargable by not altering the column side of Where predicate or join clause so that SQL Server can utilize the index on that column whithout having to do any extra work.
Non-Sargable Query example on dbo.Invetory table with 100 records:
</pre> Select Name FROM dbo.Inventory WHERE CONVERT(CHAR(10), CreateDate, 121) = '2018-06-28'
Here Sql Server will perform Index Scan on each row
Sargable Query example:
SELECT Name FROM dbo.Inventory WHERE CreateDate = CAST('2018-06-28' as datetime2)
Here Sql Server will perform Index Seek.