Query Index for Dictionary Based Queries

Question

What would be the most efficient way to query and index for the following:

SELECT * Persons.LastName A-D
SELECT * Persons.LastName E-L
SELECT * Persons.LastN         


        

Answer 1

You predicate is sargable.

If you run this query on an indexed field:

SELECT  *
FROM    persons
WHERE   last_name >= 'a'
        AND last_name < 'e'

it produces the following plan:

  |--Nested Loops(Inner Join, OUTER REFERENCES:([MYDB].[dbo].[PERSONS].[ID]) OPTIMIZED)
       |--Index Seek(OBJECT:([MYDB].[dbo].[PERSONS].[IX_PERSONS_LAST_NAME]), SEEK:([MYDB].[dbo].[PERSONS].[LAST_NAME] >= 'a' AND [MYDB].[dbo].[PERSONS].[LAST_NAME] < 'E'),  WHERE:([MYDB].[dbo].[PERSONS].[LAST_NAME] like '[a-d]%') ORDERED FORWARD)
       |--Clustered Index Seek(OBJECT:([MYDB].[dbo].[PERSONS].[IX_PERSONS_LAST_NAME]), SEEK:([MYDB].[dbo].[PERSONS].[ID]=[MYDB].[dbo].[PERSONS].[ID]) LOOKUP ORDERED FORWARD)

which is equivalent to running this query:

SELECT  *
FROM    persons
WHERE   last_name >= 'a'
        AND last_name < 'e'