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SQL Query Optimization: Understanding BETWEEN vs. = and >=

In SQL Server 2000 and 2005, database programmers often face the dilemma of choosing between the BETWEEN operator and the combination of <= and >= in their WHERE clauses. Understanding the functionality and usage scenarios of each is crucial for optimizing query performance.

BETWEEN Operator

The BETWEEN operator is a shorthand syntax that combines the functionality of <= and >=. For example, the query:

SELECT EventId, EventName
FROM EventMaster
WHERE EventDate BETWEEN '10/15/2009' AND '10/18/2009'

is equivalent to the following syntax using <= and >=:

SELECT EventId, EventName
FROM EventMaster
WHERE EventDate >= '10/15/2009' AND EventDate <= '10/18/2009'

Usage Scenarios

When both end values (inclusive) need to be included in the result set, the BETWEEN operator should be used for its simplicity and readability. This is particularly useful when dealing with date ranges.

Long Syntax

In scenarios where one or both end values need to be excluded from the result set, the long syntax using <= and >= is preferred. For example, to exclude events on 10/18/2009:

SELECT EventId, EventName
FROM EventMaster
WHERE EventDate >= '10/15/2009' AND EventDate < '10/18/2009'

Datetime Handling

It's important to note that when dealing with DATETIME fields, both BETWEEN and <=/>= operators compare time components as well. To ensure accurate results, ensure that the date ranges include the desired time components. For example:

SELECT EventId, EventName
FROM EventMaster
WHERE EventDate BETWEEN '2009-10-15 00:00' AND '2009-10-18 23:59:59'

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