Welcome to today's post where we'll be diving into the world of SQL query debugging. We'll be unraveling a common mistake made by many developers and learn how to fix it. So, buckle up and let's get started!
Finding the Flaw
In our quest to uncover the root cause of
the issue, we will be dissecting a scenario where we need to retrieve all the
orders placed between June 1, 2014, and June 5, 2014. However, the initial SQL
query falls short of returning the expected results, leaving us with 9 records
instead of the anticipated 11.
Initial Query - Using the "BETWEEN" Clause
Our journey begins with the construction of
the initial query, utilizing the "BETWEEN" clause to filter the
results based on the order dates. However, a pitfall arises as we observe that
the output does not align with our expectations.
Database - AdventureWorksDW2022
Select SH.SalesOrderID, SH.ORDERDATE , SH.CUSTOMERID
FROM [Sales].[SalesOrderHeader] SH
WHERE ORDERDATE BETWEEN '2014-06-01' AND '2014-06-05'
Identifying the Missing Records
Upon realizing that two records are missing
from the result set, we delve deeper into the data to pinpoint the anomalies.
The comparison between the expected and actual output sheds light on the
absence of records with timestamps, highlighting a crucial oversight in our
initial approach.
Rectifying the Oversight
To address the issue, we experiment with an
alternate query, replacing the "BETWEEN" clause with "greater
than or equal to" and "less than or equal to" operators.
However, this endeavor also falls short, leading us to the revelation of the
timestamp values getting rounded up in the database, thus incorporating records
from June 6, which were not within our scope.
Select SH.ORDERDATE , SH.CUSTOMERID
FROM [Sales].[SalesOrderHeader] SH
WHERE ORDERDATE >= '2014-06-01' AND ORDERDATE <= '2014-06-05'
The Optimal Solution
Finally, we arrive at the most effective
approach, advocating for the removal of the time portion from both dates and
using the "less than" operator in conjunction with the next day's
date. This refined query yields the desired 11 records, providing us with a
seamless and accurate outcome.
Select SH.SalesOrderID, SH.ORDERDATE , SH.CUSTOMERID
FROM [Sales].[SalesOrderHeader] SH
WHERE CAST(ORDERDATE as date) BETWEEN '2014-06-01' AND '2014-06-05'
Conclusion
In wrapping up our debugging expedition,
we've not only unveiled a common misstep but also equipped ourselves with a
robust solution. As we embark on future SQL ventures, it's imperative to remain
vigilant of such nuances to ensure the integrity and precision of our queries.