How Can We Avoid the Pitfalls of Mixing UI Logic and Data Access in SQL Queries?

The Risks of Combining Data and Presentation Logic in SQL

Relational database interactions demand a shift from typical programming practices. A common and damaging error is blending user interface (UI) logic directly into SQL data access queries.

Observe the following example query:

<code class="language-sql">SELECT
    FirstName + ' ' + LastName as "Full Name",
    CASE UserRole
        WHEN 2 THEN "Admin"
        WHEN 1 THEN "Moderator"
        ELSE "User"
    END as "User's Role",
    CASE SignedIn
        WHEN 0 THEN "Logged in"
        ELSE "Logged out"
    END as "User signed in?",
    CONVERT(VARCHAR(100), LastSignOn, 101) as "Last Sign On",
    DATEDIFF(day, LastSignOn, GETDATE()) as "Days since last sign on",
    AddrLine1 + ' ' + AddrLine2 + ' ' + AddrLine3 + ' ' +
        City + ', ' + State + ' ' + Zip as "Address",
    'XXX-XX-' + SUBSTRING(
        CONVERT(VARCHAR(9), SSN), 6, 4) as "Social Security #"
FROM Users</code>

This approach creates several problems. The tight coupling between data retrieval and UI formatting makes the query fragile and difficult to maintain. The embedded formatting logic also reduces the reusability of the query or any potential stored procedures.

Separating UI logic from data access improves code stability, simplifies complexity, and increases flexibility.

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