How Can We Avoid Mixing UI Logic with Data Access in SQL Queries?

Common SQL anti-pattern: UI logic in data access layer

In the world of SQL, programmers often have difficulty reconciling the programming patterns they are familiar with in other languages ​​with the unique features of SQL. A common anti-pattern that arises from this transition is mixing UI logic in the data access layer.

Consider the following SQL 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 query fetches user information, mixing UI related formatting with data extraction. The programmer's intention may be to bind the dataset directly to the grid, but this creates some problems:

• Fragility: Query is tightly coupled to the UI layer. Any UI format changes require changes to the query.
• Hinders reusability: By consolidating UI logic into the data layer, queries become less reusable for other uses. The stored procedure using this query will also need to be changed to accommodate any UI changes.

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