This is the second installment in a two-part blog series exploring T-SQL user-defined functions. We build upon foundational concepts introduced in Part 1 to examine practical applications and implementation strategies.

Function Types and Performance Considerations

There are two function categories: table-valued and scalar. Table-valued functions are recommended for most scenarios because they usually perform more efficiently (run faster) and handle large datasets very well. While scalar functions return only a single value, table-valued variants can return multiple rows functioning as traditional table data. However, these functions carry limitations: they cannot accommodate dynamic SQL or invoke other functions.

The DRY Principle

The core recommendation follows the DRY (don't repeat yourself) software development principle. Rather than duplicating code across multiple procedures, functions serve as centralized logic repositories. This approach delivers three key benefits:

• Uniformity: Functions establish coding standards across organizational systems
• Maintenance Efficiency: Bug fixes applied to a function automatically propagate to all dependent code
• Scalability: Developers avoid rewriting identical logic throughout corporate databases

Practical Provider Data Example

To illustrate these concepts, consider a provider information use case. In MEDITECH version 6.1x, retrieving common provider details requires joining eight separate tables. A table-valued function "flattens" this complex query structure, eliminating repetitive code whenever provider data is needed.

Single-statement, in-line table-valued functions typically deliver optimal performance across varying dataset sizes.

Function Advantages Summary

Functions enable organizations to:

• Eliminate coding repetition across systems
• Implement standardized development practices
• Simplify complex multi-table structures
• Improve efficiency organization-wide
• Abstract intricate logic for reusable application