What are the most effective query design patterns?

1 Use subqueries

Subqueries are queries nested within other queries. They can be used to filter, aggregate, or join data from multiple tables or sources. Subqueries can simplify complex queries, avoid duplication, and improve performance by reducing the number of rows processed. However, subqueries can also introduce challenges such as readability, debugging, and optimization. Therefore, you should use subqueries wisely and follow some best practices, such as using aliases, limiting the scope, and choosing the right type of subquery (correlated or uncorrelated).

3 Use window functions

Window functions are functions that operate on a subset of rows within a query result, called a window. They can be used to perform calculations or transformations that depend on the context or order of the rows, such as ranking, partitioning, aggregating, or lagging. Window functions can enhance the functionality, efficiency, and clarity of your queries by avoiding joins, subqueries, or loops, and by expressing complex logic in a concise way. However, window functions can also affect performance and compatibility, so you should use them appropriately and test them thoroughly.

4 Use set operators

Set operators are operators that combine the results of two or more queries into one result set. They can be used to perform set operations such as union, intersection, difference, or symmetric difference. Set operators can simplify and optimize your queries by eliminating duplicates, merging data, or finding common or distinct values. However, set operators can also introduce errors and limitations, such as requiring compatible data types, columns, and order, and ignoring null values. Therefore, you should use set operators correctly and compare them with other alternatives.

5 Use stored procedures

Stored procedures are precompiled and reusable blocks of SQL code that can be executed by a database server. They can be used to encapsulate business logic, implement security, enforce consistency, and automate tasks. Stored procedures can improve performance, security, and maintainability of your queries by reducing network traffic, preventing SQL injection, and centralizing code. However, stored procedures can also introduce complexity and dependency, such as requiring testing, debugging, and documentation, and affecting portability and flexibility. Therefore, you should use stored procedures judiciously and follow some best practices, such as using parameters, comments, and error handling.

6 Use query hints

Query hints are optional instructions that you can provide to the database engine to influence how a query is executed. They can be used to override the default behavior or optimize the query plan, such as choosing a specific index, join type, or locking strategy. Query hints can improve performance, reliability, and control of your queries by resolving issues, enforcing requirements, or exploiting opportunities. However, query hints can also introduce risks and drawbacks, such as causing errors, conflicts, or side effects, and affecting maintainability and scalability. Therefore, you should use query hints sparingly and carefully, and only after analyzing the query and the data.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?