83 ) Best Practices for SQL Queries

 

10 Best Practices for SQL Queries

1. Select Only Needed Columns

   Never use SELECT *. Always list the specific columns you need to save memory and network speed.

2. Filter Data Early (Use WHERE)

   Put conditions in the WHERE clause instead of HAVING whenever possible. This filters rows before grouping happens.

3. Avoid Functions on Indexed Columns

   Do not wrap columns in functions like YEAR(OrderDate) = 2026. It disables indexes and forces a slow full table scan.

4. Use Proper Joins Instead of Subqueries

   Use explicit INNER JOIN or LEFT JOIN instead of nested subqueries. Joins are usually easier for the database engine to optimize.

5. Index Frequently Searched Columns

   Add indexes to columns used often in WHERE, JOIN, and ORDER BY clauses to speed up lookups.

6. Limit Result Sets

   Use TOP (SQL Server) or LIMIT when testing queries or fetching large datasets to prevent system slowdowns.

7. Use Aliases for Clarity

   Give tables short, meaningful aliases in queries with multiple joins. It makes your code much easier to read.

8. Avoid Unnecessary Distinct

   Do not use DISTINCT unless you truly need to remove duplicates. It forces an expensive sorting operation.

9. Use EXISTS Instead of IN for Subqueries

   Use EXISTS when checking for the existence of records in large related tables. It often runs much faster than IN.

10. Format and Comment Your Code

    Use clear indentation and uppercase for keywords (SELECT, FROM, WHERE). Add comments to explain complex logic.