Basics of MySQL Query Optimization: Simple Query Speed-Up Tips for Beginners
This article explains the necessity and practical techniques of SQL query optimization, aiming to enhance system response speed and reduce user waiting time. Common mistakes for beginners include full table scans (without indexes), using SELECT * to return redundant fields, incorrect JOIN operation order, or improper use of functions. Core optimization techniques: 1. Add indexes to frequently queried fields (avoid duplicating primary key indexes and select fields with fewer duplicate values); 2. Clearly specify the required fields in SELECT to avoid redundant data; 3. Use the small table to drive the large table when performing JOINs; 4. Do not use functions on indexed fields (e.g., YEAR(create_time)); 5. Use EXPLAIN to analyze the query plan (focus on the 'type' and 'Extra' columns). Misconceptions to avoid: more indexes are not always better, OR conditions may cause index failure (replace with UNION ALL), and COUNT(DISTINCT) is inefficient. Optimization should first locate issues through EXPLAIN, prioritize mastering basic techniques, and avoid reinventing the wheel by leveraging case studies.
Read MoreIntroduction to MySQL Indexes: Why Should You Understand Indexes Even for Simple Queries?
The article explains why understanding MySQL indexes is necessary even for simple queries. An index is a special data structure (e.g., B+ tree) that maps key field values to data locations, transforming full table scans into precise positioning and significantly improving query efficiency. The reasons why even simple queries require indexes include: slow queries without indexes as data volume grows, requiring proactive planning; beginners often writing inefficient SQL (e.g., redundant conditions); and laying the foundation for complex queries (e.g., multi-table joins). Common index types include primary key, regular, unique, and composite indexes, each suited for different scenarios. Key considerations include avoiding over-indexing (e.g., on frequently updated fields) and ensuring indexes are not invalidated by using functions/expressions. The `EXPLAIN` command can verify index effectiveness. In summary, indexes are core to performance optimization; appropriate indexes should be designed based on usage scenarios to accommodate data growth and complex queries.
Read More