运维又背锅了？别再写慢 SQL 了！这 15 个优化技巧快收好！

Core Viewpoint - Optimizing SQL queries is essential for improving application performance, resource efficiency, and user experience in the context of exploding data volumes [1]. Index Creation - Creating indexes is crucial as they help databases quickly locate data, significantly reducing the amount of data scanned [2][7]. Query Selection - Avoid using SELECT * as it retrieves all fields from a table, wasting memory and bandwidth; instead, query only the necessary fields [3][4]. Data Return Control - Use LIMIT to control the number of rows returned, preventing excessive data retrieval [5][6]. Efficient JOIN Usage - Understanding the differences between INNER JOIN, LEFT JOIN, and RIGHT JOIN is vital to avoid performance issues; proper indexing on join columns can enhance efficiency [6][9][17]. Query Execution Plan - Utilizing the EXPLAIN command allows for analysis of how queries are executed, helping to identify issues like full table scans [18]. WHERE Clause Optimization - Optimize WHERE clauses by avoiding functions on indexed fields, which can lead to index inefficiency [19][23]. Subquery Management - Simplifying or rewriting subqueries using JOIN or Common Table Expressions (CTE) can improve performance [20][21]. DISTINCT Usage - Use DISTINCT cautiously as it can slow down queries; consider using GROUP BY or window functions for better performance [23][25]. Database-Specific Features - Leverage unique database features, such as specifying indexes or join methods, to enhance query performance [26][31]. Keeping Statistics Updated - Maintaining up-to-date statistics is crucial for the database optimizer to select the best query strategies [27]. Stored Procedures - Implementing stored procedures for common SQL operations can lead to cleaner code and improved execution efficiency [28]. ORDER BY and GROUP BY Caution - Minimize the use of ORDER BY and GROUP BY as they are resource-intensive operations; only use them when necessary [29][30]. UNION vs UNION ALL - Prefer UNION ALL over UNION when deduplication is not required, as it is faster [34][35]. Complex Query Splitting - Breaking down complex queries into simpler, intermediate queries or using materialized views can enhance readability and performance [36][38].