MySQL 强制使用特定索引的操作

SELECT * FROM table_name FORCE INDEX (index_name) 
WHERE condition;

-- 强制使用名为 idx_user_id 的索引
SELECT * FROM orders FORCE INDEX (idx_user_id) 
WHERE user_id = 100 AND order_date > '2023-01-01';

SELECT * FROM table_name USE INDEX (index_name) 
WHERE condition;

-- 建议使用名为 idx_product_category 的索引
SELECT * FROM products USE INDEX (idx_product_category) 
WHERE category = 'Electronics' AND price < 1000;

SELECT * FROM table_name IGNORE INDEX (index_name) 
WHERE condition;

-- 忽略名为 idx_price 的索引
SELECT * FROM products IGNORE INDEX (idx_price) 
WHERE category = 'Electronics' AND price < 1000;

SELECT * FROM table_name USE INDEX (index1, index2) 
WHERE condition;

SELECT * FROM table1 
FORCE INDEX (index_name) 
JOIN table2 FORCE INDEX (index_name) 
ON table1.id = table2.id;

UPDATE table_name FORCE INDEX (index_name) 
SET column1 = value1 
WHERE condition;
DELETE FROM table_name FORCE INDEX (index_name) 
WHERE condition;

-- 先分析原始查询
EXPLAIN SELECT * FROM orders WHERE user_id = 100 AND status = 'completed';
-- 如果发现没有使用理想的索引，再尝试强制使用
EXPLAIN SELECT * FROM orders FORCE INDEX (idx_user_status) 
WHERE user_id = 100 AND status = 'completed';