UPDATE target_table t
JOIN source_table s ON t.key = s.key
SET t.column1 = s.column2,
    t.column2 = expression(s.column3)
WHERE [condition];

UPDATE steel_company sc
JOIN (
    SELECT comp_id, SUM(capacity) AS total_capacity
    FROM steel_company_equipment
    WHERE equ_kind IN ('EAF','BOF')
    GROUP BY comp_id
) eq ON sc.comp_id = eq.comp_id
SET sc.csteel_capacity = eq.total_capacity;

UPDATE t1
JOIN t2 ON t1.id = t2.t1_id
JOIN t3 ON t2.id = t3.t2_id
SET t1.col1 = t3.col2 + 10
WHERE t3.status = 'active';

UPDATE target_table
SET column1 = (
    SELECT expression 
    FROM source_table 
    WHERE condition
    LIMIT 1
)
WHERE [condition];

-- 為高頻JOIN字段創(chuàng)建索引
ALTER TABLE steel_company ADD INDEX idx_comp_id (comp_id);
ALTER TABLE steel_company_equipment ADD INDEX idx_equ_comp (comp_id);

-- 每次處理1000條
UPDATE orders o
JOIN customers c ON o.customer_id = c.id
SET o.discount = c.vip_level * 0.1
WHERE o.status = 'pending'
LIMIT 1000;

START TRANSACTION;
-- 多次UPDATE語句
COMMIT;

EXPLAIN UPDATE orders o
JOIN customers c ON o.customer_id = c.id
SET o.discount = 0.1
WHERE c.vip_level > 3;

-- 先執(zhí)行SELECT驗證結果
SELECT t.*, s.new_value 
FROM target_table t
JOIN source_table s ON t.key = s.key
WHERE [condition];

UPDATE products p
JOIN (
    SELECT 
        product_id,
        CASE 
            WHEN stock < 10 THEN 'low'
            WHEN stock = 0 THEN 'out'
            ELSE 'normal'
        END AS stock_status
    FROM inventory
) i ON p.id = i.product_id
SET p.status = i.stock_status;

UPDATE departments d
JOIN (
    SELECT dept_id, AVG(salary) as avg_salary
    FROM employees
    GROUP BY dept_id
) e ON d.id = e.dept_id
SET d.avg_salary = e.avg_salary;

UPDATE db1.orders o
JOIN db2.customers c ON o.customer_id = c.id
SET o.discount = c.vip_discount
WHERE c.country = 'CN';