PARALLEL(num) -- Global级、Query Block级
PARALLEL(@qbname num) -- Query Block级
PARALLEL(tablename) -- Table 级
PARALLEL(tablename num) -- Table 级
NO_PARALLEL -- Global级、Query Block级
NO_PARALLEL(@qbname) -- Query Block级
NO_PARALLEL(tablename) -- Table 级

-- 基本语法
PQ_DISTRIBUTE(tablespec strategy1 strategy2)
PQ_DISTRIBUTE(tablespec strategy)

-- 针对特定操作类型
PQ_DISTRIBUTE(target strategy1 strategy2)

-- 两个表都进行 HASH 重分布后 JOIN
SELECT /*+ PQ_DISTRIBUTE(t1 HASH, HASH) */ * 
FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

-- 外表广播，内表不重分布
SELECT /*+ PQ_DISTRIBUTE(t1 BROADCAST, NONE) */ *
FROM small_table t1 JOIN large_table t2 ON t1.id = t2.id;

-- 表数据收集到 Leader 后执行 JOIN
SELECT /*+ PQ_DISTRIBUTE(t1 GATHER) */ *
FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

-- 完全下推的一阶段聚合
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Worker 和 Leader 二阶段聚合
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE, GATHER) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Worker 和 Worker 二阶段聚合
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE HASH) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- 只在 Leader 上执行的一阶段聚合
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE GATHER) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Worker 局部排序 + Leader 归并排序
SELECT /*+ PQ_DISTRIBUTE(SORT NONE, GATHER) */ *
FROM large_table 
ORDER BY create_time DESC;

-- 只在 Leader 上全局排序
SELECT /*+ PQ_DISTRIBUTE(SORT GATHER) */ *
FROM large_table 
ORDER BY create_time DESC;

-- 在 Leader 节点上计算全局排名
SELECT /*+ PQ_DISTRIBUTE(WINDOW GATHER) */ 
       student_id,
       score,
       RANK() OVER (ORDER BY score DESC) as global_rank
FROM exam_scores;

-- 计算每个学生的成绩变化趋势（数据量较小）
SELECT /*+ PQ_DISTRIBUTE(WINDOW GATHER) */ 
       student_id,
       exam_date,
       score,
       LAG(score) OVER (PARTITION BY student_id ORDER BY exam_date) as prev_score
FROM student_scores;

-- 按学科分区并行计算排名
SELECT /*+ PQ_DISTRIBUTE(WINDOW HASH) */ 
       subject,
       student_id,
       score,
       RANK() OVER (PARTITION BY subject ORDER BY score DESC) as subject_rank
FROM exam_scores;

-- 按部门分区计算工资累计总和
SELECT /*+ PQ_DISTRIBUTE(WINDOW HASH) */ 
       department,
       employee_id,
       salary,
       SUM(salary) OVER (PARTITION BY department ORDER BY hire_date) as cumulative_salary
FROM employees;

-- 为特定命名的窗口使用GATHER策略
SELECT /*+ PQ_DISTRIBUTE(WINDOW win1 GATHER) */ 
       student_id,
       subject,
       score,
       AVG(score) OVER win1 as avg_score,
       RANK() OVER (PARTITION BY subject ORDER BY score DESC) as rank
FROM exam_scores
WINDOW win1 AS (PARTITION BY student_id);

-- 多个命名窗口的不同策略
SELECT /*+ PQ_DISTRIBUTE(WINDOW win1 GATHER) PQ_DISTRIBUTE(WINDOW win2 HASH) */ 
       department,
       employee_id,
       salary,
       AVG(salary) OVER win1 as dept_avg,
       SUM(salary) OVER win2 as running_total
FROM employees
WINDOW win1 AS (PARTITION BY department),
       win2 AS (PARTITION BY department ORDER BY hire_date);

-- 为特定窗口使用 HASH 分布
SELECT /*+ PQ_DISTRIBUTE(WINDOW win1 HASH) */ 
       product_category,
       product_id,
       sales_amount,
       SUM(sales_amount) OVER win1 as category_total,
       RANK() OVER (ORDER BY sales_amount DESC) as global_rank
FROM sales_data
WINDOW win1 AS (PARTITION BY product_category);

-- 混合策略：一个窗口 GATHER，另一个窗口 HASH
SELECT /*+ PQ_DISTRIBUTE(WINDOW win1 GATHER) PQ_DISTRIBUTE(WINDOW win2 HASH) */ 
       customer_id,
       order_date,
       amount,
       AVG(amount) OVER win1 as cust_avg,  -- 小数据量用GATHER
       SUM(amount) OVER win2 as running_sum -- 大数据量用HASH
FROM orders
WINDOW win1 AS (PARTITION BY customer_id),
       win2 AS (PARTITION BY customer_id ORDER BY order_date);