PARALLEL(num) -- Global level, the level of the Query Block
PARALLEL(@qbname num) -- the level of the Query Block
PARALLEL(tablename) -- the level of the Table
PARALLEL(tablename num) -- the level of the Table
NO_PARALLEL -- Global level, the level of the Query Block
NO_PARALLEL(@qbname) -- the level of the Query Block
NO_PARALLEL(tablename) -- Table level

-- Basic syntax
PQ_DISTRIBUTE(tablespec strategy1 strategy2)
PQ_DISTRIBUTE(tablespec strategy)

-- For specific operation types
PQ_DISTRIBUTE(target strategy1 strategy2)

-- Both tables undergo HASH redistribution before JOIN
SELECT /*+ PQ_DISTRIBUTE(t1 HASH, HASH) */ * 
FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

-- Outer table broadcast, inner table not redistributed
SELECT /*+ PQ_DISTRIBUTE(t1 BROADCAST, NONE) */ *
FROM small_table t1 JOIN large_table t2 ON t1.id = t2.id;

-- Perform JOIN after the table data is gathered to the Leader
SELECT /*+ PQ_DISTRIBUTE(t1 GATHER) */ *
FROM table1 t1 JOIN table2 t2 ON t1.id = t2.id;

-- Fully pushed down single-phase aggregation
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Two-phase aggregation between Worker and Leader
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE, GATHER) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Two-phase aggregation between Workers
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE NONE HASH) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Single-phase aggregation performed solely on the Leader
SELECT /*+ PQ_DISTRIBUTE(AGGREGATE GATHER) */ 
       department, AVG(salary) 
FROM employees 
GROUP BY department;

-- Partial sorting by Workers + Merge sort by the Leader
SELECT /*+ PQ_DISTRIBUTE(SORT NONE, GATHER) */ *
FROM large_table 
ORDER BY create_time DESC;

-- Global sorting performed solely on the Leader
SELECT /*+ PQ_DISTRIBUTE(SORT GATHER) */ *
FROM large_table 
ORDER BY create_time DESC;

-- Compute global ranking on the Leader node
SELECT /*+ PQ_DISTRIBUTE(WINDOW GATHER) */ 
       student_id,
       score,
       RANK() OVER (ORDER BY score DESC) as global_rank
FROM exam_scores;

-- Calculate the trend of grade changes for each student (data volume is small)
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;

-- Rankings are computed in parallel by subject partition.
SELECT /*+ PQ_DISTRIBUTE(WINDOW HASH) */ 
       subject,
       student_id,
       score,
       RANK() OVER (PARTITION BY subject ORDER BY score DESC) as subject_rank
FROM exam_scores;

-- Calculate the cumulative salary sum by department partition.
SELECT /*+ PQ_DISTRIBUTE(WINDOW HASH) */ 
       department,
       employee_id,
       salary,
       SUM(salary) OVER (PARTITION BY department ORDER BY hire_date) as cumulative_salary
FROM employees;

-- Apply the GATHER policy to specifically named windows.
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);

-- Different policies for multiple named windows
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);

-- Use HASH distribution for specific windows.
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);

-- Mixed policy: one window GATHER, another window HASH.
SELECT /*+ PQ_DISTRIBUTE(WINDOW win1 GATHER) PQ_DISTRIBUTE(WINDOW win2 HASH) */ 
       customer_id,
       order_date,
       amount,
       AVG(amount) OVER win1 as cust_avg,  -- For small data volumes, use GATHER.
       SUM(amount) OVER win2 as running_sum -- For large data volumes, use HASH.
FROM orders
WINDOW win1 AS (PARTITION BY customer_id),
       win2 AS (PARTITION BY customer_id ORDER BY order_date);