公用表表达式（CTE）

BigQuery 入门

Matthew Forrest

Field CTO

什么是 CTE？

-- WITH 关键字开始 CTE
WITH our_cte AS (
  SELECT column1, column2
  FROM table
)


/* CTE 放在括号中，可在下面的主查询中当作表使用 */
SELECT *
FROM our_cte

子查询 vs. CTE

子查询

SELECT *
FROM (
  SELECT order_id, status
  FROM ecommerce.ecomm_order_status
) AS subquery

CTE

WITH cte_name AS (
  SELECT order_id, status
  FROM ecommerce.ecomm_order_status
)
SELECT *
FROM cte_name

编写 CTE

-- 所有 CTE 都以 WITH 开头
WITH cte_name AS


-- CTE 放在括号中
(SELECT col_1, col_2
 FROM tablename WHERE col_1 > 10
)


-- 新的 CTE 'cte_name' 仅在本查询范围内可用

SELECT * FROM cte_name LIMIT 10

使用多个 CTE

WITH orders AS (
  SELECT order_id, status
  FROM ecommerce.ecomm_order_status
),

-- 其他 CTE 不再使用 WITH，使用逗号分隔
order_details AS (
SELECT orders.*, details.order_items
FROM ecommerce.ecomm_orders details 
```

用 CTE 筛选数据

WITH filtered_data AS (
  SELECT *
  FROM ecommerce.ecomm_orders
  -- 在 CTE 中筛选数据
  WHERE order_status = 'delivered'
)
SELECT order_id, order_status
FROM filtered_data

| order_id | order_status |
|----------|--------------|
| 1        | delivered    |
| 2        | delivered    |

用 CTE 优化查询

WITH precomputed_data AS (
  SELECT order_id, SUM(payment_value) AS total
  FROM ecommerce.ecomm_payments
  GROUP BY order_id
)
SELECT *
FROM precomputed_data
WHERE total > 1000

| order_id | total   |
|----------|---------|
| 1        | 50000   |
| 2        | 8000    |

用 CTE 连接数据

WITH cte1 AS (
  SELECT order_id, status
  FROM ecommerce.ecomm_order_status
),
cte2 AS (
  SELECT order_id, order_items
  FROM ecommerce.ecomm_orders
)
SELECT *
FROM cte1
JOIN cte2 USING (order_id)

Passons à la pratique !

BigQuery 入门