BigQuery：为什么在添加“LEFT JOIN”后我会得到更多行？

Question

WITH rawData AS (
  SELECT
    wholesaler_id,
    month,
    day,
    year,
    product_volume,
    product_gp,
    buyer_id,
    salesrep_id AS default_salesrep_id,
    salesrep_name,
    fpl
  FROM tables.transactions
  WHERE wholesaler_id = 'hos'
  AND year IN (2019, 2018)
  AND month = 12
),
salesRepsToBuyersAssociation AS (
  SELECT DISTINCT
    default_salesrep_id AS salesrep_id,
    buyer_id
  FROM rawData
)

此查询返回 60636 行：

SELECT *
FROM rawData

此查询返回 72039 行：

SELECT
  rawData.*,
  salesrep_id
FROM rawData
LEFT JOIN salesRepsToBuyersAssociation USING (buyer_id)

LEFT JOIN 假设只将匹配的salesRepsToBuyersAssociation行连接到rawData，对吗？为什么我得到的行比rawData.

Answer 1

因为salesRepsToBuyersAssociation一个或多个buyer_ids中有多行。

你可以检查这个：

select buyer_id, count(*)
from salesRepsToBuyersAssociation
group by buyer_id
having count(*) > 1;