clickhouse 中select in操作

https://clickhouse.yandex/docs/en/operations/settings/settings/

distributed_product_mode¶

Changes the behavior of distributed subqueries.

ClickHouse applies this setting when the query contains the product of distributed tables, i.e. when the query for a distributed table contains a non-GLOBAL subquery for the distributed table.

Restrictions:

• Only applied for IN and JOIN subqueries.
• Only if the FROM section uses a distributed table containing more than one shard.
• If the subquery concerns a distributed table containing more than one shard,
• Not used for a table-valued remote function.

The possible values are:

• deny — Default value. Prohibits using these types of subqueries (returns the "Double-distributed in/JOIN subqueries is denied" exception).
• local — Replaces the database and table in the subquery with local ones for the destination server (shard), leaving the normal IN / JOIN.
• global — Replaces the IN / JOIN query with GLOBAL IN / GLOBAL JOIN.
• allow — Allows the use of these types of subqueries.
• https://blog.csdn.net/ma15732625261/article/details/86607199

• 分布式子查詢

  帶有子查詢的in

  1、普通in，查詢發送到遠程服務器，且每個服務器中運行in或join子句的子查詢

  2、global in、global join時，先為global in、global join運行所有子查詢，將結果收到臨時表且將表發給每個服務器，使用臨時表運行查詢

  非分布式查詢，使用普通的in、join

  假設集群中每個服務器都存在一個正常表local_table，與分布式表distributed_table

     對distributed_table查詢，查詢被送到服務器且使用local_table運行查詢