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

• 分布式子查询

  带有子查询的in

  1、普通in，查询发送到远程服务器，且每个服务器中运行in或join子句的子查询

  2、global in、global join时，先为global in、global join运行所有子查询，将结果收到临时表且将表发给每个服务器，使用临时表运行查询

  非分布式查询，使用普通的in、join

  假设集群中每个服务器都存在一个正常表local_table，与分布式表distributed_table

     对distributed_table查询，查询被送到服务器且使用local_table运行查询