select 1, (select count(*) from customer_address_001 a4 where a4.ca_address_sk = a.ca_address_sk) as GZCS from customer_address_001 a;
This SQL performance is poor. SubPlan exists in the execution plan as follows:
The core of this optimization is to eliminate subqueries. Based on the service scenario analysis, a.ca_address_sk is not null. In terms of SQL syntax, you can rewrite the SQL statement as follows:
select count(*) from customer_address_001 a4, customer_address_001 a where a4.ca_address_sk = a.ca_address_sk group by a.ca_address_sk;
To ensure that the modified statements have the same functions, not null is added to customer_address_001. ca_address_sk.