Alibabacloud, Database, Query Optimization, Sql, Relational Databases.
correlated subqueries poses many challenges on execution. To compute the correlated result value (the output of the subquery), the iterative execution method is required. Take the abovementioned tpch 17 as an example. SELECT Sum(l1.extendedprice) / 7.0 AS avg_yearly FROM lineitem l1, part p WHERE