【笔记】开发指南—SQL调优指南—SQL调优进阶—子查询优化和执行

/* 例子：非关联子查询 */
SELECT * FROM lineitem WHERE l_partkey IN (SELECT p_partkey FROM part);
/* 例子：关联子查询（l_suppkey 是关联项） */
SELECT * FROM lineitem WHERE l_partkey IN (SELECT ps_partkey FROM partsupp WHERE ps_suppkey = l_suppkey);

> EXPLAIN SELECT p_partkey, (
      SELECT COUNT(ps_partkey) FROM partsupp WHERE ps_suppkey = p_partkey
      ) supplier_count FROM part;
Project(p_partkey="p_partkey", supplier_count="CASE(IS NULL($10), 0, $9)", cor=[$cor0])
  HashJoin(condition="p_partkey = ps_suppkey", type="left")
    Gather(concurrent=true)
      LogicalView(tables="part_[0-7]", shardCount=8, sql="SELECT * FROM `part` AS `part`")
    Project(count(ps_partkey)="count(ps_partkey)", ps_suppkey="ps_suppkey", count(ps_partkey)2="count(ps_partkey)")
      HashAgg(group="ps_suppkey", count(ps_partkey)="SUM(count(ps_partkey))")
        Gather(concurrent=true)
          LogicalView(tables="partsupp_[0-7]", shardCount=8, sql="SELECT `ps_suppkey`, COUNT(`ps_partkey`) AS `count(ps_partkey)` FROM `partsupp` AS `partsupp` GROUP BY `ps_suppkey`")

> EXPLAIN SELECT p_partkey, (

> EXPLAIN SELECT * FROM lineitem WHERE l_partkey IN (SELECT ps_partkey FROM partsupp WHERE ps_suppkey = l_suppkey) OR l_partkey IS NOT
Filter(condition="IS(in,[$1])[29612489] OR l_partkey < ?0")
  Gather(concurrent=true)
    LogicalView(tables="QIMU_0000_GROUP,QIMU_0001_GROUP.lineitem_[0-7]", shardCount=8, sql="SELECT * FROM `lineitem` AS `lineitem`")
>> individual correlate subquery : 29612489
Gather(concurrent=true)
  LogicalView(tables="QIMU_0000_GROUP,QIMU_0001_GROUP.partsupp_[0-7]", shardCount=8, sql="SELECT * FROM (SELECT `ps_partkey` FROM `partsupp` AS `partsupp` WHERE (`ps_suppkey` = `l_suppkey`)) AS `t0` WHERE (((`l_partkey` = `ps_partkey`) OR (`l_partkey` IS NULL)) OR (`ps_partkey` IS NULL))")