Filter 路径

Filter 步骤对单个表上的谓词求值。它接受一组行、清除其中的某些行（基于查询中提供的条件）并返回剩余行。例如，优化器可以筛选将要与其他重新分段的联接输入进行联接的联接输入的本地数据。

以下语句查询 customer_dimension 表，并使用 WHERE 子句仅筛选马萨诸塞州和新罕布什尔州的男性客户结果。

EXPLAIN SELECT
  CD.customer_name,
  CD.customer_state,
  AVG(CD.customer_age) AS avg_age,
  COUNT(*) AS count
FROM customer_dimension CD
WHERE CD.customer_state in ('MA','NH') AND CD.customer_gender = 'Male'
GROUP BY CD.customer_state, CD.customer_name;

查询计划输出如下：

 Access Path:
 +-GROUPBY HASH [Cost: 378, Rows: 544] (PATH ID: 1)
 |  Aggregates: sum_float(CD.customer_age), count(CD.customer_age), count(*)
 |  Group By: CD.customer_state, CD.customer_name
 |  Execute on: Query Initiator
 | +---> STORAGE ACCESS for CD [Cost: 372, Rows: 544] (PATH ID: 2)
 | |      Projection: public.customer_dimension_DBD_1_rep_vmartdb_design_vmartdb_design_node0001
 | |      Materialize: CD.customer_state, CD.customer_name, CD.customer_age
 | |      Filter: (CD.customer_gender = 'Male')
 | |      Filter: (CD.customer_state = ANY (ARRAY['MA', 'NH']))
 | |      Execute on: Query Initiator