SetOp

算子说明

SetOp算子用于将两个或多个查询结果合并成一个结果集。SetOp算子包括INTERSECT和EXCEPT。

典型场景

• INTERSECT：返回两个查询结果的交集，即两个结果集中都存在的行。
• INTERSECT ALL：返回两个查询结果的交集，包括重复的行。
• EXCEPT：返回第一个查询结果中存在，但第二个查询结果中不存在的行。
• EXCEPT ALL：返回第一个查询结果中存在，但第二个查询结果中不存在的行，包括重复的行。

示例

示例1：INTERSECT。

--数据准备 
gaussdb=# DROP TABLE IF EXISTS t;
gaussdb=# CREATE TABLE t(a int, b int, c int); 
CREATE TABLE 
gaussdb=# INSERT INTO t VALUES(generate_series(1, 10), generate_series(601, 610), generate_series(901, 910)); 
INSERT 0 10

--执行结果。 
gaussdb=# EXPLAIN SELECT * FROM t INTERSECT SELECT * FROM t; 
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Streaming (type: GATHER)  (cost=27.94..28.61 rows=21 width=12)
   Node/s: All datanodes
   ->  SetOp Intersect  (cost=27.13..27.39 rows=21 width=12)
         ->  Sort  (cost=27.13..27.20 rows=42 width=12)
               Sort Key: "*SELECT* 1".a, "*SELECT* 1".b, "*SELECT* 1".c
               ->  Append  (cost=0.00..26.52 rows=42 width=12)
                     ->  Subquery Scan on "*SELECT* 1"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
                     ->  Subquery Scan on "*SELECT* 2"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
(10 rows)

上述示例中，SetOp算子输出信息如下所示。

示例2：INTERSECT ALL。

gaussdb=# EXPLAIN SELECT * FROM t INTERSECT ALL SELECT * FROM t; 
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Streaming (type: GATHER)  (cost=27.94..28.61 rows=21 width=12)
   Node/s: All datanodes
   ->  SetOp Intersect All  (cost=27.13..27.39 rows=21 width=12)
         ->  Sort  (cost=27.13..27.20 rows=42 width=12)
               Sort Key: "*SELECT* 1".a, "*SELECT* 1".b, "*SELECT* 1".c
               ->  Append  (cost=0.00..26.52 rows=42 width=12)
                     ->  Subquery Scan on "*SELECT* 1"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
                     ->  Subquery Scan on "*SELECT* 2"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
(10 rows)

上述示例中，SetOp算子输出信息如下所示。

示例3：EXCEPT。

 
gaussdb=# EXPLAIN SELECT * FROM t EXCEPT SELECT * FROM t; 
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Streaming (type: GATHER)  (cost=27.94..28.61 rows=21 width=12)
   Node/s: All datanodes
   ->  SetOp Except  (cost=27.13..27.39 rows=21 width=12)
         ->  Sort  (cost=27.13..27.20 rows=42 width=12)
               Sort Key: "*SELECT* 1".a, "*SELECT* 1".b, "*SELECT* 1".c
               ->  Append  (cost=0.00..26.52 rows=42 width=12)
                     ->  Subquery Scan on "*SELECT* 1"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
                     ->  Subquery Scan on "*SELECT* 2"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
(10 rows)

上述示例中，SetOp算子输出信息如下所示。

示例4：EXCEPT ALL。

gaussdb=# EXPLAIN SELECT * FROM t EXCEPT ALL SELECT * FROM t; 
                                         QUERY PLAN
--------------------------------------------------------------------------------------------
 Streaming (type: GATHER)  (cost=27.94..28.61 rows=21 width=12)
   Node/s: All datanodes
   ->  SetOp Except All  (cost=27.13..27.39 rows=21 width=12)
         ->  Sort  (cost=27.13..27.20 rows=42 width=12)
               Sort Key: "*SELECT* 1".a, "*SELECT* 1".b, "*SELECT* 1".c
               ->  Append  (cost=0.00..26.52 rows=42 width=12)
                     ->  Subquery Scan on "*SELECT* 1"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
                     ->  Subquery Scan on "*SELECT* 2"  (cost=0.00..13.26 rows=21 width=12)
                           ->  Seq Scan on t  (cost=0.00..13.13 rows=20 width=12)
(10 rows)

--删除。
gaussdb=# DROP TABLE t;

上述示例中，SetOp算子输出信息如下所示。