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testdb=# explain testdb-# select * from (testdb(# select t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.jetestdb(# from t_dwxx inner join t_grxx on t_dwxx.dwbh = t_grxx.dwbhtestdb(# inner join t_jfxx on t_grxx.grbh = t_jfxx.grbhtestdb(# where t_dwxx.dwbh IN ('1001')testdb(# union alltestdb(# select t_dwxx.dwmc,t_grxx.grbh,t_grxx.xm,t_jfxx.ny,t_jfxx.jetestdb(# from t_dwxx inner join t_grxx on t_dwxx.dwbh = t_grxx.dwbhtestdb(# inner join t_jfxx on t_grxx.grbh = t_jfxx.grbhtestdb(# where t_dwxx.dwbh IN ('1002') testdb(# ) as rettestdb-# order by ret.grbhtestdb-# limit 4; QUERY PLAN ------------------------------------------------------------------------------------------------------ Limit (cost=96.80..96.81 rows=4 width=360) -> Sort (cost=96.80..96.83 rows=14 width=360) Sort Key: t_grxx.grbh -> Append (cost=16.15..96.59 rows=14 width=360) -> Nested Loop (cost=16.15..48.19 rows=7 width=360) -> Seq Scan on t_dwxx (cost=0.00..12.00 rows=1 width=256) Filter: ((dwbh)::text = '1001'::text) -> Hash Join (cost=16.15..36.12 rows=7 width=180) Hash Cond: ((t_jfxx.grbh)::text = (t_grxx.grbh)::text) -> Seq Scan on t_jfxx (cost=0.00..17.20 rows=720 width=84) -> Hash (cost=16.12..16.12 rows=2 width=134) -> Seq Scan on t_grxx (cost=0.00..16.12 rows=2 width=134) Filter: ((dwbh)::text = '1001'::text) -> Nested Loop (cost=16.15..48.19 rows=7 width=360) -> Seq Scan on t_dwxx t_dwxx_1 (cost=0.00..12.00 rows=1 width=256) Filter: ((dwbh)::text = '1002'::text) -> Hash Join (cost=16.15..36.12 rows=7 width=180) Hash Cond: ((t_jfxx_1.grbh)::text = (t_grxx_1.grbh)::text) -> Seq Scan on t_jfxx t_jfxx_1 (cost=0.00..17.20 rows=720 width=84) -> Hash (cost=16.12..16.12 rows=2 width=134) -> Seq Scan on t_grxx t_grxx_1 (cost=0.00..16.12 rows=2 width=134) Filter: ((dwbh)::text = '1002'::text)(22 rows)
对照关系详见下图:
结合关系代数的理论和相关术语,可以更好的理解执行计划。
上一小节已通过分析日志的方式介绍了PlannedStmt的结构,这一小节结合执行计划进行对照解析,可以加深对执行计划的理解和认识。
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