本篇内容主要讲解“Oracle与PostgreSQL子查询有什么不同”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Oracle与PostgreSQL子查询有什么不同”吧!
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准确的表达应该是在子查询的having条件中出现agg函数且依赖父查询的相关字段时，Oracle支持而PG不支持。
Oracle
创建表，插入数据，执行查询，OK！
TEST-orcl@DESKTOP-V430TU3>drop table tbl1; Table dropped. TEST-orcl@DESKTOP-V430TU3>drop table tbl2; Table dropped. TEST-orcl@DESKTOP-V430TU3>drop table tbl3; Table dropped. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>create table tbl1 (id int,c1 int,c2 int,c3 int); Table created. TEST-orcl@DESKTOP-V430TU3>create table tbl2 (id int,c1 int,c2 int,c3 int); Table created. TEST-orcl@DESKTOP-V430TU3>create table tbl3 (id int,c1 int,c2 int,c3 int); Table created. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(2,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(2,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl1 values(3,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(2,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(2,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl2 values(3,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>truncate table tbl3; Table truncated. TEST-orcl@DESKTOP-V430TU3>insert into tbl3 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3>insert into tbl3 values(1,1,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>commit; Commit complete. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>truncate table tbl3; Table truncated. TEST-orcl@DESKTOP-V430TU3>insert into tbl3 values(1,2,1,1); 1 row created. TEST-orcl@DESKTOP-V430TU3> TEST-orcl@DESKTOP-V430TU3>select a.id,sum(a.c1) as sum_c1,sum(a.c2) as sum_c2 2 from tbl1 a,tbl2 b 3 where a.id = b.id 4 and exists (select 1 from tbl3 c where c.id = a.id group by c.id having sum(c.c1) > sum(a.c1)) 5 group by a.id; ID SUM_C1 SUM_C2 ---------- ---------- ---------- 1 9 9 TEST-orcl@DESKTOP-V430TU3
不过，就算Oracle支持这样的写法，也不建议这样来写，原因是SQL语义理解起来并不友好，难以理解。
PG
创建表，插入数据，执行查询，出错。
[pg12@localhost ~]$ psql Expanded display is used automatically. psql (12.1) Type "help" for help. [local:/data/run/pg12]:5120 pg12@testdb=# drop table tbl1; s(1,1,1,1); insert into tbl1 values(1,1,1,1); insert into tbl2 select * from tbl1; insert into tbl2 select * from tbl1; insert into tbl3 select * from tbl1; commit; ERROR: table "tbl1" does not exist [local:/data/run/pg12]:5120 pg12@testdb=# drop table tbl2; ERROR: table "tbl2" does not exist [local:/data/run/pg12]:5120 pg12@testdb=# drop table tbl3; ERROR: table "tbl3" does not exist [local:/data/run/pg12]:5120 pg12@testdb=# [local:/data/run/pg12]:5120 pg12@testdb=# create table tbl1 (id int,c1 int,c2 int,c3 int); CREATE TABLE [local:/data/run/pg12]:5120 pg12@testdb=# create table tbl2 (id int,c1 int,c2 int,c3 int); CREATE TABLE [local:/data/run/pg12]:5120 pg12@testdb=# create table tbl3 (id int,c1 int,c2 int,c3 int); CREATE TABLE [local:/data/run/pg12]:5120 pg12@testdb=# [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl1 values(1,1,1,1); INSERT 0 1 [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl1 values(1,1,1,1); INSERT 0 1 [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl1 values(1,1,1,1); INSERT 0 1 [local:/data/run/pg12]:5120 pg12@testdb=# [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl2 select * from tbl1; INSERT 0 3 [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl2 select * from tbl1; INSERT 0 3 [local:/data/run/pg12]:5120 pg12@testdb=# [local:/data/run/pg12]:5120 pg12@testdb=# insert into tbl3 select * from tbl1; INSERT 0 3 [local:/data/run/pg12]:5120 pg12@testdb=# [local:/data/run/pg12]:5120 pg12@testdb=# commit; WARNING: there is no transaction in progress COMMIT [local:/data/run/pg12]:5120 pg12@testdb=# select a.id,sum(a.c1) as sum_c1,sum(a.c2) as sum_c2 pg12@testdb-# from tbl1 a,tbl2 b pg12@testdb-# where a.id = b.id pg12@testdb-# and exists (select 1 from tbl3 c where c.id = a.id group by c.id having sum(c.c1) = sum(a.c1)) pg12@testdb-# group by a.id; ERROR: aggregate functions are not allowed in WHERE LINE 4: ...ere c.id = a.id group by c.id having sum(c.c1) = sum(a.c1)) ^ [local:/data/run/pg12]:5120 pg12@testdb=#
出现的错误是“aggregate functions are not allowed in WHERE”，但条件明明在having怎么报WHERE中出现agg函数呢？原因是PG认为条件sum(c.c1) = sum(a.c1)中的a.c1出现在父查询中，该条件认为是WHERE中的条件。
到此，相信大家对“Oracle与PostgreSQL子查询有什么不同”有了更深的了解，不妨来实际操作一番吧！这里是创新互联网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！