计算名称为 'count' returns 多行的列。为什么？

Question

我不明白为什么这个查询：

select count(base.*) from mytable base;

return 多行。

select count(1) from mytable base;

return正确计数。

有一列名称为 count。

谁能解释一下这种行为？

这是来自架构的信息：

table_catalog,table_schema,table_name,column_name,ordinal_position,column_default,is_nullable,data_type,character_maximum_length,character_octet_length,numeric_precision,numeric_precision_radix,numeric_scale,datetime_precision,interval_type,interval_precision,character_set_catalog,character_set_schema,character_set_name,collation_catalog,collation_schema,collation_name,domain_catalog,domain_schema,domain_name,udt_catalog,udt_schema,udt_name,scope_catalog,scope_schema,scope_name,maximum_cardinality,dtd_identifier,is_self_referencing,is_identity,identity_generation,identity_start,identity_increment,identity_maximum,identity_minimum,identity_cycle,is_generated,generation_expression,is_updatable
mydatabase,vcs,mytable,controlepunt,1,,YES,text,,1073741824,,,,,,,,,,,,,,,,mydatabase,pg_catalog,text,,,,,1,NO,NO,,,,,,,NEVER,,YES
mydatabase,vcs,mytable,norm,2,,YES,text,,1073741824,,,,,,,,,,,,,,,,mydatabase,pg_catalog,text,,,,,2,NO,NO,,,,,,,NEVER,,YES
mydatabase,vcs,mytable,fout,3,,YES,text,,1073741824,,,,,,,,,,,,,,,,mydatabase,pg_catalog,text,,,,,3,NO,NO,,,,,,,NEVER,,YES
mydatabase,vcs,mytable,count,4,,YES,bigint,,,64,2,0,,,,,,,,,,,,,mydatabase,pg_catalog,int8,,,,,4,NO,NO,,,,,,,NEVER,,YES
mydatabase,vcs,mytable,id,5,,YES,bigint,,,64,2,0,,,,,,,,,,,,,mydatabase,pg_catalog,int8,,,,,5,NO,NO,,,,,,,NEVER,,YES

Answer 1

这不是答案 - 用它来扩展 OP 的示例。它似乎与聚合函数无关：

t=# create table s91("count" int);
CREATE TABLE
Time: 38.981 ms
t=# insert into s91 values (1),(2),(3);
INSERT 0 3
Time: 13.929 ms
t=# select count(base.*) from s91 base;
 count 
-------
     1
     2
     3
(3 rows)

t=# alter table s91 rename COLUMN a to "manah_manah";
ALTER TABLE
Time: 1.025 ms
t=# select manah_manah(s91.*) from s91;
 manah_manah 
-------------
           1
           2
           3
(3 rows)

更新：似乎column(alias_name)是一个有效的语法：

s=# with c(a,b) as (values(1,2),(2,3))
select a(c),(c).a from c;
 a | a 
---+---
 1 | 1
 2 | 2
(2 rows)

Answer 2

这种风格显然被称为功能符号。

它使 table.col 和 col(table) 等价。

与table和table.*return相同的一组列。

这个问题有更多相关信息：Using functional notation in PostgreSQL queries instead of dot notation

在 postgresql 文档中：https://www.postgresql.org/docs/9.1/static/xfunc-sql.html

Another option is to use functional notation for extracting an attribute. The simple way to explain this is that we can use the notations attribute(table) and table.attribute interchangeably.

计算名称为 'count' returns 多行的列。为什么？

Count column with name 'count' returns multiple rows. Why?

sql

postgresql

count

postgresql-9.2