postgresql 在 postgres 中选择字段的数据类型

Select datatype of the field in postgres

提问by Wayne Conrad

How do I get datatype of specific field from table in postgres ? For example I have the following table, student_details ( stu_id integer, stu_name varchar(30 ), joined_date timestamp );

如何从 postgres 的表中获取特定字段的数据类型？例如我有下表， student_details ( stu_id integer, stu_name varchar(30 ), connected_date timestamp );

In this using the field name / or any other way, I need to get the datatype of the specific field. Is there any possibility ?

在此使用字段名称 / 或任何其他方式，我需要获取特定字段的数据类型。有没有可能？

回答by Wayne Conrad

You can get data types from the information_schema(8.4 docs referenced here, but this is not a new feature):

您可以从information_schema 中获取数据类型（此处引用了 8.4 文档，但这不是新功能）：

=# select column_name, data_type from information_schema.columns
-# where table_name = 'config';
    column_name     | data_type 
--------------------+-----------
 id                 | integer
 default_printer_id | integer
 master_host_enable | boolean
(3 rows)

回答by Nathan Villaescusa

You can use the pg_typeof()function, which also works well for arbitrary values.

您可以使用pg_typeof()函数，该函数也适用于任意值。

SELECT pg_typeof("stu_id"), pg_typeof(100) from student_details limit 1;

回答by Romulo Freires

Try this request :

试试这个请求：

SELECT column_name, data_type FROM information_schema.columns WHERE 
table_name = 'YOUR_TABLE' AND column_name = 'YOUR_FIELD';

回答by Romulo Freires

run psql -Eand then \d student_details

运行psql -E然后\d student_details

回答by Fil

If you like 'Mike Sherrill' solution but don't want to use psql, I used this query to get the missing information:

如果您喜欢 'Mike Sherrill' 解决方案但不想使用 psql，我使用此查询来获取丢失的信息：

select column_name,
case 
    when domain_name is not null then domain_name
    when data_type='character varying' THEN 'varchar('||character_maximum_length||')'
    when data_type='numeric' THEN 'numeric('||numeric_precision||','||numeric_scale||')'
    else data_type
end as myType
from information_schema.columns
where table_name='test'

with result:

结果：

column_name |     myType
-------------+-------------------
 test_id     | test_domain
 test_vc     | varchar(15)
 test_n      | numeric(15,3)
 big_n       | bigint
 ip_addr     | inet

回答by Mike Sherrill 'Cat Recall'

The information schema views and pg_typeof() return incomplete type information. Of these answers, psqlgives the most precise type information. (The OP might not need such precise information, but should know the limitations.)

信息模式视图和 pg_typeof() 返回不完整的类型信息。在这些答案中，psql给出了最精确的类型信息。（OP 可能不需要如此精确的信息，但应该知道这些限制。）

create domain test_domain as varchar(15);

create table test (
  test_id test_domain, 
  test_vc varchar(15), 
  test_n numeric(15, 3), 
  big_n bigint,
  ip_addr inet
);

Using psqland \d public.testcorrectly shows the use of the data type test_domain, the length of varchar(n) columns, and the precision and scale of numeric(p, s) columns.

使用psql并\d public.test正确显示数据类型的使用、test_domainvarchar(n) 列的长度以及 numeric(p, s) 列的精度和小数位数。

sandbox=# \d public.test
             Table "public.test"
 Column  |         Type          | Modifiers
---------+-----------------------+-----------
 test_id | test_domain           |
 test_vc | character varying(15) |
 test_n  | numeric(15,3)         |
 big_n   | bigint                |
 ip_addr | inet                  |

This query against an information_schema view does notshow the use of test_domainat all. It also doesn't report the details of varchar(n) and numeric(p, s) columns.

这个针对 information_schema 视图的查询根本没有显示使用test_domain。它也不报告 varchar(n) 和 numeric(p, s) 列的详细信息。

select column_name, data_type 
from information_schema.columns 
where table_catalog = 'sandbox'
  and table_schema = 'public'
  and table_name = 'test';

 column_name |     data_type
-------------+-------------------
 test_id     | character varying
 test_vc     | character varying
 test_n      | numeric
 big_n       | bigint
 ip_addr     | inet

You mightbe able to get all that information by joining other information_schema views, or by querying the system tables directly. psql -Emight help with that.

您可以通过加入其他 information_schema 视图或直接查询系统表来获取所有这些信息。psql -E可能会有所帮助。

The function pg_typeof()correctly shows the use of test_domain, but doesn't report the details of varchar(n) and numeric(p, s) columns.

该函数pg_typeof()正确显示了 的使用test_domain，但不报告 varchar(n) 和 numeric(p, s) 列的详细信息。

select pg_typeof(test_id) as test_id, 
       pg_typeof(test_vc) as test_vc,
       pg_typeof(test_n) as test_n,
       pg_typeof(big_n) as big_n,
       pg_typeof(ip_addr) as ip_addr
from test;

   test_id   |      test_vc      | test_n  | big_n  | ip_addr
-------------+-------------------+---------+--------+---------
 test_domain | character varying | numeric | bigint | inet

回答by Piotr Findeisen

Pulling data type from information_schemais possible, but not convenient (requires joining several columns with a casestatement). Alternatively one can use format_typebuilt-in function to do that, but it works on internal type identifiers that are visible in pg_attributebut not in information_schema. Example

从中提取数据类型information_schema是可能的，但不方便（需要使用case语句连接多个列）。或者，可以使用format_type内置函数来做到这一点，但它适用于pg_attribute在information_schema. 例子

SELECT a.attname as column_name, format_type(a.atttypid, a.atttypmod) AS data_type
FROM pg_attribute a JOIN pg_class b ON a.attrelid = b.relfilenode
WHERE a.attnum > 0 -- hide internal columns
AND NOT a.attisdropped -- hide deleted columns
AND b.oid = 'my_table'::regclass::oid; -- example way to find pg_class entry for a table

Based on https://gis.stackexchange.com/a/97834.

基于https://gis.stackexchange.com/a/97834。