pg_tables提供了一个表列表。是否有pg_columns或其等价物来提供列列表？
在DB2中，我将查询sysibm.systables / columns以获取此类信息。红移中的等价物是什么？
答案 0 :(得分：18)
使用PG_TABLE_DEF表获取该信息：
看起来像这样：
select * from pg_table_def where tablename = 't2';
schemaname|tablename|column| type | encoding | distkey |sortkey| notnull ----------+---------+------+---------+----------+---------+-------+--------- public | t2 | c1 | bigint | none | t | 0 | f public | t2 | c2 | integer | mostly16 | f | 0 | f public | t2 | c3 | integer | none | f | 1 | t public | t2 | c4 | integer | none | f | 2 | f (4 rows)
答案 1 :(得分：8)
information_schema是一个非常重要的模式，是ANSI标准的一部分，但并不是那么标准。如果所有关系数据库都支持它会很好，但它们并非都有 - MySQL 5，SQL Server（2000+）和PostgreSQL（7.4+）支持它们。 Oracle和DB2显然仍然没有，但有希望。对于支持information_schema的DBMS，有不同的级别，但总的来说，您可以非常放心地查找具有相同命名字段的表，视图，列，其中包含数据库中所有表的完整列表，视图列表和查看定义DDL以及所有列，列大小和数据类型。
pg_catalog架构是标准的PostgreSQL元数据和核心架构。您将在此处找到预定义的全局postgres函数以及有关您的数据库的有用元数据，这些数据非常特定于postgres。这是postgres用于内部管理事物的模式。许多信息与information_schema中的信息重叠，但是对于information_schema中存在的数据，information_schema更容易查询，并且需要更少或没有连接来获得基本信息。
因此，对于基本查询，您最好使用information_schema。
此页面（http://www.alberton.info/postgresql_meta_info.html）显示了一个很好的查询列表，以获取有关架构的信息。以下是与此问题相关的内容：
SELECT a.attname
FROM pg_class c, pg_attribute a, pg_type t
WHERE c.relname = 'test2'
AND a.attnum > 0
AND a.attrelid = c.oid
AND a.atttypid = t.oid
-- with INFORMATION_SCHEMA:
SELECT column_name
FROM information_schema.columns
WHERE table_name = 'test2';
有关详细信息，请：
SELECT a.attnum AS ordinal_position,
a.attname AS column_name,
t.typname AS data_type,
a.attlen AS character_maximum_length,
a.atttypmod AS modifier,
a.attnotnull AS notnull,
a.atthasdef AS hasdefault
FROM pg_class c,
pg_attribute a,
pg_type t
WHERE c.relname = 'test2'
AND a.attnum > 0
AND a.attrelid = c.oid
AND a.atttypid = t.oid
ORDER BY a.attnum;
-- with INFORMATION_SCHEMA:
SELECT ordinal_position,
column_name,
data_type,
column_default,
is_nullable,
character_maximum_length,
numeric_precision
FROM information_schema.columns
WHERE table_name = 'test2'
ORDER BY ordinal_position;
答案 2 :(得分：4)
Pg_table_def可以提供一些有用的信息，但它不会告诉您列顺序，默认或字符字段大小。这是一个可以向您显示所有内容的查询（请注意，自原始帖子以来我已更新此查询，现在它包括列编码，diststyle / distkey，sortkey和主键以及打印出显示表所有者的语句）：
select pk.pkey, tm.schemaname||'.'||tm.tablename, 'create table '||tm.schemaname||'.'||tm.tablename
||' ('
||cp.coldef
-- primary key
||decode(pk.pkey,null,'',pk.pkey)
-- diststyle and dist key
||decode(d.distkey,null,') diststyle '||dist_style||' ',d.distkey)
--sort key
|| (select decode(skey,null,'',skey) from (select
' sortkey(' ||substr(array_to_string(
array( select ','||cast(column_name as varchar(100)) as str from
(select column_name from information_schema.columns col where col.table_schema= tm.schemaname and col.table_name=tm.tablename) c2
join
(-- gives sort cols
select attrelid as tableid, attname as colname, attsortkeyord as sort_col_order from pg_attribute pa where
pa.attnum > 0 AND NOT pa.attisdropped AND pa.attsortkeyord > 0
) st on tm.tableid=st.tableid and c2.column_name=st.colname order by sort_col_order
)
,'')
,2,10000) || ')' as skey
))
||';'
-- additional alter table queries here to set owner
|| 'alter table '||tm.schemaname||'.'||tm.tablename||' owner to "'||tm.owner||'";'
from
-- t master table list
(
SELECT substring(n.nspname,1,100) as schemaname, substring(c.relname,1,100) as tablename, c.oid as tableid ,use2.usename as owner, decode(c.reldiststyle,0,'EVEN',1,'KEY',8,'ALL') as dist_style
FROM pg_namespace n, pg_class c, pg_user use2
WHERE n.oid = c.relnamespace
AND nspname NOT IN ('pg_catalog', 'pg_toast', 'information_schema')
AND c.relname <> 'temp_staging_tables_1'
and c.relowner = use2.usesysid
) tm
-- cp creates the col params for the create string
join
(select
substr(str,(charindex('QQQ',str)+3),(charindex('ZZZ',str))-(charindex('QQQ',str)+3)) as tableid
,substr(replace(replace(str,'ZZZ',''),'QQQ'||substr(str,(charindex('QQQ',str)+3),(charindex('ZZZ',str))-(charindex('QQQ',str)+3)),''),2,10000) as coldef
from
( select array_to_string(array(
SELECT 'QQQ'||cast(t.tableid as varchar(10))||'ZZZ'|| ','||column_name||' '|| decode(udt_name,'bpchar','char',udt_name) || decode(character_maximum_length,null,'', '('||cast(character_maximum_length as varchar(9))||')' )
-- default
|| decode(substr(column_default,2,8),'identity','',null,'',' default '||column_default||' ')
-- nullable
|| decode(is_nullable,'YES',' NULL ','NO',' NOT NULL ')
-- identity
|| decode(substr(column_default,2,8),'identity',' identity('||substr(column_default,(charindex('''',column_default)+1), (length(column_default)-charindex('''',reverse(column_default))-charindex('''',column_default) ) ) ||') ', '')
-- encoding
|| decode(enc,'none','',' encode '||enc)
as str
from
-- ci all the col info
(
select cast(t.tableid as int), cast(table_schema as varchar(100)), cast(table_name as varchar(100)), cast(column_name as varchar(100)),
cast(ordinal_position as int), cast(column_default as varchar(100)), cast(is_nullable as varchar(20)) , cast(udt_name as varchar(50)) ,cast(character_maximum_length as int),
sort_col_order , decode(d.colname,null,0,1) dist_key , e.enc
from
(select * from information_schema.columns c where c.table_schema= t.schemaname and c.table_name=t.tablename) c
left join
(-- gives sort cols
select attrelid as tableid, attname as colname, attsortkeyord as sort_col_order from pg_attribute a where
a.attnum > 0 AND NOT a.attisdropped AND a.attsortkeyord > 0
) s on t.tableid=s.tableid and c.column_name=s.colname
left join
(-- gives encoding
select attrelid as tableid, attname as colname, format_encoding(a.attencodingtype::integer) AS enc from pg_attribute a where
a.attnum > 0 AND NOT a.attisdropped
) e on t.tableid=e.tableid and c.column_name=e.colname
left join
-- gives dist col
(select attrelid as tableid, attname as colname from pg_attribute a where
a.attnum > 0 AND NOT a.attisdropped AND a.attisdistkey = 't'
) d on t.tableid=d.tableid and c.column_name=d.colname
order by ordinal_position
) ci
-- for the working array funct
), '') as str
from
(-- need tableid
SELECT substring(n.nspname,1,100) as schemaname, substring(c.relname,1,100) as tablename, c.oid as tableid
FROM pg_namespace n, pg_class c
WHERE n.oid = c.relnamespace
AND nspname NOT IN ('pg_catalog', 'pg_toast', 'information_schema')
) t
)) cp on tm.tableid=cp.tableid
-- primary key query here
left join
(select c.oid as tableid, ', primary key '|| substring(pg_get_indexdef(indexrelid),charindex('(',pg_get_indexdef(indexrelid))-1 ,60) as pkey
from pg_index i , pg_namespace n, pg_class c
where i.indisprimary=true
and i.indrelid =c.oid
and n.oid = c.relnamespace
) pk on tm.tableid=pk.tableid
-- dist key
left join
( select
-- close off the col defs after the primary key
')' ||
' distkey('|| cast(column_name as varchar(100)) ||')' as distkey, t.tableid
from information_schema.columns c
join
(-- need tableid
SELECT substring(n.nspname,1,100) as schemaname, substring(c.relname,1,100) as tablename, c.oid as tableid
FROM pg_namespace n, pg_class c
WHERE n.oid = c.relnamespace
AND nspname NOT IN ('pg_catalog', 'pg_toast', 'information_schema')
) t on c.table_schema= t.schemaname and c.table_name=t.tablename
join
-- gives dist col
(select attrelid as tableid, attname as colname from pg_attribute a where
a.attnum > 0 AND NOT a.attisdropped AND a.attisdistkey = 't'
) d on t.tableid=d.tableid and c.column_name=d.colname
) d on tm.tableid=d.tableid
where tm.schemaname||'.'||tm.tablename='myschema.mytable'