在Redshift中获取表模式

Question

你好，我正在尝试获取现有表的模式。我是MySQL开发人员，现在正在尝试使用Amazon Redshift。如何导出现有表的模式？在MySQL中，我们可以使用show create table命令。

SHOW CREATE TABLE tblName;

- user3277217

---

现在在Redshift中可以使用show table {table_name}命令了。 - Tyler

Answer 1

最近我编写了一个Python脚本，用于在Redshift集群之间克隆表模式。如果您只需要表的列和列类型，则可以通过以下方式实现：

select column_name,
  case
    when data_type = 'integer' then 'integer'
    when data_type = 'bigint' then 'bigint'
    when data_type = 'smallint' then 'smallint'
    when data_type = 'text' then 'text'
    when data_type = 'date' then 'date'
    when data_type = 'real' then 'real'
    when data_type = 'boolean' then 'boolean'
    when data_type = 'double precision' then 'float8'
    when data_type = 'timestamp without time zone' then 'timestamp'
    when data_type = 'character' then 'char('||character_maximum_length||')'
    when data_type = 'character varying' then 'varchar('||character_maximum_length||')'
    when data_type = 'numeric' then 'numeric('||numeric_precision||','||numeric_scale||')'
    else 'unknown'
  end as data_type,
  is_nullable,
  column_default
 from information_schema.columns
 where table_schema = 'xxx' and table_name = 'xxx' order by ordinal_position
;

但如果你需要压缩类型和分布键/排序键，你需要查询另一张表：

select * from pg_table_def where tablename = 'xxx' and schemaname='xxx';

- ciphor

Answer 2

这个查询将提供完整的模式定义，包括Redshift特定属性分布类型/键、排序键、主键和列编码的创建语句形式，并提供一个alter表语句，将所有者设为当前所有者。唯一不能告诉您的是外键。我正在处理后者，但在RS中存在当前权限问题，无法查询正确的表。这个查询可能需要一些调整，但我没有时间或需要进一步工作。

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'

- mike_pdb

---

AWS发布了一个非常实用的工具，https://github.com/awslabs/amazon-redshift-utils，可用于迁移至正确的压缩编码。它包含了AWS用于描述表结构的所有查询，唯一的例外是授权（有关该组件，请参阅https://dev59.com/4GMl5IYBdhLWcg3wCDKW#21178589）。 - mike_pdb

Answer 3

如果您想使用创建语句、约束和触发器获取表结构，可以使用pg_dump实用程序。

pg_dump -U user_name -s -t table_name -d db_name
Note: -s used for schema only dump
if you want to take the data only dump , you can use -a switch.

这将输出带有所有约束条件的创建语法。希望这能帮到你。

- Anant

---

看起来对于Postgres 7.3+，pg_dump中的-d标志已经消失了，而数据库是一个常规的命令行参数。也就是说：pg_dump -U user_name -s -t table_name db_name。 - congusbongus

pg_dump 不会包含有关 sortkeys、distkeys、diststyle 或列编码的任何信息 - nico

Answer 4

我没有找到任何完整的解决方案。于是我编写了一个Python脚本：https://github.com/cxmcc/redshift_show_create_table。它可以像pg_dump一样工作，并处理基本的Redshift特性，如SORTKEY / DISTKEY / DISTSTYLES等。

- user4766167

Answer 5

针对Redshift，请尝试

show table <**tablename**> ;

- Rishabh Chaurasiya

Answer 6

由于Redshift上不支持show table语句:

show table <YOUR_TABLE>;
ERROR: syntax error at or near "<YOUR_TABLE>"

我们可以使用pg_table_def表来获取模式信息：

select "column", type, encoding, distkey, sortkey, "notnull" 
from pg_table_def
where tablename = '<YOUR_TABLE>';

注意：如果模式不在搜索路径中，请使用以下命令将其添加到搜索路径中：

set search_path to '$user', 'public', '<YOUR_SCHEMA>';

- Nav

---

现在在Redshift中，SHOW TABLE <table_name>;命令可以正常工作了。 - Petrus Theron

确实，SHOW TABLE 现在可以在 Redshift 上使用。如果你的表是外部表，使用 SHOW EXTERNAL TABLE <table_name>。 - schiavuzzi

Answer 7

一种简单的方法是使用AWS提供的实用工具。您只需在数据库中创建视图，然后查询该视图以获取任何表的DDL。使用此视图的优点是它将提供原始创建表命令中使用的Sortkey和Distkey。

https://github.com/awslabs/amazon-redshift-utils/blob/master/src/AdminViews/v_generate_tbl_ddl.sql

创建视图后，要获取任何表的DDL，您需要像这样查询 -

select ddl from table where tablename='table_name' and schemaname='schemaname';

注意：在您的集群中可能没有管理模式。因此，您可以在公共模式中创建此视图。

- conetfun

Answer 8

在Postgres中，您可以查询目录。

在psql中使用简写来执行各种命令，您可以通过使用\?（帮助）获取命令列表。因此，以下任何一个都可以：

\d yourtable
\d+ yourtable

如果要在应用程序中使用，您需要学习相关的查询。可以运行psql -E(以显示隐藏查询)而不是普通的psql，这相对简单。

如果您需要精确的创建表语句，请参见@Anant的回答。

- Denis de Bernardy

Answer 9

以下查询将为您生成表的DDL：

SELECT ddl
FROM admin.v_generate_tbl_ddl
WHERE schemaname = '<schemaname>'
AND tablename in (
'<tablename>');

- Jai

Answer 10

你需要以编程方式检索还是从psql提示符中检索？

在psql中使用：\d+ tablename 以编程方式，您可以查询此处记录的ANSI标准INFORMATION_SCHEMA视图：

http://www.postgresql.org/docs/9.1/static/information-schema.html

你可以在INFORMATION_SCHEMA.TABLES和INFORMATION_SCHEMA.COLUMNS视图中找到所需的内容。

- codenheim