AWS中的序号生成函数redshift

Question

redshift中是否有序号生成函数？还是一个组合了值并且给出数字哈希键的函数？

Answer 1

目前没有序列的概念（如Oracle中所见）。

您有几种选择：在整套

• 号码表
• RANK（）或ROW_NUMBER（）的窗函数。请注意，如果您拥有多节点群集，则可能会产生一些负面的性能影响。
• 定义为IDENTITY（seed，step）的列。请注意，IDENTITY序列可能是'稀疏'（例如，序列中有空位）。

Answer 2

我是Redshift的新手，我发现本文寻找一个常见的序列，这在Amazon数据库中不受支持。我发现这个解决方案我会用一个完整的例子报告，使用ROW_NUMBER。

我有模式sta and dim。在sta我有临时表，而在昏暗我有维度表我想用ID填充。我有一个信息来源，其中包含字段trk_key，名称包含例如一些发布者。

CREATE TABLE sta.publisher (
     trk_key VARCHAR(20), 
     name VARCHAR(225) 
); 
CREATE TABLE dim.publisher (
     id SMALLINT, 
     trk_key VARCHAR(20), 
     name VARCHAR(255), 
     PRIMARY KEY (id) 
); 

首先我截断sta.publisher表并加载有一个CSV文件。然后我启动下面的查询

-- This query is idempotent: 
-- it will insert a publisher found in sta.publisher table only if 
-- it is not already in dim.publisher table. 
INSERT INTO dim.publisher 
SELECT 
     -- Generate id using max id found in dim.publisher. 
     -- Start with id=1 if dim.publisher is empty. 
     (
       SELECT NVL(MAX(id), 0) 
       FROM dim.publisher 
     ) + ROW_NUMBER() OVER() AS id, 
     trk_key, 
     name 
FROM sta.publisher 
     -- Only insert record if trk_key is not found in dim.publisher table. 
     WHERE trk_key NOT IN (
       SELECT trk_key 
       FROM dim.publisher 
     ) 

Answer 3

这里是另一种方式产生1万个号码

with seq_0_9 as (
select 0 as num 
union all select 1 as num 
union all select 2 as num 
union all select 3 as num 
union all select 4 as num 
union all select 5 as num 
union all select 6 as num 
union all select 7 as num 
union all select 8 as num 
union all select 9 as num 
), seq_0_999 as (
select a.num + b.num * 10 + c.num * 100 as num 
from seq_0_9 a, seq_0_9 b, seq_0_9 c 
) 
select a.num + b.num * 1000 as num 
from seq_0_999 a, seq_0_999 b 
order by num 

Answer 4

您仍然可以查询Posgres功能generate_series(start, stop, step)

但它不是一个支持的功能，只能运行在领导节点上，这使得它相当无用，但嘿，你仍然可以select generate_series(1,100)并获得100个数字的列表。你只能在领导者节点上用而不是做任何事情。

http://docs.aws.amazon.com/redshift/latest/dg/c_unsupported-postgresql-functions.html