UNNEST 多个值?

UNNEST Multiple Values?

我正在尝试从另一个 table 中制作一个 table。原来的 table 有一行看起来像这样:

------------------------
| col1 | col 2 | col 3 |
------------------------
| item | a,b,c | 1,2,3 |
------------------------

我正在尝试将该行放入 table 中,如下所示:

------------------------
| col1 | col 2 | col 3 |
------------------------
| item |   a   |   1   |
------------------------
| item |   b   |   2   |
------------------------
| item |   c   |   3   |
------------------------

所以基本上我试图同时 UNNEST 两个逗号分隔的行。到目前为止,我想出的最好的办法是分别对每一列进行 UNNEST,然后尝试将两个结果 tables 组合起来(我也在努力解决),但理想情况下我希望将其合二为一步骤.

这是我一次 UNNEST 一行的查询:

SELECT
  col1, col2, col3
FROM 
  tableName,
UNNEST(SPLIT(col2)) AS col2

这是我尝试将 UNNEST 作为子查询执行的尝试,但它给出了大量结果:

SELECT sub.*
FROM (
  SELECT
    col1, col2, col3 AS col3
  FROM 
    tableName,
  UNNEST(SPLIT(col2)) AS col2
  WHERE
    randomCol = 'something'
  ) sub,
UNNEST(SPLIT(sub.col3)) AS col3

说原来的 table 有 'a row':你是说一个吗?如果是,这就可以了:

with 
num_rows_ as (
  select length( regexp_replace((select b from t), '[^,]+')) + 1 value_ from dual),
a_ as (
  select a from t),
b_ as (
  select regexp_substr( (select b from t), '[^,]', 1, level ) b,rownum rownum_
  from dual
  connect by level <= (select value_ from num_rows_)),
c_ as (
  select regexp_substr( (select c from t), '[^,]', 1, level ) c,rownum rownum_
  from dual
  connect by level <= (select value_ from num_rows_))  
select a_.a,b_.b,c_.c 
  from a_ 
  full outer join b_ on 1=1
  inner join c_ on b_.rownum_ = c_.rownum_;

http://sqlfiddle.com/#!4/f795b9/29

或更短,一步完成:

with a_ as
(select a from t),
b_c_ as (
  select regexp_substr( (select b from t), '[^,]', 1, level ) b,regexp_substr( (select c from t), '[^,]', 1, level ) c
  from dual
  connect by level <= (length( regexp_replace((select b from t), '[^,]+')) + 1)
)
select * from a_ cross join b_c_;

http://sqlfiddle.com/#!4/f795b9/32/0

您可以使用 unnest(split(col)) 策略,但不要交叉连接两列。您的回答暗示了逗号分隔值的隐含顺序,因此您需要建立一个字段(下面的 RowNumber)来指示此顺序。

with Expanded2 as (
  select
    tableName.col1,
    col2.col2,
    row_number() over (partition by col1 order by 1) RowNumber
  from
    tableName,
    unnest(split(col2)) col2
), Expanded3 as (
  select
    tableName.col1,
    col3.col3,
    row_number() over (partition by col1 order by 1) RowNumber
  from
    tableName,
    unnest(split(col3)) col3
)
select
  Expanded2.col1,
  Expanded2.col2,
  Expanded3.col3
from
  Expanded2
  full outer join Expanded3 on 
    Expanded2.col1 = Expanded3.col1
    and Expanded2.RowNumber = Expanded3.RowNumber

我不确定您的 rdbms 如何处理有效的空 window 分区。以上在 PostgreSQL 中有效。 SQL 服务器需要 order by (select null)。 Ymmv.

SQL 标准允许将多个值传递给 unnest() 函数。

因此以下内容应该有效(并且在 Postgres 中有效)

select d.col1, 
       t.*
from data d
  cross join unnest(string_to_array(d.col2, ','), string_to_array(d.col3, ',')) as t(col1, col2) 

这也能正确处理列表中不同数量的元素。

但是,我不知道您的专有 DBMS 是否支持它。

在线示例:http://rextester.com/XPN48947