正则表达式递归替换（增加缩进）

Question

我确信这应该是可能的，我想避免使用一个函数，因为它是一个页面上的一次性报告（Oracle 11g），但我真的很想用缩进的换行符格式化以下字符串对于每个后续替换“ - ”以显示层次结构

举个例子：

This is the base level - This is level 2 - And this is the second

所以，我可以开始并用换行符替换“ - ”并应用 CSS pre 以确保它们都在一行上

但理想情况下，我想要这样：

This is the base level
> This is level 2
>> And this is the second

在此先感谢

Answer 1

这有点丑，但有点工作（至少，我是如何理解这个问题的）。查看代码中的 cmets。

SQL> WITH test (col)
  2    -- Sample string
  3       AS (SELECT 'This is the base level - This is level 2 - And this is the second'
  4             FROM DUAL),
  5    -- Split it to rows (minus sign is a delimiter)
  6       temp
  7       AS (    SELECT LEVEL lvl,
  8                      TRIM (REGEXP_SUBSTR (col,
  9                                           '[^-]+',
 10                                           1,
 11                                           LEVEL))
 12                         val
 13                 FROM test
 14           CONNECT BY LEVEL <= REGEXP_COUNT (col, '-') + 1)
 15  -- join it back, using '>' along with CHR(10) as delimiter
 16  SELECT REPLACE (
 17            XMLAGG (XMLELEMENT (e, LPAD ('>', lvl - 1, '>') || val || CHR (10)) ORDER BY
 18                                                                                   lvl).EXTRACT (
 19               '//text()'),
 20            '&gt;',
 21            '>')
 22            result
 23    FROM temp;

RESULT
--------------------------------------------------------------------------------
This is the base level
>This is level 2
>>And this is the second


SQL>

---

如果你问“为什么是XMLAGG 而不是LISTAGG”，那是因为

 16  SELECT LISTAGG (val, LPAD ('>', lvl - 1, '>')) WITHIN GROUP (ORDER BY lvl)
 17    FROM temp;
SELECT LISTAGG (val, LPAD ('>', lvl - 1, '>')) WITHIN GROUP (ORDER BY lvl)
                                *
ERROR at line 16:
ORA-30496: Argument should be a constant.

Answer 2

如果填充在第一个参数中完成，您可以使用listagg：

with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1, regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(case when lvl > 1 then rpad(chr(10), lvl, '>') || ' ' end || result)
    within group (order by lvl) as result
from rcte
group by id
order by id;

ID | RESULT
-: | :--------------------------------------------------------------------------------
 1 | This is the base level
     > This is level 2
     >> And this is the second           
 2 | Base only                                                                        

但你也说过：

我可以开始并用换行符替换“ - ”并应用 CSS pre 以确保它们都在一行上

所以如果你想要一行，你就不能一开始就添加换行符：

with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1, regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(case when lvl > 1 then rpad(' ', lvl, '>') || ' ' end || result)
    within group (order by lvl) as result
from rcte
group by id
order by id;

ID | RESULT
-: | :-------------------------------------------------------------------------------
 1 | This is the base level > This is level 2 >> And this is the second              
 2 | Base only                                                                       

您还可以在递归 CTE 中添加 >，这可能会更整洁：

with rcte (id, value, lvl, result) as (
  select id, value, 1, regexp_substr(value, '(.*?)( - |$)', 1, 1, null, 1)
  from your_table
  union all
  select id, value, lvl + 1,
    rpad('>', lvl, '>') || ' ' || regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1)
  from rcte
  where regexp_substr(value, '(.*?)( - |$)', 1, lvl + 1, null, 1) is not null
)
select id,
  listagg(result, ' ') within group (order by lvl) as result
from rcte
group by id
order by id;

db<>fiddle