How to use backreferences beyond 9 in a PostgreSQL regular expression?

Question

The following regex simply extracts a part of the matched text using the backreferencing numbers:

SELECT regexp_replace('ABCDEFGHIJ','(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)','\2');
B

But how to backreference beyond the ninth matched substring?

The following won't work (returns the first match + 0), neither will the use of $10 or ${10}:

SELECT regexp_replace('ABCDEFGHIJ','(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)(\w)','\10')
A0

Note: this example was simplified for clarity, and would of course not necessitate going beyond backreference 9.

Answer 1

根据文档，模式字符串中支持大于 9 的反向引用：

\mnn（其中m是非零数字，并且nn是更多数字，并且小数值mnn不大于迄今为止看到的右捕获括号的数量）对第mnn'th 子表达式的反向引用

但是，似乎它们在以下位置的替换字符串中不受支持regexp_replace：

该replacement字符串可以包含\n，其中n1 到 9，以指示n应插入与模式的第 ' 个带括号的子表达式匹配的源子字符串...