How can REGEXP_REPLACE add a character after every alphanumeric sequence?

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To add a character after every alphanumeric sequence using REGEXP_REPLACE, we can use a regular expression pattern that matches any alphanumeric sequence and replace it with the same sequence followed by the desired character. Here is an example SQL statement that adds a underscore character after every alphanumeric sequence:

SELECT REGEXP_REPLACE('abc123def456', '([[:alnum:]]+)', '\1_')

Output:

abc_123def_456

In this example, the regular expression pattern ([[:alnum:]]+) matches any sequence of one or more alphanumeric characters. The replacement string \1_ replaces the matched sequence with itself followed by an underscore character. The \1 is a backreference that refers to the matched sequence in the pattern.