Remove simple HTML-Tags from String in Oracle via RegExp, Explanation needed

Question

I do not understand, why my columns reg1 and reg2 remove "bbb" from my string, and only reg3 works as expected.

WITH t AS (SELECT 'aaa <b>bbb</b> ccc' AS teststring FROM dual)

SELECT
  teststring,
  regexp_replace(teststring, '<.+>') AS reg1,
  regexp_replace(teststring, '<.*>') AS reg2,
  regexp_replace(teststring, '<.*?>') AS reg3
FROM t


TESTSTRING             REG1        REG2          REG3
aaa <b>bbb</b> ccc     aaa ccc     aaa ccc       aaa bbb ccc

Thanks a lot!

Aronarondel

Answer 1

Because regex is greedy by default. I.e. the expressions .* or .+ try to take as many characters as possible. Therefore <.+> will span from the first < to the last >. Make it lazy by using the lazy operator ?:

regexp_replace(teststring, '<.+?>')

or

regexp_replace(teststring, '<.*?>')

Now, the search for > will stop at the first > encountered.

Note that . includes > as well, therefore the greedy variant (without ?) swallows all the > but the last.

Lipcombe

Thanks a lot! I thought, ? stands only for "one or zero". – Aronarondel

? stands for "one or zero" unless when occuring after a quanitfier, where it stands as lazy operator. See: Lazy quantification. – Lipcombe

Answer 2

You can remove HTML tags from string

REGEXP_REPLACE (teststring,'<[^>]*>',' ')

Scotland

Although your answer is correct in the sense of obtaining the result expected by the OP, the OP was asking a why some of his code worked and some didn't work, he already had an answer, and was looking for an explanation. The explanation was provided 7 years ago, and your answer doesn't answer that question, and is posted in an old thread. – Mccourt

Answer 3

Because the first one and the second one are finding this match: <b>bbb</b> - in this case b>bbb</b matches both .* and .+

The third one also won't do what you need. You are looking for something like this: <[^>]*>. But you also need to replace all matches with ""

Hershey

The third one do exacly what I need. I didn't understand, why. @Olivier gave the useful answer. – Aronarondel

Answer 4

If you are merely trying to display the string without all the HTML tags, you can use the function: utl_i18n.unescape_reference(column_name)

Alow

A late response but unescape_reference only replaces the tags for &lt;, etc. It doesn't strip out any other HTML (e.g. <p>). – Coincide