Questions about the MySQL query URL

If you want to query the URL, too long will affect the effect, so the article mentions to add a column for example URL_CRC, through the CRC32 function to query,
But I do not understand why the "this drawback is to maintain the hash" in the text, and manually create trigger maintenance will not have side effects?

Reply to discussion (solution)

Bizarre
CRC32 is not guaranteed to be unique, that is, different URLs may have the same CRC32 value
If you need to check the URL again when the CRC32 appears.
Then why not index the URL to query it?

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