修改Oracle正则表达式：仅允许域名前缀含2个及以上字符

Hey there! Let's tackle this regex issue you're facing. Your current pattern is letting through emails like a@b.com because it allows single-character domain labels (that's the b before the .com). We need to adjust things so only labels with 2 or more total characters are allowed—whether they're plain alphanumeric (like bb) or hyphenated (like b-domain).

Updated Regex #

Here's the revised pattern that meets your requirements:

@((?:[A-Z0-9]{2,}|[A-Z0-9]+-[A-Z0-9]+)(?:-[A-Z0-9]+)*\.){1,8}[A-Z]{2,63}$

What Changed & Why #

Let's break down the key adjustment:

• The original part [A-Z0-9]+ (which matched 1+ alphanumeric characters) was replaced with (?:[A-Z0-9]{2,}|[A-Z0-9]+-[A-Z0-9]+). This does two things:
  1. [A-Z0-9]{2,}: Ensures plain alphanumeric labels have at least 2 characters (so bb passes, b fails).
  2. [A-Z0-9]+-[A-Z0-9]+: Allows hyphenated labels, but only if there's at least one character before and after the hyphen (so b-domain passes, while invalid labels like b- or -domain get blocked—though those aren't valid domain labels anyway).
• The rest of the pattern ((?:-[A-Z0-9]+)*\.){1,8}[A-Z]{2,63}$) stays intact to support multiple hyphens in labels and valid top-level domain (TLD) lengths.

Testing Your Examples #

Let's verify against your test cases:

• a@b.com: Invalid → The label b is only 1 character, which doesn't meet the minimum requirement.
• a@bb.com: Valid → The label bb has 2 alphanumeric characters, which checks out.
• a@b-domain.com: Valid → The hyphenated label b-domain has characters both before and after the hyphen, totaling more than 2 characters.

If you need to enforce this minimum length for all domain labels (not just the first one after @), this pattern works for that too—any subdomain label (like sub in a@sub.bb.com) will also need to meet the 2-character minimum.

内容的提问来源于stack exchange，提问作者user11311005