fix: only run nested sub-query for SELECT templates with ${...} (#4)

[y-ken]

Summary

Fixes #4: in mysql_replicator (single), a column value that merely begins with "SELECT" triggered an unintended nested sub-query, so ordinary text data could be executed as SQL.

📌 Stacked on #51 . Base is fix/delete-detection-range to keep the diff clean and avoid a conflict in the shared test file; GitHub will retarget this to master once #51 merges.

Background — why #4 was still open

The maintainer proposed the correct fix back in 2014 and #6 applied it — but only to in_mysql_replicator_multi.rb:

file	regex
multi (in_mysql_replicator_multi.rb)	/^SELECT[^\$]+\$\{[^\}]+\}/i ✅ (fixed in #6)
single (in_mysql_replicator.rb)	/^SELECT(\s+)/i ❌ still fires without a placeholder

#4 was reported against the single plugin, which never received the fix. This PR ports the proven multi regex to single so the two behave consistently.

Fix

Require a ${placeholder} before treating a value as a sub-query template, and extract the predicate for testing:

def nested_query_value?(value)
  value.to_s.strip.match?(/^SELECT[^\$]+\$\{[^\}]+\}/i)
end

So "SELECT * FROM child WHERE parent_id = ${id}" still nests, while a data value like "SELECT YOUR PLAN" is left alone.

Tests

Added regression tests: a real template (true), plain text starting with "SELECT", the word "Selecting", a SELECT without a placeholder, and non-string values (all false).

Verified locally on Ruby 3.4 (11 tests, 17 assertions, 0 failures — includes #51's tests since this is stacked).

Closes #4

🤖 Generated with Claude Code