No, Codility does not check for plagiarism on SQL tasks.
When it comes to SQL tasks, we are unable to run our similarity checkers over your candidates' solutions due to the innate similarity we expect between candidates. With SQL tasks, it is possible to have 20-50% of identical solutions just by pure coincidence due to the nature of the SQL language.
If you have any additional questions about your candidate's solution or would like to leave your feedback, please reach out to your Customer Success Manager, contact us at support@codility.com or read our anti-plagiarism process.