<p>MySQL raises ER_UNKNOWN_EXPLAIN_FORMAT (code 1791) when the EXPLAIN FORMAT value is misspelled or unavailable in the server version.</p>
<p>MySQL Error 1791: ER_UNKNOWN_EXPLAIN_FORMAT appears when you run EXPLAIN FORMAT=xyz and xyz is not one of MySQL's supported formats (TRADITIONAL, JSON, TREE). Correct the FORMAT keyword or upgrade MySQL to resolve the error.</p>
Unknown EXPLAIN format name: '%s'
Error 1791 occurs when you execute an EXPLAIN statement with an unsupported or misspelled FORMAT option. MySQL cannot map the provided string to a valid formatter and stops execution.
The error text reads: Unknown EXPLAIN format name: '%s'. It interrupts query analysis but does not affect data. Fixing it lets you inspect execution plans again.
The error surfaces most often after a typo in the FORMAT clause, such as FORMAT=JSN or FORMAT=TRADTIONAL. MySQL only accepts TRADITIONAL, JSON, TREE and, in older releases, PROFILE.
A second cause is using a newer FORMAT keyword on an older server version that lacks support, for example FORMAT=TREE on MySQL 5.6.
First, check spelling. Ensure the keyword exactly matches TRADITIONAL, JSON or TREE. Second, confirm your MySQL version supports the requested format. Upgrade or switch formats if necessary.
If you connect through tools or ORMs, verify they generate a supported FORMAT value. Updating the client library often resolves mismatches.
Developers migrating scripts from MySQL 8.0 to 5.7 may hit the error because TREE is unsupported in 5.7. Change to JSON or upgrade the server to 8.0.
Automation that builds FORMAT clauses dynamically can introduce blanks or mixed-case strings. Trim inputs and enforce uppercase constants to avoid runtime failures.
Standardize on JSON format in shared scripts because it remains backward compatible to 5.7. Place FORMAT value in a constant to eliminate typos.
Include a version check in deployment pipelines that prevents new code from using unsupported formats on legacy environments.
ER_PARSE_ERROR appears when the EXPLAIN syntax itself is wrong, not just the FORMAT name. Verify full statement structure.
ER_NOT_SUPPORTED_YET may arise if you try TREE on views or partitioned tables in older 8.0 minors. Upgrade to the latest patch level.
Using FORMAT=JSN instead of FORMAT=JSON immediately triggers the unknown format error.
Running FORMAT=TREE on MySQL 5.7 or earlier causes the error because those versions do not include the TREE formatter.
Older connectors hard-code FORMAT=PROFILE, which was removed in MySQL 8.0, generating the error when run on modern servers.
Automated tooling that concatenates FORMAT values may introduce trailing spaces or lowercase letters, leading MySQL to misinterpret the option.
Occurs when the EXPLAIN statement has invalid syntax beyond the FORMAT clause. Fix grammar or punctuation.
Raised when a valid syntax element is not yet implemented for the object in your MySQL version.
Appears if the FORMAT string is NULL or an empty literal, indicating type mismatch.
No. The error stops only the EXPLAIN command and does not modify or corrupt data.
JSON is widely supported from MySQL 5.7 onward and is easy to parse programmatically.
TREE offers a human-friendly, indented layout but requires MySQL 8.0.16+. Use it for quick visual inspection, JSON for automated analysis.
Galaxy's context-aware autocomplete lists only server-supported FORMAT values, preventing typos and version mismatches before query execution.
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