<p>MySQL raises warning 1638 when a statement uses a non-ASCII character as a field or line separator, because the server does not fully support multibyte separators.</p>
<p>MySQL Error 1638 WARN_NON_ASCII_SEPARATOR_NOT_IMPLEMENTED signals that the separator character you passed is outside the ASCII range. Swap the separator for an ASCII byte such as comma or tab, or upgrade to a MySQL version that supports multibyte delimiters to clear the warning.</p>
Non-ASCII separator arguments are not fully supported
Error 1638 appears as a warning when you specify a non-ASCII character as a field, line, or string separator in functions like GROUP_CONCAT, statements such as LOAD DATA, or CSV export commands. MySQL detects the multibyte delimiter and notifies that full support is missing.
The warning does not always stop execution, but it can corrupt output or cause data to load incorrectly. Fixing it ensures predictable parsing and guards against hidden data loss.
The root cause is a separator character whose code point is above 0x7F. Examples include the pipe symbol copied from Unicode, emoji separators, or language-specific punctuation.
On builds prior to MySQL 8.0.34, internal string-handling routines assume single-byte delimiters. When faced with multibyte encodings, they fall back to ASCII-only logic and raise warning 1638.
The quickest fix is to replace the separator with a single-byte ASCII character such as comma (,), tab (t), or vertical bar (|). If your data requires multibyte separators, upgrade to a MySQL version that explicitly documents multibyte delimiter support.
After changing the SQL, rerun the statement and confirm that SHOW WARNINGS returns no row with code 1638.
When importing CSV with LOAD DATA, specify FIELDS TERMINATED BY ',' instead of '·'.
For GROUP_CONCAT, use CHAR(9) to insert a tab rather than a multibyte bullet character.
Export tools should be configured to emit ASCII delimiters before feeding the file into MySQL.
Standardize on ASCII delimiters in ETL pipelines and enforce them with code reviews.
Run automated tests that load sample files through Galaxy or CI and fail the build when warning 1638 appears.
Document accepted separators in database style guides and reference them in Galaxy Collections so all teammates reuse vetted syntax.
Using typographic bullets, accented punctuation, or emoji as delimiters in LOAD DATA triggers the warning because MySQL expects single-byte separators.
Passing CONCAT_WS('•', col1, col2) or GROUP_CONCAT(... SEPARATOR '•') raises 1638 when the bullet is multibyte.
Some code editors silently convert the ASCII pipe to a Unicode variant, leading to unexpected warnings during import.
Running a statement under utf8mb4 while the session assumes latin1 may cause a one-byte read that flags as non-ASCII.
Occurs when inserted data exceeds column limits. Unlike 1638, it involves value size not delimiters.
Raised by LOAD DATA when the separator clause is malformed. It blocks execution rather than issuing a warning.
Appears when LOCAL INFILE is disabled. It relates to security settings, not delimiter bytes.
Signals that a feature will be removed in future versions. Similar to 1638 in being non-fatal.
No. It is a warning. The statement completes, but output may be corrupted if multibyte separators are misread.
Ignoring is risky. Downstream tools may split fields incorrectly. Always switch to ASCII or upgrade MySQL first.
Versions before 8.0.34 are the usual culprits, though the warning text remains identical across 5.7 and 8.0.
Galaxy highlights server warnings in its results pane, lets you test alternative separators quickly, and stores endorsed queries so teams standardize on ASCII delimiters.
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