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sql-statements: document ALTER TABLE COMPRESSION='NONE' behavior #23299

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sql-statements: document ALTER TABLE COMPRESSION='NONE' behavior
takaidohigasi Jul 16, 2026
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sql-statement-alter-table.md を更新
takaidohigasi Jul 16, 2026
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2 changes: 2 additions & 0 deletions sql-statements/sql-statement-alter-table.md
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Expand Up @@ -189,6 +189,8 @@ The following major restrictions apply to `ALTER TABLE` in TiDB:

- `ALTER TABLE t CACHE | NOCACHE` is a TiDB extension to MySQL syntax. For details, see [Cached Tables](/cached-tables.md).

- `ALTER TABLE ... COMPRESSION` only accepts `NONE` (case-insensitive) and is a no-op. TiDB accepts this statement only for compatibility (for example, for tables migrated from MySQL that carry a `COMPRESSION` attribute) and does not compress or uncompress any table data. Specifying other values, such as `ZLIB` or `LZ4`, returns the error `This type of ALTER TABLE is currently unsupported` (error code 8200). If you specify an unsupported `COMPRESSION` value together with other options in a single statement, none of the options take effect.

@qiancai qiancai Jul 17, 2026

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The parser grammar requires COMPRESSION to be followed by stringLit, so bare NONE, ZLIB, and LZ4 do not reflect executable syntax. Keeping the quotes inside the code span also makes the MySQL-migration example immediately usable.

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- `ALTER TABLE ... COMPRESSION` only accepts `NONE` (case-insensitive) and is a no-op. TiDB accepts this statement only for compatibility (for example, for tables migrated from MySQL that carry a `COMPRESSION` attribute) and does not compress or uncompress any table data. Specifying other values, such as `ZLIB` or `LZ4`, returns the error `This type of ALTER TABLE is currently unsupported` (error code 8200). If you specify an unsupported `COMPRESSION` value together with other options in a single statement, none of the options take effect.
- `ALTER TABLE ... COMPRESSION` accepts only the string literal `'NONE'` (case-insensitive) and is a no-op. TiDB accepts this statement only for compatibility, for example, for tables migrated from MySQL that carry a `COMPRESSION` attribute. It does not compress or uncompress table data. Other values, such as `'ZLIB'` or `'LZ4'`, return error code 8200 (`This type of ALTER TABLE is currently unsupported`). If you specify an unsupported `COMPRESSION` value together with other options in a single statement, none of the options take effect.


For further restrictions, see [MySQL Compatibility](/mysql-compatibility.md#ddl-operations).

## See also
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