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Description

MySQL Error 1850 occurs when an `ALTER TABLE` statement attempts to modify a column's data type using the `INPLACE` algorithm, but the specific type conversion is not supported for an in-place operation. This means the requested change requires MySQL to rebuild the entire table, which cannot be done without a full table copy.

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Error Message

Cannot change column type INPLACE

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Known Causes

3 known causes

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Unsupported Column Type Conversion

The specific data type change requested (e.g., from `INT` to `VARCHAR`, or certain `VARCHAR` to `TEXT` conversions) fundamentally alters the column's storage structure, making an `INPLACE` alteration impossible.

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Storage Engine Limitations

Certain storage engines or their versions may have restrictions on which column type alterations can be performed `INPLACE`, requiring a full table rebuild for the requested change.

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Combined Schema Changes

If the `ALTER TABLE` statement includes multiple complex modifications alongside the column type change, MySQL might collectively determine that an `INPLACE` operation is not feasible.

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Solutions

3 solutions available

1. Use `ALGORITHM=COPY` for the Alter Table Operation easy

Explicitly instruct MySQL to perform a table copy, bypassing the INPLACE restriction.

1

When altering the column type, specify `ALGORITHM=COPY`. This forces MySQL to create a new table with the desired schema and copy the data over.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name new_data_type [other_options], ALGORITHM=COPY;

2

Execute the `ALTER TABLE` statement.

2. Create a New Table and Migrate Data medium

A robust method for complex alterations, especially when INPLACE is consistently failing or not supported.

1

Create a new table with the desired schema, including the modified column type.

CREATE TABLE new_your_table_name LIKE your_table_name;
ALTER TABLE new_your_table_name MODIFY COLUMN your_column_name new_data_type [other_options];

2

Copy the data from the original table to the new table.

INSERT INTO new_your_table_name SELECT * FROM your_table_name;

3

Drop the original table.

DROP TABLE your_table_name;

4

Rename the new table to the original table's name.

RENAME TABLE new_your_table_name TO your_table_name;

3. Disable Binary Logging Temporarily (if applicable) medium

In some specific scenarios, binary logging can interfere with INPLACE operations. This is a quick but potentially risky fix.

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Check your MySQL configuration for `log_bin`. If it's enabled, you might consider temporarily disabling it. **Caution:** This is not recommended for production environments without understanding the implications for replication and point-in-time recovery.

SET GLOBAL log_bin = OFF;
-- Or, edit my.cnf/my.ini to comment out log_bin and restart MySQL.

2

Perform the `ALTER TABLE` operation.

ALTER TABLE your_table_name MODIFY COLUMN your_column_name new_data_type [other_options];

3

Re-enable binary logging if you disabled it dynamically. If you edited configuration files, restart the MySQL server.

SET GLOBAL log_bin = ON; -- If you set it dynamically

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Related Errors

5 related errors

MySQL Error 1850: In-Place Column Type Alteration