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Description

This error indicates that a BLOB or TEXT column is being used as part of a key specification (e.g., primary key, unique key, index) for a table type that does not support it. This typically occurs when the column's data type is too large or incompatible for direct indexing by the chosen storage engine.

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Error Message

BLOB column '%s' can't be used in key specification with the used table type

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Known Causes

3 known causes

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Direct BLOB/TEXT Key Usage

Attempting to define a primary key or unique key directly on a BLOB or TEXT column, which is generally not allowed due to the large size and variable length of these data types.

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Missing Index Prefix Length

Creating an index on a BLOB or TEXT column without specifying a required prefix length, which is necessary for many storage engines to index parts of the large column efficiently.

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Incompatible Storage Engine

Using a table storage engine (e.g., MEMORY) that has inherent limitations or does not support indexing BLOB or TEXT columns at all.

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Solutions

3 solutions available

1. Change BLOB to a Smaller Data Type easy

Replace the BLOB column with a smaller, indexable data type if the full BLOB is not required for indexing.

1

Identify the BLOB column causing the issue. The error message will usually specify the column name (e.g., '%s').

2

Determine if the entire BLOB content needs to be indexed. Often, a prefix or a derived value is sufficient.

3

If a prefix is acceptable, modify the table to add a new column of a suitable type (e.g., VARCHAR, VARBINARY) to store the prefix. Then, update this new column with the desired prefix from the original BLOB column.

ALTER TABLE your_table ADD COLUMN blob_prefix VARCHAR(255);
UPDATE your_table SET blob_prefix = LEFT(your_blob_column, 255);

4

If the BLOB column is no longer needed or can be entirely replaced by a smaller type, alter the table to change the column type. This might involve data loss if the original BLOB was larger than the new type's capacity.

ALTER TABLE your_table MODIFY COLUMN your_blob_column VARCHAR(255);

5

Once the column type is changed, you can create an index on the modified column or the new prefix column.

CREATE INDEX idx_blob_prefix ON your_table (blob_prefix);

2. Use a Full-Text Index for Text-Based BLOBs medium

For text-heavy BLOB columns, leverage MariaDB's full-text indexing capabilities instead of traditional key specifications.

1

Ensure your table uses a storage engine that supports full-text indexing (e.g., InnoDB, MyISAM).

2

Add a FULLTEXT index to the BLOB column. Note that this is only applicable if the BLOB column primarily stores text data that you intend to search within.

ALTER TABLE your_table ADD FULLTEXT(your_blob_column);

3

You can then use `MATCH() AGAINST()` syntax for searching within the BLOB column.

SELECT * FROM your_table WHERE MATCH(your_blob_column) AGAINST('search term');

3. Normalize the Table Structure advanced

Move the BLOB data to a separate, related table to avoid indexing issues in the primary table.

1

Create a new table to store the BLOB data, along with a foreign key referencing the original table.

CREATE TABLE your_table_blobs (
  id INT AUTO_INCREMENT PRIMARY KEY,
  parent_id INT NOT NULL,
  your_blob_column BLOB,
  FOREIGN KEY (parent_id) REFERENCES your_table(id) ON DELETE CASCADE
);

2

Move the BLOB data from the original table to the new `your_table_blobs` table. You'll need to populate the `parent_id` column with the appropriate primary key from `your_table`.

INSERT INTO your_table_blobs (parent_id, your_blob_column)
SELECT id, your_blob_column FROM your_table;

3

Remove the BLOB column from the original table.

ALTER TABLE your_table DROP COLUMN your_blob_column;

4

You can now create indexes on columns in the original `your_table` without issues. When you need to access the BLOB data, join the two tables.

SELECT t.*, b.your_blob_column
FROM your_table t
JOIN your_table_blobs b ON t.id = b.parent_id
WHERE t.some_indexed_column = 'some_value';

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Related Errors

5 related errors

MariaDB Error 1073: BLOB in Key Specification