MySQL raises error 1073 when you try to define a primary, unique, or foreign key on a BLOB or TEXT column, which these storage types do not support.
MySQL Error 1073: ER_BLOB_USED_AS_KEY appears when you attempt to index or declare a key on a BLOB or TEXT column. Convert the column to VARCHAR with a length or add a prefix length to the index to resolve the issue.
BLOB column '%s' can't be used in key specification with
Error 1073 fires when a CREATE TABLE or ALTER TABLE statement includes a BLOB or TEXT column inside a PRIMARY KEY, UNIQUE KEY, or FOREIGN KEY clause. These large-object types have variable length and cannot be used directly in MySQL key specifications.
Because keys drive fast lookups and enforce uniqueness, MySQL needs length-bounded, comparable data types.
BLOB and TEXT lack that guarantee, so the server blocks the operation and returns SQLSTATE 42000.
Placing a BLOB or TEXT column in a PRIMARY KEY definition is the most common trigger.
Developers often store JSON or large strings in BLOB/TEXT, then attempt to enforce uniqueness with a key.
Adding a UNIQUE constraint to a BLOB/TEXT column during table alteration also triggers error 1073, as does referencing such a column in a FOREIGN KEY constraint.
Change the column type to VARCHAR with an appropriate length when the stored data never exceeds MySQL’s 65,535-byte row limit and needs exact matching.
This satisfies key requirements.
When a full change is impossible, create an index on a prefix length of the BLOB/TEXT column. MySQL permits indexes such as INDEX idx_name(column(255)), effectively using the first N bytes for comparisons.
Storing UUID strings as BLOB(16) then adding a PRIMARY KEY fails. Convert the column to BINARY(16) or CHAR(36) and reapply the key.
Attempting to reference a TEXT comment field in a child table’s FOREIGN KEY fails.
Instead, create a surrogate numeric key in the parent table and reference that column.
Design schemas so keys use fixed-length or length-defined columns like INT, BIGINT, CHAR, or VARCHAR. Reserve BLOB/TEXT for non-indexed data only.
Enable continuous schema linting in tools like Galaxy’s AI copilot.
It flags illegal key definitions before execution, preventing runtime errors.
Error 1170 (BLOB/TEXT column used in key without key length) occurs when a prefix length is omitted. Specify a length such as INDEX(txt(100)).
Error 1071 (Specified key was too long) surfaces when the combined key length exceeds the allowed limit. Reduce column lengths or split the index.
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Declaring a BLOB or TEXT column as the table’s PRIMARY KEY immediately triggers error 1073 because MySQL disallows variable-length LOBs in primary indexes.
Applying UNIQUE to comment, description, or JSON columns of type TEXT or MEDIUMTEXT fails for the same reason: the engine cannot maintain uniqueness efficiently.
When a child table uses a BLOB/TEXT column to reference a parent key, InnoDB rejects the statement since referenced columns must be indexed and length-bounded.
Adding AUTO_INCREMENT to a BLOB/TEXT column implicitly creates a primary key, again violating key rules and resulting in error 1073.
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Occurs when you index a BLOB/TEXT column but forget to specify a prefix length. Add (column_name(N)) after the column.
Appears when the total length of all indexed columns exceeds the storage engine limit.
Reduce field sizes or column count.
Often raised when trying to create a foreign key that references a non-indexed or unsupported column type such as BLOB/TEXT.
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Yes, but only by specifying a prefix length. For example, INDEX (mytext(100)) indexes the first 100 bytes, which is often sufficient for filtering.
VARCHAR works for keys as long as the combined length of indexed columns stays below the engine limit (3072 bytes for InnoDB in MySQL 8.0).
ALTER TABLE ... MODIFY preserves data when converting between compatible types such as TEXT to VARCHAR. Always back up before altering production tables.
Galaxy’s schema-aware AI copilot inspects CREATE/ALTER statements and warns when a BLOB/TEXT column appears in a key clause, suggesting safer alternatives.
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