A binary large object, or BLOB, is a database type for storing variable-length data as bytes rather than interpreting it as ordinary character text. Images, audio, and video are common examples of content stored this way, but a BLOB is not itself a media format—and the type’s name, size limits, and storage behavior depend on the database.
What does BLOB mean?
BLOB stands for “binary large object.” MySQL defines a BLOB as a binary large object that can hold a variable amount of data. In practical terms, the database stores the content as bytes without applying character-set semantics to those bytes. MySQL Reference Manual, version 26.7; Oracle Database 26 SQL Reference.
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The bytes might represent an image, audio recording, video, or other binary content. The BLOB type does not identify or validate the file format; an application must determine how the bytes should be interpreted. Oracle Database 26 SQL Reference.
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A BLOB is for binary data, whereas a text type is for character data. MySQL distinguishes binary BLOB strings from nonbinary TEXT strings, which have character-set semantics. A related Oracle distinction is BLOB versus CLOB or NCLOB: the former stores binary large objects, while the latter types store character data. MySQL Reference Manual, version 26.7; Oracle Database SecureFiles and Large Objects Developer’s Guide, 21c.
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Choosing a BLOB does not by itself provide file-format checks, application-level permissions, or a lifecycle policy. Those responsibilities depend on the database design and the software using it.
How databases implement binary large objects
“BLOB” does not name one universal storage mechanism or size limit. The database product and release determine the type names and behavior.
| Database documentation | Binary storage options described | Important qualification |
|---|---|---|
| MySQL Reference Manual, version 26.7 | TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB |
The four types have different maximum lengths; consult the manual for the applicable limits. Source. |
| Oracle Database 26 SQL Reference | BLOB |
The documented maximum is expressed as (4 gigabytes − 1) multiplied by the LOB storage CHUNK; the chunk relates to database block size. It is not a single universal BLOB limit. Source. |
| PostgreSQL 17 | bytea columns and a separate Large Object facility referenced by an OID |
The documentation describes these as PostgreSQL’s binary data options rather than a literal SQL BLOB type. Source. |
| SQL Server 2008 R2 and SQL Server 2012 standards-variance documentation | varbinary as equivalent functionality |
This cited Microsoft page addresses those versions; it should not be read as a statement about every SQL Server release. Source. |
Because names and limits vary, check the documentation for the exact database product and release before choosing a column type or estimating capacity.
PostgreSQL: a column value or a separate Large Object?
PostgreSQL documents bytea for binary data stored in a column and a separate Large Object mechanism, where a value is referenced by an OID. The pgJDBC guide says Large Objects can suit very large values, but they have additional operational responsibilities. PostgreSQL 17 Documentation; pgJDBC, “Storing Binary Data”.
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- Cleanup: Deleting a row that contains a Large Object reference does not itself delete the referenced Large Object. Applications must handle its removal explicitly.
- Access control: Permissions on Large Objects do not necessarily follow permissions on the row that references them. Design and verify access rules for both.
What to check before using a BLOB type
There is no universal rule that binary files should always be stored inside a database or always outside it. Evaluate the relevant product behavior and workload rather than relying on the word “large.”
Quick Recap
- Confirm the database product and release, and whether it supports a type literally named
BLOB. - Check the maximum value size and whether the limit depends on configuration or storage settings.
- Find out whether data is kept in a column or through a separate large-object mechanism.
- Review the product’s documented read, write, and transaction behavior for the operations your application needs.
- Plan permissions, backup handling, and cleanup—especially when binary objects are stored separately from their referencing rows.
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