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    MaxCompute:GET_BLOB_METADATA

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    MaxCompute:GET_BLOB_METADATA

    Last Updated:Oct 09, 2026

    The GET_BLOB_METADATA() function retrieves the metadata of a blob. You can use JSON functions to extract specific fields from the returned JSON object.

    Common usage

    GET_JSON_OBJECT(GET_BLOB_METADATA(blob_expr), '$.field_name');

    Usage notes

    • The GET_BLOB_METADATA() function takes a single blob parameter.

    • You can extract fields from the returned JSON object.

    • Common fields include: content_type, content_length, checksum, is_compressed, content_encoding, storage_type, and blob_storage_tier.

    • content_length represents the length in bytes and is suitable for validation with lengthb().

    • is_compressed indicates whether the content is compressed, and content_encoding specifies the compression encoding.

    • The function returns NULL if the input blob is NULL or empty.

    Syntax

    JSON GET_BLOB_METADATA(blob_expr:BLOB)

    Parameters

    blob_expr (Required): An expression of the BLOB type.

    • The function accepts a single blob parameter.

    • The parameter must be a blob expression.

    • Common sources include the to_blob(...) function, a blob column in a table, or a blob column generated by a CREATE TABLE AS SELECT (CTAS) or INSERT SELECT statement.

    Examples:

    GET_BLOB_METADATA(to_blob('abcdef'))
GET_BLOB_METADATA(to_blob('hello world', 'text/plain'))
GET_BLOB_METADATA(b)

    Return value

    Returns a JSON object containing the metadata. The following table describes the common fields in this object.

    Typically, you retrieve the value of a specific field instead of the entire object.

    Field name

    Description

    content_type

    The content type specified when the blob was created. Common use cases include:

    • Verify that the to_blob(..., content_type) expression was applied.

    • Distinguish between different types, such as text/plain and application/json.

    content_length

    The size of the blob content in bytes. For example:

    • For to_blob('abcdef'), the value is 6.

    • For to_blob(X'616263'), the value is 3.

    • to_blob('Chinese test') returns 12

    • For empty content, the value is 0.

    checksum

    A checksum of the content. You can use this field to determine if the content or storage object is consistent. Returns NULL if no checksum is available.

    is_compressed

    Indicates whether the blob is stored in a compressed format. Current observations show:

    • Small blobs created directly typically have a value of false.

    • Larger, persisted blobs may have a value of true.

    • Compression depends on the underlying storage and codec.

    These examples do not represent all possible compression rules.

    content_encoding

    The name of the compression encoding.

    • If is_compressed = false, the value is NULL

    • If is_compressed = true, the actual codec name is returned.

    storage_type

    The storage type of the blob. This field is useful for troubleshooting the blob's storage format.

    blob_storage_tier

    The storage tier of the blob. Returns NULL if this information is unavailable.

    NULL handling

    • When the input parameter is NULL or an empty blob

      The GET_BLOB_METADATA(blob_expr) function returns NULL in the following scenarios:

      • The input parameter itself is NULL.

      • The blob is empty.

      • The blob does not contain valid readable content.

      -- Returns: NULL
SELECT GET_BLOB_METADATA(to_blob(CAST(null as binary)));

-- In this case, if you try to extract a field, the result is also NULL.
SELECT get_json_object(GET_BLOB_METADATA(to_blob(CAST(null as binary))), '$.content_length');

    • When a field in the returned result is NULL

      Even if GET_BLOB_METADATA(blob_expr) does not return NULL, some of its fields may be null.

      Common scenarios include:

      • content_type: The value is NULL if a content type is not specified.

      • checksum: Is NULL if no corresponding checksum is available.

      • content_encoding: Is NULL when uncompressed.

      • blob_storage_tier: Is NULL if no corresponding storage tier information is available.

    • The two scenarios for NULL values have distinct meanings:

      • The function returns NULL because the blob has no metadata to return.

      • A field is NULL: The metadata exists, but the field currently has no value.

    Examples

    Read metadata directly

    SELECT GET_BLOB_METADATA(to_blob('abcdef'));

-- Return value:
{
    "checksum": null,
    "content_type": null,
    "storage_type": "MEMORY",
    "is_compressed": false,
    "content_length": 6,
    "content_encoding": null,
    "blob_storage_tier": "STANDARD"
}

    Read the three most common fields

    This is useful for quickly checking the content type, size in bytes, and compression status.

    SELECT
  get_json_object(GET_BLOB_METADATA(to_blob('abcdef')), '$.content_type'),
  get_json_object(GET_BLOB_METADATA(to_blob('abcdef')), '$.content_length'),
  get_json_object(GET_BLOB_METADATA(to_blob('abcdef')), '$.is_compressed');

-- Return value:
+------------+------------+------------+
| _c0        | _c1        | _c2        | 
+------------+------------+------------+
| NULL       | 6          | false      | 
+------------+------------+------------+

    Validate the application-written content type

    SELECT get_json_object(
  GET_BLOB_METADATA(to_blob('{"key":"value"}', 'application/json')),
  '$.content_type'
);

-- This confirms that the specified content type was correctly set.
+--------------------+
| _c0                | 
+--------------------+
| application/json   | 
+--------------------+

    Validate the content length

    SELECT cast(
  get_json_object(GET_BLOB_METADATA(to_blob('中文测试')), '$.content_length') as bigint
);

-- Return value:
+------------+
| _c0        | 
+------------+
| 12         | 
+------------+

    Validate consistency with LENGTHB()

    SELECT
  LENGTHB(TO_BLOB('abcdef')),
  CAST(GET_JSON_OBJECT(GET_BLOB_METADATA(TO_BLOB('abcdef')), '$.content_length') AS BIGINT);

-- Return value:
+------------+------------+
| _c0        | _c1        |
+------------+------------+
| 6          | 6          |
+------------+------------+

    Check persisted blob compression

    1. Prepare a test table.

      -- Create a table that contains a BLOB column.
CREATE TABLE blob_table2 (
  col1 INT ,
  col2 BLOB
)
TBLPROPERTIES (
  "table.format.version"="2" 
);

-- Write data to the table.
INSERT INTO blob_table2 VALUES (1, to_blob(repeat('aaa', 1000), 'application/json'));

-- Read data from the table.
SELECT col1,read_blob(col2) FROM blob_table2;

    2. Query the compression status.

      SELECT 
  get_json_object(GET_BLOB_METADATA(col2), '$.is_compressed') 
FROM blob_table2;

-- Return value:
+------+
| _c0  |
+------+
| true |
+------+

      is_compressed indicates whether the blob is currently stored in a compressed format.

    View the compression encoding

    1. Prepare a test table.

      -- Create a table that contains a BLOB column.
CREATE TABLE blob_table2 (
  col1 INT ,
  col2 BLOB
)
TBLPROPERTIES (
  "table.format.version"="2" 
);

-- Write data to the table.
INSERT INTO blob_table2 VALUES (1, to_blob(repeat('aaa', 1000), 'application/json'));

-- Read data from the table.
SELECT col1,read_blob(col2) FROM blob_table2;

    2. View the compression encoding.

      SELECT
  get_json_object(GET_BLOB_METADATA(col2), '$.is_compressed'),
  get_json_object(GET_BLOB_METADATA(col2), '$.content_encoding')
FROM blob_table2;

-- Return value:
+------+------+
| _c0  | _c1  |
+------+------+
| true | ZSTD |
+------+------+

      • When uncompressed: content_encoding is NULL

      • During compression: content_encoding returns the specific codec name.

    View storage information

    1. Prepare a test table.

      -- Create a table that contains a BLOB column.
CREATE TABLE blob_table2 (
  col1 INT ,
  col2 BLOB
)
TBLPROPERTIES (
  "table.format.version"="2" 
);

-- Write data to the table.
INSERT INTO blob_table2 VALUES (1, to_blob(repeat('aaa', 1000), 'application/json'));

-- Read data from the table.
SELECT col1,read_blob(col2) FROM blob_table2;

    2. View the storage information.

      SELECT
  get_json_object(GET_BLOB_METADATA(col2), '$.storage_type'),
  get_json_object(GET_BLOB_METADATA(col2), '$.blob_storage_tier')
FROM blob_table2;

-- Return value:
+-------+----------+
| _c0   | _c1      |
+-------+----------+
| PANGU | STANDARD |
+-------+----------+

    Usage with other functions

    • Use with to_blob to verify that a created blob contains the expected metadata.

    • Use with LENGTHB to validate that the length in the metadata matches the actual content length in bytes.

    • Use with read_blob; read_blob inspects the content, while GET_BLOB_METADATA inspects its metadata.

    • Use with GET_JSON_OBJECT. This is the most common and recommended usage.