JSON_ARRAY_UNPACK
Converts an encoded blob representing a vector to a JSON array representing the same vector.
It is a scalar function.
Syntax
JSON_ARRAY_UNPACK(vector_expression)
Arguments
vector_expression: An expression that evaluates to a vector. The vector must be encoded as a blob containing packed single-precision or double-precision floating-point numbers in little-endian byte order.
Return Type
A JSON array of zero or more floating point numbers.
Remarks
A vector can be of any length, but blob lengths must be divisible by 4 bytes (or 8 bytes, depending on the datatype specified).
You can specify the datatype of the vector elements in which this operation is performed on the vector by adding a suffix to the function. Omitting the suffix from the function is equivalent to suffixing it with _F32. All operations are done using the specified datatype. The following table lists the suffixes and their datatype.
Suffix | Datatype |
|---|---|
| 8-bit signed integer |
| 16-bit signed integer |
| 32-bit signed integer |
| 64-bit signed integer |
| 32-bit floating-point number (IEEE standard format) |
| 64-bit floating-point number (IEEE standard format) |
Examples
The following examples use the ju_t table.
CREATE TABLE ju_t (x BLOB, y BLOB);
INSERT INTO ju_t VALUES (JSON_ARRAY_PACK('[12.1, 6.4]'), JSON_ARRAY_PACK('[8.6,9.2]'));
INSERT INTO ju_t VALUES (JSON_ARRAY_PACK('[5.2, 11.7]'), JSON_ARRAY_PACK('[4.6,7.3]'));Querying Rows Using JSON_ARRAY_UNPACK
The following example queries the t table using the JSON_ARRAY_UNPACK() function:
SELECT JSON_ARRAY_UNPACK(x) "x", JSON_ARRAY_UNPACK(y) "y" from ju_t; **** +-------------------------+-------------------------+ | x | y | +-------------------------+-------------------------+ | [12.1000004,6.4000001] | [8.60000038,9.19999981] | | [5.19999981,11.6999998] | [4.5999999,7.30000019] | +-------------------------+-------------------------+
Typecasting the Datatype using Suffixes
The values inserted in the t table are 32-bit floating point numbers, because no suffix was specified with the JSON_ARRAY_PACK() function. The following query returns the vector blobs as 32-bit integers.
SELECT JSON_ARRAY_UNPACK_I32(x) "x", JSON_ARRAY_UNPACK_I32(y) "y" from ju_t; **** +-------------------------+-------------------------+ | x | y | +-------------------------+-------------------------+ | [1094818202,1087163597] | [1091148186,1091777331] | | [1084647014,1094398771] | [1083388723,1089051034] | +-------------------------+-------------------------+