90 DBMS_JSON
The DBMS_JSON
package provides an interface for data-guide operations.
This chapter contains the following topics:
90.1 DBMS_JSON Overview
Package DBMS_JSON
provides subprograms for manipulating JavaScript Object Notation (JSON) data that is stored in Oracle Database.
90.2 DBMS_JSON Security Model
PUBLIC
is granted the EXECUTE
privilege on package DBMS_JSON
. Its subprograms execute with invoker's rights privileges.
90.3 DBMS_JSON Constants
The DBMS_JSON package uses these constants to define the JSON schema types and data-guide formatting options.
Table 90-1 DBMS_JSON Constants Defined for JSON Data-Guide Formatting
Name | Value | Description |
---|---|---|
FORMAT_FLAT | 2 | Display flat format |
FORMAT_HIERARCHICAL | 1 | Display hierarchical format |
PRETTY | 1 | Use appropriate indention to improve readability |
Table 90-2 DBMS_JSON Constants for JSON Schema Types
Name | Type | Value | Description |
---|---|---|---|
TYPE_ARRAY | NUMBER(2) | 6 | A JSON array |
TYPE_BOOLEAN | NUMBER(2) | 2 | A JSON boolean |
TYPE_OBJECT | NUMBER(2) | 5 | A JSON object |
TYPE_NULL | NUMBER(2) | 1 | The JSON NULL value |
TYPE_NUMBER | NUMBER(2) | 3 | A JSON number |
TYPE_STRING | NUMBER(2) | 4 | A JSON string |
90.4 Summary of DBMS_JSON Subprograms
This table lists the DBMS_JSON
subprograms and briefly describes them.
DBMS_JSON Package Subprograms
Subprogram | Description |
---|---|
ADD_VIRTUAL_COLUMNS Procedure |
Add virtual columns based on data-guide information. This has no effect when running on the shard catalog server — no virtual column is added. |
CREATE_VIEW Procedure | Create a view with relational columns and scalar JSON fields as specified in a data guide. |
CREATE_VIEW_ON_PATH Procedure |
Create a view based on data-guide information, with relational columns, top-level scalar types, and fully expanded sub-tree under a given path. When running on the shard catalog server this raises an error stating that the data guide is empty. |
DROP_VIRTUAL_COLUMNS Procedure |
Drop virtual columns created by procedure This has no effect when running on the shard catalog server. |
GET_INDEX_DATAGUIDE Function |
Get JSON data guide from a data guide-enabled JSON search index. When running on the shard catalog server this returns a single empty row as result. |
RENAME_COLUMN Procedure |
Set the preferred name for a view column or a virtual column creating using a data guide. This has no effect when running on the shard catalog server. |
Note:
In the context of sharding, each individual shard maintains its own data-guide information, which is obtained from the JSON documents stored in that shard. When running on individual shard, procedures in this package that use data-guide information use only the information that is maintained for that shard.
90.4.1 ADD_VIRTUAL_COLUMNS Procedure
This procedure adds virtual columns based on the data guide.
The virtual column name is the value of o:preferred_vc_name
in the data guide. The procedure ignores JSON objects, arrays, and fields under arrays in the data guide. Before it adds virtual columns, procedure add_virtual_columns
first drops any existing virtual columns that were projected from fields in the same JSON column by a previous invocation of add_virtual_columns
or by data-guide change-trigger procedure add_vc
(in effect, it does what procedure DBMS_JSON.drop_virtual_columns
does).
Syntax
DBMS_JSON.ADD_VIRTUAL_COLUMNS (
tablename IN VARCHAR2,
jcolname IN VARCHAR2,
dataguide IN CLOB);
For the following signature you must have a data guide-enabled search index on the JSON column. (This is not needed for the previous signature.)
DBMS_JSON.ADD_VIRTUAL_COLUMNS (
tablename IN VARCHAR2,
jcolname IN VARCHAR2,
frequency NUMBER DEFAULT 0,
hidden BOOLEAN DEFAULT FALSE);
Parameters
Table 90-3 ADD_VIRTUAL_COLUMNS Procedure Parameters
Parameter | Description |
---|---|
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename that contains the data from which to create the virtual column.
|
frequency |
Sets the minimum frequency threshold to display JSON columns. A frequency of 0 means display all JSON columns. Also, all JSON columns are displayed if statistics have not been collected, effectively overriding any value set by this parameter. |
hidden |
TRUE means the added virtual column is hidden; FALSE means it is not. The default is FALSE .
|
dataguide |
The data guide. When o:hidden in the data guide for a particular JSON field is set to TRUE , the corresponding virtual column is added as a hidden column. The default value of o:hidden is FALSE .
|
Usage Notes
Procedure DBMS_STATS.GATHER_STATS
collects statistics in the data guide. If the frequency statistic has not been collected, frequency is NULL
. Setting the frequency to a value greater than zero means do not include columns for which there are no frequency statistics collected (statistic is NULL
), unless DBMS_STATS.GATHER_STATS
has never been executed. In that case, the frequency parameter is ignored and all columns are displayed in the view.
90.4.2 CREATE_VIEW Procedure
This procedure creates a view with relational columns, using scalar JSON fields as specified in the data guide. A data guide-enabled JSON search index is not required for this procedure; the data guide is passed to the procedure.
See Also:
Syntax
(Optional) Enter syntax information here.
PROCEDURE CREATE_VIEW (
viewname VARCHAR2,
tablename VARCHAR2,
jcolname VARCHAR2,
dataguide CLOB);
Parameters
Table 90-4 DBMS_JSON.CREATE_VIEW Procedure Parameters
Parameter | Description |
---|---|
viewname |
Name of the view. |
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename that is used to create the view.
|
dataguide |
The data guide. |
90.4.3 CREATE_VIEW_ON_PATH Procedure
This procedure creates a view with relational columns, using top-level scalar values and the scalar values in the expanded sub-tree under a given path. The JSON column must have a data guide-enabled search index.
See Also:
Syntax
PROCEDURE CREATE_VIEW_ON_PATH(
viewname VARCHAR2,
tablename VARCHAR2,
jcolname VARCHAR2,
path VARCHAR2,
frequency NUMBER DEFAULT 0);
Parameters
Table 90-5 CREATE_VIEW_ON_PATH Procedure Parameters
Parameter | Description |
---|---|
viewname |
Name of the view. |
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename that is used to create the view. The column must have a data guide-enabled JSON search index, or else an error is raised.
|
path |
The path of the JSON field to be expanded. It uses JSON path-expression syntax. It expands the descendants under the specified path, and creates view columns for each scalar value in the resulting sub-tree. The path $ creates a view starting from the JSON document root.
|
frequency |
The minimum frequency threshold for displaying the JSON columns. A frequency of 0 means display all JSON columns. All JSON columns are also displayed if statistics have not been collected, effectively overriding any value set by this parameter. The view only displays JSON fields with frequency greater than the given frequency . It does not display JSON fields added after collecting statistics if the given frequency is greater than 0, if their statistic columns are NULL .
|
90.4.4 DROP_VIRTUAL_COLUMNS Procedure
Drop all virtual columns that were added using PL/SQL procedure DBMS_JSON.add_virtual_columns
or using data-guide change-trigger procedure add_vc
.
Syntax
PROCEDURE DROP_VIRTUAL_COLUMNS(
tablename VARCHAR2,
jcolname VARCHAR2);
Parameters
Table 90-6 DBMS_JSON.DROP_VIRTUAL_COLUMNS Procedure Parameters
Parameter | Description |
---|---|
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename .
|
90.4.5 GET_INDEX_DATAGUIDE Function
GET_INDEX_DATAGUIDE
gets JSON data guide from data guide-enabled JSON search index.
See Also:
Syntax
FUNCTION GET_INDEX_DATAGUIDE(
tablename VARCHAR2,
jcolname VARCHAR2,
format NUMBER,
pretty NUMBER DEFAULT 0)
RETURN CLOB;
Parameters
Table 90-7 DBMS_JSON.GET_INDEX_DATAGUIDE Procedure Parameters
Parameter | Description |
---|---|
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename that has a data guide-enabled JSON search index.
|
format |
The data-guide format:
|
pretty |
A value of DBMS_JSON.PRETTY means pretty-print the data guide, using indention to improve readability.
|
Example 90-1 Example Get Data Guide in Hierarchical Pretty Format
This example returns the data guide in hierarchical format.
SELECT DBMS_JSON.GET_INDEX_DATAGUIDE(‘T1’, ‘PO’, DBMS_JSON.FORMAT_HIERARCHICAL, DBMS_JSON.PRETTY)
FROM DUAL;
90.4.6 RENAME_COLUMN Procedure
This procedure sets the preferred name for a JSON column, to be used by the create view, or add virtual columns procedure.
See Also:
Syntax
PROCEDURE RENAME_COLUMN(
tablename VARCHAR2,
jcolname VARCHAR2,
path VARCHAR2,
type NUMBER,
preferred_name VARCHAR2);
Parameters
Table 90-8 RENAME_COLUMN Procedure Parameters
Parameter | Description |
---|---|
tablename |
Name of the table containing JSON column jcolname .
|
jcolname |
Name of the JSON column in table tablename . It must have a data guide-enabled JSON search index, or else an error is raised.
|
path |
Path to the JSON field on which to set the preferred column name. |
type |
The type of the JSON field targeted by path . Two JSON fields can have the same path if they are of different types. Possible values:
|
preferred_name |
Preferred name for the JSON field specified by path . If there is a name conflict, a system generated name is used instead.
|
Example 90-2 Example Renaming a Column
This example renames a field to item_name.
EXEC DBMS_JSON.RENAME_COLUMN(‘T1’, ‘PO’, ‘$.purchaseOrder.items.name’, DBMS_JSON.TYPE_STRING, ‘item_name’);