15 SQL/JSON Condition JSON_EXISTS
SQL/JSON condition json_exists
lets you use a SQL/JSON
path expression as a row filter, to select rows based on the content of JSON documents. You
can use condition json_exists
in a CASE
expression or the
WHERE
clause of a SELECT
statement.
Condition json_exists
checks for the existence of a
particular value within JSON data: it returns true if the value is present and false
if it is absent. More precisely, json_exists
returns true if the
data it targets matches one or more JSON values. If no JSON values are matched then
it returns false.
You can also use json_exists
to create bitmap indexes for use with JSON data — see Example 26-1.
Error handlers
ERROR ON ERROR
, FALSE ON ERROR
, and
TRUE ON ERROR
apply. The default is FALSE ON
ERROR
. The handler takes effect when any error occurs, but typically an
error occurs when the given JSON data is not well-formed (using lax syntax). Unlike
the case for conditions is json
and is not json
,
condition json_exists
expects the data it examines to be well-formed JSON data.
The second argument to json_exists
is a SQL/JSON path expression
followed by an optional PASSING
clause and an optional error
clause.
The optional filter expression of a SQL/JSON path
expression used with json_exists
can refer to SQL/JSON variables,
whose values are passed from SQL by binding them with the PASSING
clause. The following SQL data types are supported for such variables:
VARCHAR2
, NUMBER
,
BINARY_DOUBLE
, DATE
,
TIMESTAMP
, and TIMESTAMP WITH
TIMEZONE
.
Note:
SQL/JSON condition json_exists
applied to JSON
value null
returns the SQL string
'true'
.
See Also:
Oracle Database SQL Language Reference for information about
json_exists
- Using Filters with JSON_EXISTS
You can use SQL/JSON conditionjson_exists
with a path expression that has one or more filter expressions, to select documents that contain matching data. Filters let you test for the existence of documents that have particular fields that satisfy various conditions. - JSON_EXISTS as JSON_TABLE
SQL/JSON conditionjson_exists
can be viewed as a special case of SQL/JSON functionjson_table
.
Related Topics
Parent topic: Query JSON Data
15.1 Using Filters with JSON_EXISTS
You can use SQL/JSON condition json_exists
with a path
expression that has one or more filter expressions, to select documents that contain matching
data. Filters let you test for the existence of documents that have particular fields that
satisfy various conditions.
SQL/JSON
condition json_exists
returns true for documents containing data that
matches a SQL/JSON path expression. If the path expression contains a filter, then the data
that matches the path to which that filter is applied must also satisfy the filter, in order
for json_exists
to return true for the document containing the data.
A filter applies to the path that immediately precedes it, and the test is
whether both (a) the given document has some data that matches that path, and (b) that
matching data satisfies the filter. If both of these conditions hold then
json_exists
returns true for the document.
The path
expression immediately preceding a filter defines the scope of the patterns used in it. An
at-sign (@
) within a filter refers to the data targeted by that
path, which is termed the current item for the filter. For example, in the path
expression $.LineItems?(@.Part.UPCCode == 85391628927)
, @
refers to an occurrence of array LineItems
.
Example 15-1 JSON_EXISTS: Path Expression Without Filter
This example selects purchase-order documents that have a line item whose part description contains a UPC code entry.
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$.LineItems.Part.UPCCode');
Example 15-2 JSON_EXISTS: Current Item and Scope in Path Expression Filters
This example shows three equivalent ways to
select documents that have a line item whose part contains a UPC code with a value of
85391628927
.
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$?(@.LineItems.Part.UPCCode == 85391628927)');
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$.LineItems?(@.Part.UPCCode == 85391628927)');
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$.LineItems.Part?(@.UPCCode == 85391628927)');
-
In the first query, the scope of the filter is the context item, that is, an entire purchase order.
@
refers to the context item. -
In the second query, the filter scope is a
LineItems
array (and each of its elements, implicitly).@
refers to an element of that array. -
In the third query, the filter scope is a
Part
field of an element in aLineItems
array.@
refers to aPart
field.
Example 15-3 JSON_EXISTS: Filter Conditions Depend On the Current Item
This example selects purchase-order documents that have
both a line item with a part that has UPC code 85391628927
and a line item with an order quantity greater than 3. The scope of each filter, that
is, the current item, is in this case the context item. Each filter condition applies
independently (to the same document); the two conditions do not necessarily apply to
the same line
item.
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$?(@.LineItems.Part.UPCCode == 85391628927
&& @.LineItems.Quantity > 3)');
Example 15-4 JSON_EXISTS: Filter Downscoping
This example looks similar to Example 15-3, but it acts quite differently. It selects purchase-order
documents that have a line item with a part that has UPC code and with an order
quantity greater than 3. The scope of the current item in the filter is at a lower level; it
is not the context item but a LineItems
array element. That is, the same
line item must satisfy both conditions, for json_exists
to return
true.
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document, '$.LineItems?(@.Part.UPCCode == 85391628927
&& @.Quantity > 3)');
Example 15-5 JSON_EXISTS: Path Expression Using Path-Expression exists Condition
This example shows how to downscope
one part of a filter while leaving another part scoped at the document (context-item) level.
It selects purchase-order documents that have a User
field whose value is
"ABULL"
and documents that have a line item with a part that has UPC code
and with an order quantity greater than 3. That is, it selects the same documents
selected by Example 15-4, as well as all documents that have
"ABULL"
as the user. The argument to path-expression predicate
exists
is a path expression that specifies particular line
items; the predicate returns true if a match is found, that is, if any such line items
exist.
(If you use this example or similar with SQL*Plus then you must
use SET DEFINE OFF
first, so that SQL*Plus does not interpret
&& exists
as a substitution variable and prompt you to define
it.)
SELECT po.po_document FROM j_purchaseorder po
WHERE json_exists(po.po_document,
'$?(@.User == "ABULL"
&& exists(@.LineItems?(@.Part.UPCCode == 85391628927
&& @.Quantity > 3)))');
Related Topics
Parent topic: SQL/JSON Condition JSON_EXISTS
15.2 JSON_EXISTS as JSON_TABLE
SQL/JSON condition json_exists
can be viewed as a special case of SQL/JSON function json_table
.
Example 15-6 illustrates the equivalence: the two SELECT
statements have the same effect.
In addition to perhaps helping you understand json_exists
better, this equivalence is important practically, because it means that you can use either to get the same effect.
In particular, if you use json_exists
more than once, or you use it in combination with json_value
or json_query
(which can also be expressed using json_table
), to access the same data, then a single invocation of json_table
presents the advantage that the data is parsed only once.
Because of this, the optimizer often automatically rewrites multiple invocations of json_exists
, json_value
and json_query
(any combination) to fewer invocations of json_table
.
Example 15-6 JSON_EXISTS Expressed Using JSON_TABLE
SELECT select_list
FROM table WHERE json_exists(column, json_path error_handler ON ERROR);
SELECT select_list
FROM table,
json_table(column, '$' error_handler ON ERROR
COLUMNS ("COLUMN_ALIAS" NUMBER EXISTS PATH json_path)) AS "JT"
WHERE jt.column_alias = 1;
Parent topic: SQL/JSON Condition JSON_EXISTS