snuyanzin commented on code in PR #28688:
URL: https://github.com/apache/flink/pull/28688#discussion_r3632395776
##########
flink-table/flink-table-api-java/src/main/java/org/apache/flink/table/api/internal/BaseExpressions.java:
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@@ -2525,6 +2525,82 @@ public OutType jsonQuery(String path, JsonQueryWrapper
wrappingBehavior) {
path, wrappingBehavior, JsonQueryOnEmptyOrError.NULL,
JsonQueryOnEmptyOrError.NULL);
}
+ public OutType jsonLength() {
+ return toApiSpecificExpression(unresolvedCall(JSON_LENGTH, toExpr()));
+ }
+
+ /**
+ * Returns the number of elements in a JSON document, or the length of the
value at the
+ * specified path if one is provided.
+ *
+ * <p>Returns {@code NULL} if the argument is {@code NULL}, the input is
not valid JSON, or the
+ * path does not locate a value.
+ *
+ * <p>The length is determined as follows:
+ *
+ * <ul>
+ * <li>Scalar values (number, string, boolean) have length 1.
+ * <li>Arrays have a length equal to the number of their elements.
+ * <li>Objects have a length equal to the number of their key-value
pairs.
+ * </ul>
+ *
+ * <p>For the path argument, use the form:
+ *
+ * <pre>{@code
+ * path ::= '$' ( '.' <field> | '[' <index> ']' )*
+ * field ::= a key in a JSON object
+ * index ::= a zero-based position in a JSON array
+ * }</pre>
+ *
+ * <p>When provided with a path that uses a wildcard and resolves to 2 or
more paths, {@code
+ * JSON_LENGTH} resolves to {@code NULL}.
+ *
+ * <p>JSON_LENGTH also supports input of the VARIANT type; you can pass
the output of
+ * PARSE_JSON into JSON_LENGTH.
+ *
+ * <p>Because a {@code NULL} result can mean several different things (the
input is not valid
+ * JSON, the path does not match anything, or a wildcard path matched 2 or
more nodes), it is
+ * recommended to pair {@code JSON_LENGTH} with a helper function so
invalid input is handled
+ * explicitly rather than silently returning {@code NULL}:
+ *
+ * <ul>
+ * <li>Without a path, guard the call with {@code IS JSON} to separate
malformed input from a
+ * real result.
+ * <li>With a path, use {@code JSON_EXISTS} to tell "the path is absent"
apart from "the path
+ * matched but was ambiguous / matched 2 or more nodes".
+ * </ul>
+ *
+ * <pre>{@code
+ * // returns the length only for valid JSON, otherwise NULL means
"invalid input"
+ * lit("[1,2,3]").isJson().then(lit("[1,2,3]").jsonLength(),
nullOf(DataTypes.INT()))
+ *
+ * // pathPresent is true even when jsonLength is NULL because of a
multi-match wildcard
+ * lit("{}").jsonExists("$.items[*]")
+ * lit("{}").jsonLength("$.items[*]")
+ * }</pre>
+ *
+ * <p>Examples:
+ *
+ * <pre>{@code
+ * JSON_LENGTH('{"1": "hello", "2": "bye bye"}') // 2
+ * JSON_LENGTH('[1,2,3,4,5]') // 5
+ * JSON_LENGTH('"hello"') // 1
+ *
+ * JSON_LENGTH('{"1": "hello", "2": "bye bye"}', '$.1') // 1
+ * JSON_LENGTH('{"1": [1,2,3], "2": "bye bye"}', '$.1') // 3
+ * JSON_LENGTH('[1,2,3,4,5]', '$[3]') // 1
+ *
+ * JSON_LENGTH('[1,2,3,4,5]', '$.[7]') // Null
Review Comment:
```suggestion
* JSON_LENGTH('[1,2,3,4,5]', '$[7]') // Null
```
is it a typo here?
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