Enable DEFAULT behavior for JSON_QUERY

Author: Nikita Glukhov

doc/src/sgml/func.sgml

@@ -18005,8 +18005,8 @@ SELECT JSON_VALUE(jsonb '[1,2]', 'strict $[*]' DEFAULT 1 ON ERROR);
   [ RETURNING <replaceable class="parameter">data_type</replaceable> [ FORMAT JSON [ ENCODING UTF8 ] ]
   [ { WITHOUT | WITH { CONDITIONAL | [UNCONDITIONAL] } } [ ARRAY ] WRAPPER ]
   [ { KEEP | OMIT } QUOTES [ ON SCALAR STRING ] ]
-  [ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } } ON EMPTY ]
-  [ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } } ON ERROR ]
+  [ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT <replaceable class="parameter">expression</replaceable> } ON EMPTY ]
+  [ { ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT <replaceable class="parameter">expression</replaceable> } ON ERROR ]
 )
   </synopsis>
     </refsynopsisdiv>
@@ -18120,13 +18120,16 @@ SELECT JSON_VALUE(jsonb '[1,2]', 'strict $[*]' DEFAULT 1 ON ERROR);
 
   <varlistentry>
     <term>
-     <literal>{ ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } } ON EMPTY</literal>
+     <literal>{ ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT <replaceable class="parameter">expression</replaceable> } ON EMPTY</literal>
     </term>
     <listitem>
      <para>
        Defines the return value if no JSON value is found. The default is <literal>NULL</literal>.
        If you use <literal>EMPTY [ARRAY]</literal> or <literal>EMPTY OBJECT</literal>,
        an empty JSON array [] or object {} is returned, respectively.
+       If you use <literal>DEFAULT <replaceable>expression</replaceable></literal>,
+       the provided <replaceable>expression</replaceable> is evaluated and cast
+       to the type specified in the <command>RETURNING</command> clause.
      </para>
      <para>
        You cannot use this clause together with the <literal>WRAPPER</literal> clause.
@@ -18136,13 +18139,16 @@ SELECT JSON_VALUE(jsonb '[1,2]', 'strict $[*]' DEFAULT 1 ON ERROR);
 
      <varlistentry>
     <term>
-     <literal>{ ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } } ON ERROR</literal>
+     <literal>{ ERROR | NULL | EMPTY { [ ARRAY ] | OBJECT } | DEFAULT <replaceable class="parameter">expression</replaceable> } ON ERROR</literal>
     </term>
     <listitem>
      <para>
        Defines the return value if an unhandled error occurs. The default is <literal>NULL</literal>.
        If you use <literal>EMPTY [ARRAY]</literal> or <literal>EMPTY OBJECT</literal>,
        an empty JSON array [] or object {} are returned, respectively.
+       If you use <literal>DEFAULT <replaceable>expression</replaceable></literal>,
+       the provided <replaceable>expression</replaceable> is evaluated and cast
+       to the type specified in the <command>RETURNING</command> clause.
      </para>
      </listitem>
    </varlistentry>

src/backend/parser/gram.y

@@ -15020,6 +15020,7 @@ json_query_behavior:
 			| json_behavior_null
 			| json_behavior_empty_array
 			| json_behavior_empty_object
+			| json_behavior_default
 		;
 
 json_query_on_behavior_clause_opt:

src/backend/parser/parse_expr.c

@@ -4820,6 +4820,14 @@ transformJsonFuncExpr(ParseState *pstate, JsonFuncExpr *func)
 
 			transformJsonFuncExprOutput(pstate, func, jsexpr);
 
+			jsexpr->on_empty->default_expr =
+				coerceDefaultJsonExpr(pstate, jsexpr,
+									  jsexpr->on_empty->default_expr);
+
+			jsexpr->on_error->default_expr =
+				coerceDefaultJsonExpr(pstate, jsexpr,
+									  jsexpr->on_error->default_expr);
+
 			jsexpr->wrapper = func->wrapper;
 			jsexpr->omit_quotes = func->omit_quotes;
 

src/test/regress/expected/jsonb_sqljson.out

@@ -682,6 +682,12 @@ SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY);
 
 (1 row)
 
+SELECT JSON_QUERY(jsonb '[]', '$[*]' DEFAULT '"empty"' ON EMPTY);
+ json_query 
+------------
+ "empty"
+(1 row)
+
 SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY NULL ON ERROR);
  json_query 
 ------------
@@ -711,6 +717,12 @@ SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON ERROR);
 SELECT JSON_QUERY(jsonb '[1,2]', '$[*]' ERROR ON ERROR);
 ERROR:  JSON path expression in JSON_QUERY should return singleton item without wrapper
 HINT:  use WITH WRAPPER clause to wrap SQL/JSON item sequence into array
+SELECT JSON_QUERY(jsonb '[1,2]', '$[*]' DEFAULT '"empty"' ON ERROR);
+ json_query 
+------------
+ "empty"
+(1 row)
+
 SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING json);
  json_query 
 ------------

src/test/regress/sql/jsonb_sqljson.sql

@@ -195,6 +195,7 @@ SELECT JSON_QUERY(jsonb '[]', '$[*]' EMPTY ON EMPTY);
 SELECT JSON_QUERY(jsonb '[]', '$[*]' EMPTY ARRAY ON EMPTY);
 SELECT JSON_QUERY(jsonb '[]', '$[*]' EMPTY OBJECT ON EMPTY);
 SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY);
+SELECT JSON_QUERY(jsonb '[]', '$[*]' DEFAULT '"empty"' ON EMPTY);
 
 SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY NULL ON ERROR);
 SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY EMPTY ARRAY ON ERROR);
@@ -203,6 +204,7 @@ SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON EMPTY ERROR ON ERROR);
 SELECT JSON_QUERY(jsonb '[]', '$[*]' ERROR ON ERROR);
 
 SELECT JSON_QUERY(jsonb '[1,2]', '$[*]' ERROR ON ERROR);
+SELECT JSON_QUERY(jsonb '[1,2]', '$[*]' DEFAULT '"empty"' ON ERROR);
 
 SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING json);
 SELECT JSON_QUERY(jsonb '[1,2]', '$' RETURNING json FORMAT JSON);