Add EXISTS PATH columns to JSON_TABLE

Author: Nikita Glukhov

doc/src/sgml/func.sgml

@@ -18613,6 +18613,8 @@ where <replaceable class="parameter">json_table_column</replaceable> is:
         [ { KEEP | OMIT } QUOTES [ ON SCALAR STRING ] ]
         [ { ERROR | NULL | EMPTY { ARRAY | OBJECT } } ON EMPTY ]
         [ { ERROR | NULL | EMPTY { ARRAY | OBJECT } } ON ERROR ]
+  | <replaceable>name</replaceable> <replaceable>type</replaceable> EXISTS [ PATH <replaceable>json_path_specification</replaceable> ]
+        [ { ERROR | TRUE | FALSE | UNKNOWN } ON ERROR ]
   | NESTED PATH <replaceable>json_path_specification</replaceable> [ AS <replaceable>path_name</replaceable> ]
         COLUMNS ( <replaceable>json_table_column</replaceable> [, ...] )
   | <replaceable>name</replaceable> FOR ORDINALITY
@@ -18785,6 +18787,38 @@ where <replaceable class="parameter">json_table_column</replaceable> is:
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term>
+     <literal>
+       <replaceable>name</replaceable> <replaceable>type</replaceable>
+       EXISTS [ PATH <replaceable>json_path_specification</replaceable> ]
+     </literal>
+    </term>
+    <listitem>
+
+    <para>
+     Gerenates a column and inserts a boolean item into each row of this column.
+    </para>
+    <para>
+     The provided <literal>PATH</literal> expression parses the
+     row pattern defined by <replaceable>json_api_common_syntax</replaceable>,
+     checks whether any SQL/JSON items were returned, and fills the column with
+     resulting boolean value, one for each row.
+     The specified <replaceable>type</replaceable> should have cast from
+     <type>boolean</type>.
+     If the <literal>PATH</literal> expression is omitted,
+     <function>JSON_TABLE</function> uses the
+     <literal>$.<replaceable>name</replaceable></literal> path expression,
+     where <replaceable>name</replaceable> is the provided column name.
+    </para>
+    <para>
+     Optionally, you can add <literal>ON ERROR</literal> clause to define
+     error behavior.  This clause have the same syntax and semantics as in
+     <xref linkend="functions-jsonexists"/>.
+    </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term>
      <literal>NESTED PATH <replaceable>json_path_specification</replaceable> [ AS <replaceable>json_path_name</replaceable> ]

src/backend/parser/gram.y

@@ -639,6 +639,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 					json_table_ordinality_column_definition
 					json_table_regular_column_definition
 					json_table_formatted_column_definition
+					json_table_exists_column_definition
 					json_table_nested_columns
 
 %type <list>		json_name_and_value_list
@@ -15156,6 +15157,7 @@ json_table_column_definition:
 			json_table_ordinality_column_definition		%prec json_table_column
 			| json_table_regular_column_definition 		%prec json_table_column
 			| json_table_formatted_column_definition	%prec json_table_column
+			| json_table_exists_column_definition		%prec json_table_column
 			| json_table_nested_columns
 		;
 
@@ -15190,6 +15192,26 @@ json_table_regular_column_definition:
 				}
 		;
 
+json_table_exists_column_definition:
+			ColId Typename
+			EXISTS json_table_column_path_specification_clause_opt
+			json_exists_error_clause_opt
+				{
+					JsonTableColumn *n = makeNode(JsonTableColumn);
+					n->coltype = JTC_EXISTS;
+					n->name = $1;
+					n->typeName = $2;
+					n->format = makeJsonFormat(JS_FORMAT_DEFAULT, JS_ENC_DEFAULT, -1);
+					n->wrapper = JSW_NONE;
+					n->omit_quotes = false;
+					n->pathspec = $4;
+					n->on_empty = NULL;
+					n->on_error = $5;
+					n->location = @1;
+					$$ = (Node *) n;
+				}
+		;
+
 json_table_error_behavior:
 			json_behavior_error
 			| json_behavior_empty

src/backend/parser/parse_jsontable.c

@@ -72,7 +72,9 @@ transformJsonTableColumn(JsonTableColumn *jtc, Node *contextItemExpr,
 	JsonPathSpec pathspec;
 	JsonFormat *default_format;
 
-	jfexpr->op = jtc->coltype == JTC_REGULAR ? IS_JSON_VALUE : IS_JSON_QUERY;
+	jfexpr->op =
+		jtc->coltype == JTC_REGULAR ? IS_JSON_VALUE :
+		jtc->coltype == JTC_EXISTS ? IS_JSON_EXISTS : IS_JSON_QUERY;
 	jfexpr->common = common;
 	jfexpr->output = output;
 	jfexpr->on_empty = jtc->on_empty;
@@ -260,6 +262,7 @@ appendJsonTableColumns(JsonTableContext *cxt, List *columns)
 				break;
 
 			case JTC_REGULAR:
+			case JTC_EXISTS:
 			case JTC_FORMATTED:
 				{
 					Node	   *je;

src/backend/utils/adt/ruleutils.c

@@ -10462,6 +10462,7 @@ get_json_table_columns(TableFunc *tf, JsonTableParentNode *node,
 		Oid			typid;
 		int32		typmod;
 		bool		ordinality;
+		JsonBehaviorType default_behavior;
 
 		typid = lfirst_oid(l2);
 		l2 = lnext(tf->coltypes, l2);
@@ -10494,18 +10495,28 @@ get_json_table_columns(TableFunc *tf, JsonTableParentNode *node,
 		if (ordinality)
 			continue;
 
-		if (colexpr->op == IS_JSON_QUERY)
-			appendStringInfoString(buf,
-								   colexpr->format->format == JS_FORMAT_JSONB ?
-								   " FORMAT JSONB" : " FORMAT JSON");
+		if (colexpr->op == IS_JSON_EXISTS)
+		{
+			appendStringInfoString(buf, " EXISTS");
+			default_behavior = JSON_BEHAVIOR_FALSE;
+		}
+		else
+		{
+			if (colexpr->op == IS_JSON_QUERY)
+				appendStringInfoString(buf,
+									   colexpr->format->format == JS_FORMAT_JSONB ?
+									   " FORMAT JSONB" : " FORMAT JSON");
+			default_behavior = JSON_BEHAVIOR_NULL;
+		}
+
+		if (jexpr->on_error->btype == JSON_BEHAVIOR_ERROR)
+			default_behavior = JSON_BEHAVIOR_ERROR;
 
 		appendStringInfoString(buf, " PATH ");
 
 		get_json_path_spec(colexpr->path_spec, context, showimplicit);
 
-		get_json_expr_options(colexpr, context,
-							  jexpr->on_error->btype == JSON_BEHAVIOR_ERROR ?
-							  JSON_BEHAVIOR_ERROR : JSON_BEHAVIOR_NULL);
+		get_json_expr_options(colexpr, context, default_behavior);
 	}
 
 	if (node->child)

src/include/nodes/parsenodes.h

@@ -1507,6 +1507,7 @@ typedef enum
 {
 	JTC_FOR_ORDINALITY,
 	JTC_REGULAR,
+	JTC_EXISTS,
 	JTC_FORMATTED,
 	JTC_NESTED,
 } JsonTableColumnType;