Skip queries which don't touch any rows from anonymization.

Author: cristianberneanu

pg_diffix/query/validation.h

@@ -45,10 +45,4 @@ extern bool is_supported_numeric_type(Oid type);
  */
 extern double numeric_value_to_double(Oid type, Datum value);
 
-/*
- * If argument is a `cast` expression, returns the casted subject node.
- * Otherwise, returns the given argument as is.
- */
-extern Node *unwrap_cast(Node *node);
-
 #endif /* PG_DIFFIX_VALIDATION_H */

src/query/anonymization.c

@@ -620,17 +620,28 @@ static void compile_anonymizing_query(Query *query, List *personal_relations, An
   wrap_having_qual(query);
 }
 
-static bool is_anonymizing_query(Query *query, List *personal_relations)
+static bool are_qualifiers_always_false(Node *quals)
 {
-  if (query->limitCount != NULL)
+  if (quals == NULL)
+    return false;
+
+  if (!IsA(quals, Const))
   {
-    Node *limit = unwrap_cast(query->limitCount);
-    if (IsA(limit, Const) &&
-        ((Const *)limit)->consttype == INT4OID &&
-        DatumGetInt32(((Const *)limit)->constvalue) == 0)
-      return false; /* No need for anonymization if no rows are requested. */
+    quals = eval_const_expressions(NULL, quals);
+    if (!IsA(quals, Const))
+      return false;
   }
 
+  Const *result = (Const *)quals;
+  Assert(result->consttype == BOOLOID);
+  return result->constisnull || DatumGetBool(result->constvalue) == false;
+}
+
+static bool is_anonymizing_query(Query *query, List *personal_relations)
+{
+  if (are_qualifiers_always_false(query->jointree->quals))
+    return false; /* No need for anonymization if no rows will be processed. */
+
   ListCell *cell;
   foreach (cell, query->rtable)
   {

src/query/validation.c

@@ -138,7 +138,7 @@ static bool is_datetime_to_string_cast(CoerceViaIO *expr)
   return TypeCategory(exprType(arg)) == TYPCATEGORY_DATETIME && TypeCategory(expr->resulttype) == TYPCATEGORY_STRING;
 }
 
-Node *unwrap_cast(Node *node)
+static Node *unwrap_cast(Node *node)
 {
   if (IsA(node, FuncExpr))
   {

test/expected/misc.out

@@ -197,3 +197,18 @@ EXPLAIN SELECT city FROM test_customers ORDER BY 1;
                ->  Seq Scan on test_customers
 (6 rows)
 
+-- Allow queries that exclude all rows
+SELECT FROM test_customers WHERE FALSE;
+--
+(0 rows)
+
+SELECT TRUE AS "_" FROM test_customers WHERE 1 <> 1 LIMIT 0;
+ _ 
+---
+(0 rows)
+
+SELECT id FROM test_customers WHERE NULL = NULL;
+ id 
+----
+(0 rows)
+

test/sql/misc.sql

@@ -95,3 +95,8 @@ EXPLAIN (ANALYZE, SUMMARY false, TIMING false, COSTS true) SELECT name FROM test
 
 -- EXPLAIN prints group/sort names
 EXPLAIN SELECT city FROM test_customers ORDER BY 1;
+
+-- Allow queries that exclude all rows
+SELECT FROM test_customers WHERE FALSE;
+SELECT TRUE AS "_" FROM test_customers WHERE 1 <> 1 LIMIT 0;
+SELECT id FROM test_customers WHERE NULL = NULL;