Merge pull request #429 from diffix/cristian/misc

Skip queries with no rows from anonymization.

Author: cristianberneanu

src/query/anonymization.c

@@ -620,8 +620,28 @@ static void compile_anonymizing_query(Query *query, List *personal_relations, An
   wrap_having_qual(query);
 }
 
+static bool are_qualifiers_always_false(Node *quals)
+{
+  if (quals == NULL)
+    return false;
+
+  if (!IsA(quals, Const))
+  {
+    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)
   {
@@ -633,6 +653,7 @@ static bool is_anonymizing_query(Query *query, List *personal_relations)
         return true;
     }
   }
+
   return false;
 }
 

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;