3 files changed, 19 insertions, 0 deletions
diff --git a/includes/database/database.inc b/includes/database/database.inc
index eecb8f88c..043515548 100644
--- a/includes/database/database.inc
+++ b/includes/database/database.inc
@@ -1170,6 +1170,14 @@ abstract class Database {
 class TransactionsNotSupportedException extends PDOException { }
 
 /**
+ * Exception thrown for merge queries that do not make semantic sense.
+ *
+ * There are many ways that a merge query could be malformed.  They should all
+ * throw this exception and set an appropriately descriptive message.
+ */
+class InvalidMergeQueryException extends Exception {}
+
+/**
  * A wrapper class for creating and managing database transactions.
  *
  * Not all databases or database configurations support transactions. For
diff --git a/includes/database/mysql/query.inc b/includes/database/mysql/query.inc
index d48681316..751137602 100644
--- a/includes/database/mysql/query.inc
+++ b/includes/database/mysql/query.inc
@@ -80,6 +80,12 @@ class InsertQuery_mysql extends InsertQuery {
 class MergeQuery_mysql extends MergeQuery {
 
   public function execute() {
+
+    // A merge query without any key field is invalid.
+    if (count($this->keyFields) == 0) {
+      throw new InvalidMergeQueryException("You need to specify key fields before executing a merge query");
+    }
+
     // Set defaults.
     if ($this->updateFields) {
       $update_fields = $this->updateFields;
diff --git a/includes/database/query.inc b/includes/database/query.inc
index 396b59afb..c8e312dec 100644
--- a/includes/database/query.inc
+++ b/includes/database/query.inc
@@ -635,6 +635,11 @@ class MergeQuery extends Query {
 
   public function execute() {
 
+    // A merge query without any key field is invalid.
+    if (count($this->keyFields) == 0) {
+      throw new InvalidMergeQueryException("You need to specify key fields before executing a merge query");
+    }
+
     // In the degenerate case of this query type, we have to run multiple
     // queries as there is no universal single-query mechanism that will work.
     // Our degenerate case is not designed for performance efficiency but