#754743 : throw IllegalStateException on multiple usage of sources

querydsl-sql/src/test/java/com/mysema/query/sql/JoinUsageTest.java

@@ -0,0 +1,15 @@
+package com.mysema.query.sql;
+
+import org.junit.Test;
+
+import com.mysema.query.sql.domain.QSurvey;
+
+public class JoinUsageTest {
+    
+    @Test(expected=IllegalStateException.class)
+    public void Join_Already_Declared(){
+        SQLSubQuery subQuery = new SQLSubQuery();
+        subQuery.from(QSurvey.survey).fullJoin(QSurvey.survey);
+    }
+
+}