Added custom sql for Oracle index

modules/activiti-engine/src/main/resources/org/activiti/db/liquibase/activiti-5.7.xml

@@ -85,12 +85,21 @@
         <preConditions onFail="MARK_RAN">
             <not>
                 <dbms type="mssql"/>
+                <dbms type="oracle"/>
             </not>
         </preConditions>
         <addUniqueConstraint constraintName="ACT_UNIQ_RU_BUS_KEY"
                              tableName="ACT_RU_EXECUTION"
                              columnNames="PROC_DEF_ID_, BUSINESS_KEY_"/>
-    </changeSet>               
+    </changeSet>
+    
+    <changeSet id="4.2 ACT_UNIQ_RU_BUS_KEY" author="trademakers" dbms="oracle">
+      <sql splitStatements="false">
+        create unique index ACT_UNIQ_RU_BUS_KEY on ACT_RU_EXECUTION
+         (case when BUSINESS_KEY_ is null then null else PROC_DEF_ID_ end,
+          case when BUSINESS_KEY_ is null then null else BUSINESS_KEY_ end);
+      </sql>
+    </changeSet>              
  
     <changeSet id="5 ACT_RU_JOB" author="mmueller">
         <createTable tableName="ACT_RU_JOB">