MSSQL script update (#4243)

activiti-core/activiti-engine/src/main/resources/org/activiti/db/upgrade/activiti.mssql.upgradestep.6001.to.6002.engine.sql

@@ -212,4 +212,10 @@ alter table ACT_RU_EXECUTION add ID_LINK_COUNT_ int;
 
 update ACT_GE_PROPERTY set VALUE_ = '6.0.0.2' where NAME_ = 'schema.version';
 
-update ACT_RU_EXECUTION as exe set START_USER_ID_ = (select START_USER_ID_ from ACT_HI_PROCINST where PROC_INST_ID_=exe.PROC_INST_ID_);
+UPDATE outerTable
+SET START_USER_ID_ = innerTable.START_USER_ID_
+    FROM ACT_RU_EXECUTION outerTable
+INNER JOIN
+(
+     select START_USER_ID_, PROC_INST_ID_ from ACT_HI_PROCINST
+) innerTable ON outerTable.PROC_INST_ID_ = innerTable.PROC_INST_ID_;