MCOL-4617 Move in-to-exists predicate creation and injection into the engine.

We earlier leveraged the server functionality provided by

Item_in_subselect::create_in_to_exists_cond and
Item_in_subselect::inject_in_to_exists_cond

to create and inject the in-to-exists predicate into an IN
subquery's JOIN struct. With this patch, we leave the IN subquery's
JOIN unaltered and instead directly perform this predicate creation
and injection into ColumnStore's select execution plan.

dbcon/mysql/ha_mcs_impl_if.h

@@ -158,6 +158,12 @@ struct gp_walk_info
 
     bool isGroupByHandler;
 
+    // MCOL-4617 The below 2 fields are used for in-to-exists
+    // predicate creation and injection. See usage in InSub::transform()
+    // and buildInToExistsFilter()
+    execplan::ReturnedColumn* inSubQueryLHS;
+    Item* inSubQueryLHSItem;
+
     gp_walk_info() : sessionid(0),
         fatalParseError(false),
         condPush(false),
@@ -177,7 +183,9 @@ struct gp_walk_info
         inCaseStmt(false),
         cs_vtable_is_update_with_derive(false),
         cs_vtable_impossible_where_on_union(false),
-        isGroupByHandler(false)
+        isGroupByHandler(false),
+        inSubQueryLHS(nullptr),
+        inSubQueryLHSItem(nullptr)
     {}
 
     ~gp_walk_info() {}
@@ -385,6 +393,13 @@ execplan::ParseTree* setDerivedFilter(THD* thd, execplan::ParseTree*& n,
                                       std::map<std::string, execplan::ParseTree*>& obj,
                                       execplan::CalpontSelectExecutionPlan::SelectList& derivedTbList);
 void derivedTableOptimization(THD* thd, execplan::SCSEP& csep);
+bool buildEqualityPredicate(execplan::ReturnedColumn* lhs,
+    execplan::ReturnedColumn* rhs,
+    gp_walk_info* gwip,
+    boost::shared_ptr<execplan::Operator>& sop,
+    const Item_func::Functype& funcType,
+    const std::vector<Item*>& itemList,
+    bool isInSubs = false);
 
 #ifdef DEBUG_WALK_COND
 void debug_walk(const Item* item, void* arg);