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From GitBox <...@apache.org>
Subject [GitHub] [phoenix] comnetwork commented on a change in pull request #444: PHOENIX-5148
Date Fri, 15 Mar 2019 15:54:48 GMT
comnetwork commented on a change in pull request #444: PHOENIX-5148
URL: https://github.com/apache/phoenix/pull/444#discussion_r266027910
 
 

 ##########
 File path: phoenix-core/src/it/java/org/apache/phoenix/end2end/join/SubqueryUsingSortMergeJoinIT.java
 ##########
 @@ -516,8 +516,8 @@ public void testAnyAllComparisonSubquery() throws Exception {
             assertEquals(rs.getString(2), "T6");
 
             assertFalse(rs.next());
-            
-            query = "SELECT /*+ USE_SORT_MERGE_JOIN*/ \"order_id\", name FROM " + tableName4
+ " o JOIN " + tableName1 + " i ON o.\"item_id\" = i.\"item_id\" WHERE quantity != ANY(SELECT
quantity FROM " + tableName4 + " q WHERE o.\"item_id\" = q.\"item_id\" GROUP BY quantity)";
+            //add order by to make the query result stable
+            query = "SELECT /*+ USE_SORT_MERGE_JOIN*/ \"order_id\", name FROM " + tableName4
+ " o JOIN " + tableName1 + " i ON o.\"item_id\" = i.\"item_id\" WHERE quantity != ANY(SELECT
quantity FROM " + tableName4 + " q WHERE o.\"item_id\" = q.\"item_id\" GROUP BY quantity)
order by \"order_id\"";
 
 Review comment:
   If we don't add the order by , the order of the query result is reverse after this patch,
just as:
               assertTrue (rs.next());
               assertEquals(rs.getString(1), "000000000000004");
               assertEquals(rs.getString(2), "T6");
               assertTrue (rs.next());
               assertEquals(rs.getString(1), "000000000000002");
               assertEquals(rs.getString(2), "T6");
   
   That is because after the `SubqueryRewriter.transform`,the original sql is rewritten as
:
   
   ```
    SELECT ORDER_ID,NAME FROM ORDERTABLE O  
    Inner JOIN ITEMTABLE I  
    ON (O.ITEM_ID = I.ITEM_ID) 
    Inner JOIN (SELECT  COLLECTDISTINCT($3.$4) $5,$3.$6 $2 FROM (SELECT QUANTITY $4,Q.ITEM_ID
$6 FROM ORDERTABLE Q  GROUP BY Q.ITEM_ID,QUANTITY) $3 GROUP BY $3.$6) $1 
    ON (O.ITEM_ID = $1.$2) WHERE  QUANTITY != ANY($1.$5)
   ```
   Without this patch, after the following first `SortMergeJoin` is completed, 
   ```
   SELECT ORDER_ID,NAME FROM ORDERTABLE O  
    Inner JOIN ITEMTABLE I  
    ON (O.ITEM_ID = I.ITEM_ID) 
   ```
   an additional `CLIENT SORTED BY [O.ITEM_ID]`  is added in order to complete the second
`SortMergeJoin`, which unfortunately changes the order of two tuples with the same  `O.ITEM_ID`
which is `0000000006`.
   
   With this patch, the unnecessary `CLIENT SORTED BY [O.ITEM_ID]` is avoid, the order of
tuple is untouched after the first `SortMergeJoin`, so the final SortMergeJoin result is not
same as without this patch.
   
   To make the query result stable regardless of any optimization, order by \"order_id\" is
added.

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