Sql-server – Make sure two columns are sorted in the same order

sql servert-sql

I have a table like this:

CREATE TABLE T (
 ID INT NOT NULL IDENTITY PRIMARY KEY,
 CreateDateTime datetime2 NOT NULL,
 --other columns
)

How can I make sure that ID and CreateDateTime are both sorted in the same order? In other words, the following queries would return an identical order:

select * from T order by ID
select * from T order by CreateDateTime

I need this guarantee because for performance reasons I want to query a date range by filtering on the ID column. This is possible if the guarantee holds.

I want to fail DML that would violate that property. My intention is to catch bugs breaking this invariant.

Is there a way to do this without using triggers? My hope is that there is a more elegant solution.

Best Answer

I don't think it's easy to make such a guarantee and even if you do manage to make such an assertion actually work, it may slow down your Inserts into the table.

Since this is a performance issue for the ordering queries, here's a suggestion:

Make (CreateDateTime, ID) or (CreateDateTime) the clustered index of the table, instead of the (usual) clustered index on (ID) alone.

Then you can run queries with ORDER BY CreateDateTime and they will use the clustered index.

Related Solutions

SQL Server Row Differences – How to Show Rows Different Between Two Tables or Queries

You don't need 30 join conditions for a FULL OUTER JOIN here.

You can just Full Outer Join on the PK, preserve rows with at least one difference with WHERE EXISTS (SELECT A.* EXCEPT SELECT B.*) and use CROSS APPLY (SELECT A.* UNION ALL SELECT B.*) to unpivot out both sides of the JOINed rows into individual rows.

WITH TableA(Col1, Col2, Col3) 
     AS (SELECT 'Dog',1,1     UNION ALL 
         SELECT 'Cat',27,86   UNION ALL 
         SELECT 'Cat',128,92), 
     TableB(Col1, Col2, Col3) 
     AS (SELECT 'Dog',1,1     UNION ALL 
         SELECT 'Cat',27,105  UNION ALL 
         SELECT 'Lizard',83,NULL) 
SELECT CA.*
FROM   TableA A 
       FULL OUTER JOIN TableB B 
         ON A.Col1 = B.Col1 
            AND A.Col2 = B.Col2 
/*Unpivot the joined rows*/
CROSS APPLY (SELECT 'TableA' AS what, A.* UNION ALL
             SELECT 'TableB' AS what, B.*) AS CA     
/*Exclude identical rows*/
WHERE  EXISTS (SELECT A.* 
               EXCEPT 
               SELECT B.*) 
/*Discard NULL extended row*/
AND CA.Col1 IS NOT NULL      
ORDER BY CA.Col1, CA.Col2

Gives

what   Col1   Col2        Col3
------ ------ ----------- -----------
TableA Cat    27          86
TableB Cat    27          105
TableA Cat    128         92
TableB Lizard 83          NULL

Or a version dealing with the moved goalposts.

SELECT DISTINCT CA.*
FROM   TableA A 
       FULL OUTER JOIN TableB B 
         ON EXISTS (SELECT A.*  INTERSECT  SELECT B.*) 
CROSS APPLY (SELECT 'TableA' AS what, A.* UNION ALL
             SELECT 'TableB' AS what, B.*) AS CA     
WHERE NOT EXISTS (SELECT A.*  INTERSECT  SELECT B.*) 
AND CA.Col1 IS NOT NULL
ORDER BY CA.Col1, CA.Col2

For tables with many columns it can still be difficult to identify the specific column(s) that differ. For that you can potentially use the below.

(though just on relatively small tables as otherwise this method likely won't have adequate performance)

SELECT t1.primary_key,
       y1.c,
       y1.v,
       y2.v
FROM   t1
       JOIN t2
         ON t1.primary_key = t2.primary_key
       CROSS APPLY (SELECT t1.*
                    FOR xml path('row'), elements xsinil, type) x1(x)
       CROSS APPLY (SELECT t2.*
                    FOR xml path('row'), elements xsinil, type) x2(x)
       CROSS APPLY (SELECT n.n.value('local-name(.)', 'sysname'),
                           n.n.value('.', 'nvarchar(max)')
                    FROM   x1.x.nodes('row/*') AS n(n)) y1(c, v)
       CROSS APPLY (SELECT n.n.value('local-name(.)', 'sysname'),
                           n.n.value('.', 'nvarchar(max)')
                    FROM   x2.x.nodes('row/*') AS n(n)) y2(c, v)
WHERE  y1.c = y2.c
       AND EXISTS(SELECT y1.v
                  EXCEPT
                  SELECT y2.v)

Sql-server – Combine Table Hints INDEX and FORCESEEK with Two Joins Not On PK

I would also test this rewriting (aasuming that sID is the primary key of docSVsys):

SELECT COUNT(*)              
FROM [docSVsys] AS d
WHERE EXISTS
      ( SELECT * 
        FROM [docSVtext] AS sv
        WHERE sv.[sID] = d.[sID] 
          AND sv.[value] = 'doug'
      )
   OR EXISTS
      ( SELECT * 
        FROM [docMVtext] AS mv
        WHERE mv.[sID] = d.[sID] 
          AND mv.[value] = 'doug'
      ) ;

Best Answer

Related Solutions

SQL Server Row Differences – How to Show Rows Different Between Two Tables or Queries

Sql-server – Combine Table Hints INDEX and FORCESEEK with Two Joins Not On PK

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