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Is it a good idea to use COLUMN AS (left([Another_Column],(4)) instead of LEFT in the select?


Which problems arise, declaring the size of all varchar parameters as max in stored proc?How to add/update a column with an incremented value and reset said value based on another column in SQLCan I create a computed column that requires input to select?Can I tell SQL Server not to place data in the buffer cache?Storing NULL versus storing '' in a varchar columnSQL Server - Sudden log autogrowth after database backupProper table design for sparse primary keyReclaim space from dropped column in SQLServer2008R2Int for identity/primary key and Guid for public identifier, best practices?






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;








2















I came across a table like this:



CREATE TABLE TABLE1
(
CD1 int
,CD2 varchar(16)
,CD3 varchar(21)
,CD4 decimal(14,0)
,CD5 varchar(4)
,CD6 decimal(18,2)
,CD7 AS (left([CD3],(4)))
)


This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).



As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.



Isn't it better to select that field during the select when needed?










share|improve this question
































    2















    I came across a table like this:



    CREATE TABLE TABLE1
    (
    CD1 int
    ,CD2 varchar(16)
    ,CD3 varchar(21)
    ,CD4 decimal(14,0)
    ,CD5 varchar(4)
    ,CD6 decimal(18,2)
    ,CD7 AS (left([CD3],(4)))
    )


    This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).



    As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.



    Isn't it better to select that field during the select when needed?










    share|improve this question




























      2












      2








      2








      I came across a table like this:



      CREATE TABLE TABLE1
      (
      CD1 int
      ,CD2 varchar(16)
      ,CD3 varchar(21)
      ,CD4 decimal(14,0)
      ,CD5 varchar(4)
      ,CD6 decimal(18,2)
      ,CD7 AS (left([CD3],(4)))
      )


      This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).



      As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.



      Isn't it better to select that field during the select when needed?










      share|improve this question
















      I came across a table like this:



      CREATE TABLE TABLE1
      (
      CD1 int
      ,CD2 varchar(16)
      ,CD3 varchar(21)
      ,CD4 decimal(14,0)
      ,CD5 varchar(4)
      ,CD6 decimal(18,2)
      ,CD7 AS (left([CD3],(4)))
      )


      This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).



      As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.



      Isn't it better to select that field during the select when needed?







      sql-server sql-server-2008-r2 t-sql






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Mar 28 at 19:41









      Josh Darnell

      13.6k4 gold badges31 silver badges63 bronze badges




      13.6k4 gold badges31 silver badges63 bronze badges










      asked Mar 28 at 12:48









      Racer SQLRacer SQL

      3,5015 gold badges31 silver badges74 bronze badges




      3,5015 gold badges31 silver badges74 bronze badges























          2 Answers
          2






          active

          oldest

          votes


















          8
















          If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".






          share|improve this answer
































            4
















            The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.



            If the computed column is, indeed, indexed, then the it's valuable because:



            • it would required less storage than the full 21 char column

            • it would incur less page reads for seeks and scans than an index on the full 21 char column

            You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.



            If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.






            share|improve this answer



























              Your Answer








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              2 Answers
              2






              active

              oldest

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              2 Answers
              2






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes









              8
















              If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".






              share|improve this answer





























                8
















                If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".






                share|improve this answer



























                  8














                  8










                  8









                  If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".






                  share|improve this answer













                  If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Mar 28 at 12:49









                  Erik DarlingErik Darling

                  27.6k13 gold badges84 silver badges139 bronze badges




                  27.6k13 gold badges84 silver badges139 bronze badges


























                      4
















                      The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.



                      If the computed column is, indeed, indexed, then the it's valuable because:



                      • it would required less storage than the full 21 char column

                      • it would incur less page reads for seeks and scans than an index on the full 21 char column

                      You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.



                      If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.






                      share|improve this answer





























                        4
















                        The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.



                        If the computed column is, indeed, indexed, then the it's valuable because:



                        • it would required less storage than the full 21 char column

                        • it would incur less page reads for seeks and scans than an index on the full 21 char column

                        You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.



                        If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.






                        share|improve this answer



























                          4














                          4










                          4









                          The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.



                          If the computed column is, indeed, indexed, then the it's valuable because:



                          • it would required less storage than the full 21 char column

                          • it would incur less page reads for seeks and scans than an index on the full 21 char column

                          You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.



                          If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.






                          share|improve this answer













                          The only reason I can think of for having that column is to index it, because there is some common set of read queries that filter on the first few characters in CD3.



                          If the computed column is, indeed, indexed, then the it's valuable because:



                          • it would required less storage than the full 21 char column

                          • it would incur less page reads for seeks and scans than an index on the full 21 char column

                          You mentioned the table is rarely read, but I would check for indexes that use this computed column to be sure.



                          If it's not indexed, then see Erik's answer about the storage aspect of non-persisted computed columns.







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered Mar 28 at 19:40









                          Josh DarnellJosh Darnell

                          13.6k4 gold badges31 silver badges63 bronze badges




                          13.6k4 gold badges31 silver badges63 bronze badges































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