the datatype

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  • John Kevien
    #1

    the datatype


    hello !

    I got some problems here. I have an attribute that determines the unit
    of something,e.g. the size of using "mm" , the length of using "seconds"
    and something others may using "n-page", so ,which data type should I
    use. the "nvarchar" or others?


    thank you very much!



    *** Sent via Developersdex http://www.developersdex.com ***
    Tags: None
    • --CELKO--
      #2
      Re: the datatype

      >> I have an attribute that determines the unit of something,e.g. the size of using "mm" , the length of using "seconds" and something others may using "n-page", so ,which data type should I use. the "nvarchar" or others? <<

      You need to learn how a relational design works. What meaningful name
      could you give such a column? "some_kind_of_u nit" or "don't_know_uni t"
      or "could_be_anyth ing" is a bit vague. Since seconds cannot be
      transformed into volts, etc. this column is in violation of !NF -- it
      holds several totally different things, like field in a file system.

      Units of measure are part of an attribute's value, not an attribute.
      You are confusing data and meta-data. Get of a copy of SQL PROGRAMMING
      STYLE or SQL FOR SMARTIES and read the chapters on scales and
      measurements, and the design of encoding schemes.

        Comment

        • Tony Rogerson
          #3
          Re: the datatype

          If you are just storing the description, eg...

          mm
          seconds
          n-page

          then I'd hold them using nvarchar and size it according to the maxium length
          you expect, if its just the above then nvarchar(7).

          If you are talking about the units themselves then i'd go down this
          route....

          create table unit_type (
          id int not null identity constraint sk_unit_type unique clustered,
          name nvarchar(7) not null constraint pk_unit_type primary key
          nonclustered
          )

          create table measurement (
          unit_type_id int not null references unit_type( id ),
          unit decimal( 10, 5 ) not null
          )

          Hope that helps.

          Tony.

          --
          Tony Rogerson
          SQL Server MVP
          http://sqlblogcasts.com/blogs/tonyrogerson - technical commentary from a SQL
          Server Consultant
          http://sqlserverfaq.com - free video tutorials


          "John Kevien" <kevien-2002@163.com> wrote in message
          news:mJBag.1$RV 2.122@news.uswe st.net...[color=blue]
          >
          > hello !
          >
          > I got some problems here. I have an attribute that determines the unit
          > of something,e.g. the size of using "mm" , the length of using "seconds"
          > and something others may using "n-page", so ,which data type should I
          > use. the "nvarchar" or others?
          >
          >
          > thank you very much!
          >
          >
          >
          > *** Sent via Developersdex http://www.developersdex.com ***[/color]


            Comment

            • Neil
              #4
              Re: the datatype

              Just curious: why nvarchar instead of varchar?

              "Tony Rogerson" <tonyrogerson@s qlserverfaq.com > wrote in message
              news:e4fa0l$327 $1$8300dec7@new s.demon.co.uk.. .[color=blue]
              > If you are just storing the description, eg...
              >
              > mm
              > seconds
              > n-page
              >
              > then I'd hold them using nvarchar and size it according to the maxium
              > length you expect, if its just the above then nvarchar(7).
              >
              > If you are talking about the units themselves then i'd go down this
              > route....
              >
              > create table unit_type (
              > id int not null identity constraint sk_unit_type unique
              > clustered,
              > name nvarchar(7) not null constraint pk_unit_type primary key
              > nonclustered
              > )
              >
              > create table measurement (
              > unit_type_id int not null references unit_type( id ),
              > unit decimal( 10, 5 ) not null
              > )
              >
              > Hope that helps.
              >
              > Tony.
              >
              > --
              > Tony Rogerson
              > SQL Server MVP
              > http://sqlblogcasts.com/blogs/tonyrogerson - technical commentary from a
              > SQL Server Consultant
              > http://sqlserverfaq.com - free video tutorials
              >
              >
              > "John Kevien" <kevien-2002@163.com> wrote in message
              > news:mJBag.1$RV 2.122@news.uswe st.net...[color=green]
              >>
              >> hello !
              >>
              >> I got some problems here. I have an attribute that determines the unit
              >> of something,e.g. the size of using "mm" , the length of using "seconds"
              >> and something others may using "n-page", so ,which data type should I
              >> use. the "nvarchar" or others?
              >>
              >>
              >> thank you very much!
              >>
              >>
              >>
              >> *** Sent via Developersdex http://www.developersdex.com ***[/color]
              >
              >[/color]


                Comment

                • Tony Rogerson
                  #5
                  Re: the datatype

                  Hi Neil,

                  Its the Microsoft recommendation for string data types, use the N (unicode)
                  versions, there are a few things that require unicode if you use SSIS too.

                  I'm finding it a hard habbit to get into!

                  Tony.

                  --
                  Tony Rogerson
                  SQL Server MVP
                  http://sqlblogcasts.com/blogs/tonyrogerson - technical commentary from a SQL
                  Server Consultant
                  http://sqlserverfaq.com - free video tutorials


                  "Neil" <nospam@nospam. net> wrote in message
                  news:wpIag.3219 $x4.3114@newsre ad3.news.pas.ea rthlink.net...[color=blue]
                  > Just curious: why nvarchar instead of varchar?
                  >
                  > "Tony Rogerson" <tonyrogerson@s qlserverfaq.com > wrote in message
                  > news:e4fa0l$327 $1$8300dec7@new s.demon.co.uk.. .[color=green]
                  >> If you are just storing the description, eg...
                  >>
                  >> mm
                  >> seconds
                  >> n-page
                  >>
                  >> then I'd hold them using nvarchar and size it according to the maxium
                  >> length you expect, if its just the above then nvarchar(7).
                  >>
                  >> If you are talking about the units themselves then i'd go down this
                  >> route....
                  >>
                  >> create table unit_type (
                  >> id int not null identity constraint sk_unit_type unique
                  >> clustered,
                  >> name nvarchar(7) not null constraint pk_unit_type primary key
                  >> nonclustered
                  >> )
                  >>
                  >> create table measurement (
                  >> unit_type_id int not null references unit_type( id ),
                  >> unit decimal( 10, 5 ) not null
                  >> )
                  >>
                  >> Hope that helps.
                  >>
                  >> Tony.
                  >>
                  >> --
                  >> Tony Rogerson
                  >> SQL Server MVP
                  >> http://sqlblogcasts.com/blogs/tonyrogerson - technical commentary from a
                  >> SQL Server Consultant
                  >> http://sqlserverfaq.com - free video tutorials
                  >>
                  >>
                  >> "John Kevien" <kevien-2002@163.com> wrote in message
                  >> news:mJBag.1$RV 2.122@news.uswe st.net...[color=darkred]
                  >>>
                  >>> hello !
                  >>>
                  >>> I got some problems here. I have an attribute that determines the unit
                  >>> of something,e.g. the size of using "mm" , the length of using "seconds"
                  >>> and something others may using "n-page", so ,which data type should I
                  >>> use. the "nvarchar" or others?
                  >>>
                  >>>
                  >>> thank you very much!
                  >>>
                  >>>
                  >>>
                  >>> *** Sent via Developersdex http://www.developersdex.com ***[/color]
                  >>
                  >>[/color]
                  >
                  >[/color]


                    Comment

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