in reply to Storing multiple value field in a MySQL database

Wrong solution; If you have a field that needs to hold more than one value, that field usually deserves a new table:

Table1:
userid       email              age
john         john@example.com   45
jerry        jerry@example.com  22


Table2:
userid       memberof
john         admins
john         wizzards
jerry        newbies
jerry        trainees
jerry        newhires

[download]

Dave

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Re^2: Storing multiple value field in a MySQL database
by mba777 (Novice) on Nov 25, 2013 at 19:28 UTC

    Hi Dave, that's clear but i really want all values of the multi value field in one mysql column, is this not possible?

    Thanks Andy

[reply]

      Why?

      davido has illustrated the general layout of the tables for the normal solution. An alternative would be:

      Table1:
userid       email              age memberof
john         john@example.com   45   admins  
john         john@example.com   45   wizzards
jerry        jerry@example.com  22   newbies 
jerry        jerry@example.com  22   trainees
jerry        jerry@example.com  22   newhires

      [download]

      which is obviously dumb because of all the repeated information and the slightly more subtle problem that if jerry's age changes (age does tend to change) you have to fix every 'jerry' row. Or maybe you mean something like:

      Table1:
userid       email              age memberof
john         john@example.com   45   admins!wizzards
jerry        jerry@example.com  22   newbies!trainees!newhires

      [download]

      but then there is no efficient way to search for all newhires.

      So, again, why? What is it about davido's solution that you don't like or can't understand?

      True laziness is hard work
[reply]
[d/l]
[select]

        Hi, i understand davido's solution, and i know that it is the better solution, but i exactly mean something like that:

        Table1:
userid       email              age memberof
john         john@example.com   45   admins,wizzards
jerry        jerry@example.com  22   newbies,trainees,newhires

        [download]

        And i do not need an efficient way to search for all newhires. The filed memberof should only be additional information.

        So can you only show me perhaps an code example how to store multiple value files in one single mysql column. Thanks ;)

[reply]
[d/l]

      Of course you can create one VARCHAR(512), or whatever field, cram a bunch of comma-separated-values into it, and parse them out later. You can do that. But that's not an effective use of your database. It prevents you from easily searching in-database for all users who are a member of "wizzards". Instead you will have to use "LIKE" clauses, which are less efficient, or slurp all records into your script and do your own processing.

      SQL-style databases usually just use another table whenever a developer is tempted to cram more than one item into a given field. There's good reason for that.


      Dave

[reply]

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