08 April 2011

Searching a Value within a Database

    Some years back, in a Management meeting related to one of the projects I was working on, one of the Managers made a quite interesting statement, something like: “it should be easy to pool in an Excel sheet from the whole database all the information I am interested in”. I kind of smiled, because the information he was requiring was spanning within different modules, having different levels of detail and thus requiring several different output datasets in order to answer a simple question like “how is the manufacturing cost varying over time?”. After some meetings we figured out that it’s not so easy to pull the data for the respective question, lacking some data which were not available in the respective database. It’s funny how IS (Information Systems) are getting more complex day by day but fail to capture and indirectly answer simple questions, this also because they were not designed to address such questions. Anyway, this post is not about this.

    Some days back I spent a couple of hours trying to identify the tables from which the IDs stored in a log where coming from, in the log being saved no reference to the table, just the IDs. Another example of “good” design! While working diligently, I remembered that I could have easily solved the problem if I were using one of the CLR functions created in a post on Data Profiling Using CLR Functions. Unfortunately, because I was working in a production environment with strong security constraints, I wasn’t allowed registering and use any of the respective functions. Still, considering the easiness and flexibility of a the solution I thought that would be interesting to put it into practice. Who knows, maybe someday I will find the opportunity to use it!

    Let’s suppose I am searching for an integer ID value within a given schema of AdventureWorks database. So, in theory, I need to do a search on each integer column of all the tables from the respective schema. The tables can be found in a matter of seconds using the following query based on the dbo.ExecuteScalarToInt CLR function introduced in the previous mention post and dbo.vTableColumns view.
-- searching a value in whole database

    SELECT [Schema_Name]
    , Table_Name
    , Column_Name
    , system_type
    , dbo.ExecuteScalarToInt('SELECT count(*) FROM ' + Quotename([Schema_Name]) + '.' + Quotename(Table_Name) + ' WHERE ' + Quotename(Column_Name) + ' = ' + Cast(1001 as varchar(20))) NumberRecords
    FROM dbo.vTableColumns
    WHERE [Schema_Name]= 'Sales'

     --AND Table_Name = 'SalesOrderDetail'

     --AND Column_Name = 'SalesOrderDetailID'

     AND system_type = 'int'


BY [Schema_Name]

, Table_Name

, Column_Name
search in database

    As can be seen the dynamically built query, based on table metadata and searched value, is provided as parameter to dbo.ExecuteScalarToInt function. The query calculates the number of occurrences (see NumberRecords column) of the same value within a given column. Some attention must be given to the search column’s data type, as the data type needs to be compatible with the searched value, otherwise a cast being necessary. I haven’t tried the query in a big database and I would advice you to be cautious when running it in a production environment. In case you arrive to use the query in a big database, please let me know how it behaved!

    In case of the problem I had a few days back, the above query it’s only a first step in identifying the tables in which the values occur. Because multiple tables are returned, it’s needed to investigate which of the tables has the highest probability to be the source for the ID saved in log. Of course, some DM (data mining) algorithm could be probably used for this purpose, however some programming is needed and also some amount of diligent work to prove the data. It would be nice to have a tool that performs such analysis or that creates a complex query using any set of attributes within a given database.

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