Question

I am trying to implement an idea where I have two sql tables in a database.

Table Info which has a field Nationality and the other Table Exclusion which has a field Keyword.

`Info.Nationality`               `Exclusion.Keyword`

    |British|                     |France|  
    |resteraunt de France|        |Spanish|
    |German|
    |Flag Italian|
    |Spanish rice|
    |Italian pasta
    |Irish beef|

In my web application I am creating a GridView4 and through a DataTable and SqlDataAdapter I am populating that GridView4 with the SQL command:

SELECT DISTINCT Info.Nationality WHERE Exclusion.Keyword NOT LIKE '%Spanish%'

That SQL statement retrieves all the distinct records in Info.Nationality which do not contain the word spanish.

What I am currently doing is that in the web app which is in vb.net I am adding two different GridViews, each have the data of each table which means that GridView2 has DISTINCT Info.Nationality and GridView3 has Exclusion.Keyword and then adding another GridView4 to display the results of the above SQL command.

The idea is to retrieve all the distinct records from Info.Nationlity which are not suppressed by the keyword constraints in Exclusion.keyword. So from the above mentioned Sql command the GridView4 will retrieve all the records which do not have the word “Spanish”.

I am doing all of this in a nested for loop where in the first loop it takes each record (one by one) from Info.Nationality e.g.for each row As DataRow in Me.GridView2.Rows() and compare it with the second for loop which goes till the end of the Exclusion.Keyword which would be like For i=0 To Gridview3 - 1.

The problem is that in that sql statement I have to explicitly specify the word to compare. I tried adding the records of Exclusion.Keyword in a String and then replacing the Spanish Keyword In between the NOT LIKE with the name of the String which is Keywords and then assigning the name a parameter with cmd.parameter.addwithvalue(@String, Keywords). However this is not working, it is only comparing with the last record in the string and ignoring the first.

The idea behind all of this is to display all the records of Info.Nationality in GridView4 which do not contain the keywords in Exclusion.Keyword.

Is there an easier or more effecient way to do this? I was thinking of an Inner Join with a Like command but that is not my problem. My problem is that how can I compare each record one by one of Info.Nationlity with all the records in Exclusion.keyword and then retrieving the ones that do not match and discarding the ones that match.

Then in Gridview4 how can I edit the records without reflecting those changes or affecting in Info.Nationality but rather only Inserting to Exclusion.Keyword the changes.

SOLVED by adding ToString() after Text
In my asp.net web app, I tried this, but didn’t work: (SOLVED)

 `SELECT DISTINCT Nationality 
FROM Info Where NOT EXISTS(SELECT * FROM Exclusion WHERE Info.Nationality LIKE '%' + @GridView +'%')`

`cmd.parameters.AddwithValue("@GridView", GridView3.Rows(i).Cells(0).Text.ToString())`

GridView3 Here has the Exclusion.Keywords data.

Would really appreciate your suggestions and thoughts around this.

Answer 1

You do not need to do this one-by-one, or “Row by agonizing row” as some DBAs are fond of describing this type of approach. There are lots of ways to write a query to only return the records from Info.nationality that do not match the exclusion keywords as a single expression.

My preference is to use the EXISTS clause and a correlated subquery:

SELECT Nationality 
FROM Info I
WHERE NOT EXISTS(SELECT * FROM Exclusion WHERE I.Nationality LIKE '%' + Keyword + '%')

You can also express this as a left join.

SELECT I.Nationality 
FROM Info I
    LEFT OUTER JOIN Exclusion E 
        ON I.Nationality LIKE '%' + E.Keyword + '%'
WHERE E.Keyword IS NULL 

The left join will return all the rows from info and insert nulls in the columns for Exclusion except where the join criteria matches. By filtering for only where those values are null, you can avoid the matches.