Database

21-Dec-10 17:08

Hey all,

I am trying to construct a basic search query and am having trouble with my wildcard searches.

I am using C# Visual Studio 2008 and the dataset query designer.

The part of the query I am struggling with is:

WHERE (Land_use_code LIKE '%' +@Landusecode1 + '%')

However, when I run the query, it doesn't perform as I would expect.

There are multiple table entries, with some as follows:
R1
R3
R30

If I enter R and run the query, it returns nothing. If I enter R1, it returns all that match R1.

If I enter R%, it will return R1 and R3, but not R30. If I enter R%%, I will get all records.

I am wondering of a way to enable me to enter R% and get all records returned.

Thanks,

Joe

Luc Pattyn21-Dec-10 17:41

21-Dec-10 17:41

I think there is a problem with the quotes.

with a literal search, it would have to look like this:

WHERE Land_use_code LIKE '%R%'

so the entire literal string (with the percent signs if any) is inside quotes, as it is a string literal, not a numeric literal.

I'm not sure how that works with a variable in SQL.
FWIW: In C# it would be:

new SQLCommand("...WHERE (Land_use_code LIKE '%" + Landusecode1 + "%'");

BTW: you didn't mention what database was used; different databases might use different wildcard characters, and there could even be a character matching any single character, and another matching any sequence of characters.

Smile | :)

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Joe Stansfield21-Dec-10 18:12

21-Dec-10 18:12

Thanks Luc,

I am using SQL Server 2008.

So with your C# example there, you are passing in the variable Landusecode1 to the query and then applying the wildcards aren't you.

If that is how I need to approach it then I can manage to sort it out, I just thought there might be an easier way (as you said - possibly a multiple character wildcard).

Joe

Luc Pattyn21-Dec-10 18:16

21-Dec-10 18:16

Hi Joe,

This page[^] suggests SQL variables can sit inside quotes (I know PHP does that), so it could be as simple as:

WHERE Land_use_code LIKE '%@Landusecode1%'

Beware the (absence of) spaces inside the quoted stuff.

Smile | :)

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Joe Stansfield21-Dec-10 18:23

Re: SQL Wildcard (%) query [modified]

21-Dec-10 18:23

From the look of it, the original

Land_use_code LIKE '%' + @Landusecode1 + '%

is the correct way. I might need to look into using combo boxes with equals|like in it to control the results a bit more, and code the query as necessary from those.

Just a bit more than I wanted to have to do! But no doubt it will be good experience!

Thanks for your help Smile | :)

Luc Pattyn21-Dec-10 18:29

21-Dec-10 18:29

Joe Stansfield wrote:
From the look of it, the original
Land_use_code LIKE '%' + @Landusecode1 + '%
is the correct way.

~~No way, you really need the percent signs and the known content all inside a single pair of quotes.~~

Where is yous snippet sitting, inside a programming language or inside an SQL procedure? maybe show a bit more of it, and somebody will fix it for you.

Smile | :)

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modified on Wednesday, December 22, 2010 7:41 AM

Joe Stansfield21-Dec-10 18:38

21-Dec-10 18:38

It's sitting inside a datasource as a query (so similar to a stored procedure?) and then executed via a button and a table adapter in the programming language.

This is the full query as it sits at the moment:

SELECT File_Name, PID, Address_1, Address_2, Locality, Municipality, Postcode, Sale_date, Sale_price, Total, Capital_value, Land_area, Land_use_code, Room_count, Building_area, Construction_year, Wall_construction_code, Roof_construction_code, Land, Rate_1, Val_Ref, Source FROM vSaleSearch 
WHERE (Municipality = @Municiaplity1 OR Municipality = @Municipality2)
AND (Locality LIKE @Locality + '%' OR Locality = @Locality1 OR Locality = @Locality2) 
AND (Land_use_code LIKE '%' + @Landusecode1 + '%')
AND (Sale_price >= @Sale_Price1 )
AND ( Sale_price <= @Sale_Price2) 
AND (Sale_date >= @Sale_Date1) 
ORDER BY Sale_price

I'm trying to achieve the same thing on the locality. What I'd ideally like is for a person to be able to enter a string in the locality field and it take it as an "equals" query. Or include a wild card at the start or end to take it as a like and apply the wild card characters.

At the moment it achieves half of that, but not as user friendly as one might hope... I see what I want to happen all the time, but of course I'm not sure how exactly it is done...

Luc Pattyn22-Dec-10 1:30

22-Dec-10 1:30

When the query is a string built in a programming language (say C#), then this[^] seems to show the way. Basically, apply the wildcard characters (if you want them, this might depend on a CheckBox being checked) to the parameter before you set up the SQLParameter, then write your query without any quotes.

Smile | :)

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PIEBALDconsult22-Dec-10 3:38

PIEBALDconsult

22-Dec-10 3:38

Add the percent signs to the parameter value.

parm.Value = "%" + foo + "%"

jschell23-Dec-10 8:04

jschell

23-Dec-10 8:04

Joe Stansfield wrote:
If I enter R%%, I will get all records.

And if you enter R%%% do you get no records?

Via SQL Server 2005 directly I am unable to replicate what you are seeing.

Joe Stansfield wrote:
I am using C# Visual Studio 2008 and the dataset query designer.

It is possible that the latter is the problem.

In Server 2005 (not the designer) I get exactly or at least close to the behaviour you describe when I use the underscore rather than the percent sign. Especially when you try the different input values.

Even if the SQL created excluded the percent signs from your where clause when you entered them manually it should still work. Instead with a single one you get only a single match. With two you get a two character match. That suggests the underline (single character match.)

Presuming there isn't some other assumption that is wrong - such as that you are actually running some other query because this one didn't get applied.

Simple test. Remove the percent entirely from the expression. Then test with input values: R, R_ and R%.
Those should give different results. If not then I would suspect that there is some other assumption that is causing the problem.

Joe Stansfield5-Jan-11 11:53

Extracting a blob data file from sqlite

5-Jan-11 11:53

Sorry about the delayed reply - christmas / new year break over here in sunny Australia!

I tried all of the things above, and get identical results when using R% as I do R_. I have found that when using R%% I do get all records, but I have since discovered this is only because the maximum length of a record is 3 characters. I get the same result if I use R%%%.

However, when I use the wildcard part of the query on the Locality choice, it works as I would expect it too, and returns all results that start with, say, 'Hob', if I enter Hob%.

The only difference I can think of between the two is that Locality is stored as 'NVARCHAR(50)' and Land_Use_Code as 'NCHAR(5)'. I would not have thought this would cause a problem, but I may be wrong!

In the mean time I will work around it and add multiple %% signs to the parameter before the query is executed. Unfortunately I have tried to get my head around writing parametrized queries from scratch, but have not been able to find a good resource that explains it along with using it to then fill a DataGridView.

Thanks for all your help though guys - has been great and I feel like I have learnt a lot!

crain198121-Dec-10 13:35

21-Dec-10 13:35

If (Decrypt_TextBox.Text = "") Then
               MessageBox.Show("Need to put in the file location or select file in grid for decryption")
           Else

               'declaring string for file'
               Dim filename As String
               'Getting the file name that is selected'

               filename = getFilename()
               'Starting to abstract the data from the database'
               database.ConnectionString = "Data Source = test.db3;"
               database.Open()
               Dim command As SQLite.SQLiteCommand
               Dim sqlstatement As String
               command = database.CreateCommand
               'The following will get the bytes of the file'
               Dim filesize As Integer
               sqlstatement = "SELECT FileSize From Vault WHERE FileName=@file;"
               command.CommandText = sqlstatement
               command.Parameters.AddWithValue("@file", filename)
               Dim reader As SQLite.SQLiteDataReader
               reader = command.ExecuteReader
               filesize = reader.GetValue(0)
               reader.Close()
               Dim data(filesize) As Byte
               'The following should get the data'
               sqlstatement = "SELECT FileData FROM Vault WHERE FileName=@file;"
               command.CommandText = sqlstatement
               command.Parameters.AddWithValue("@file", filename)
               reader = command.ExecuteReader

I have encrypted files in this database. I need to extract this file and decrypt it. I've been thinking about using a memory stream but these files will get fairly large (2GB). This is as far as I've gotten using vb .net framework 2.0. Any help is helpful?

Luc Pattyn21-Dec-10 13:55

21-Dec-10 13:55

where do the files originate, how did they get encrypted, how did they enter the database?
would retrieving them not be pretty much the reverse process?

and why is it you store them in the database to begin with? I wouldn't store gigablobs, I'd use files and store the file's path in the db.

Smile | :)

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crain198121-Dec-10 14:34

21-Dec-10 14:34

At first its encrypted using SHA1 as a file and stored into the database. The problem is that sqlite libraries doesn't give me a clear picture on how to extract the file. After further research and bouncing ideas of people, they have suggested binarystream and it goes make since but i don't know how it will the end will be just yet.

Luc Pattyn21-Dec-10 14:41

21-Dec-10 14:41

I expect one uses a byte array to write or read a blob field; and a stream to encrypt or decrypt; so basically reading from the database and decrypting should be pretty much the same as encrypting and writing to the database. If the latter works for huge files, so should the former.

Suggestion: try and solve the problem without any encryption/decryption first; then add them in.

Smile | :)

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crain198121-Dec-10 15:04

21-Dec-10 15:04

Still don't how to extract the file either way.

Luc 64801121-Dec-10 16:19

Luc 648011

21-Dec-10 16:19

I have no experience with SQLite.

However I did search CodeProject articles for SQL read BLOB and found a lot, including this: Reading and Writing BLOB Data to Microsoft SQL or Oracle Database[^]. I'm sorry the examples are in C#, that does not change the philosophy, it merely changes the syntax of things.

I suggest you read it, or some of the other hits, and try what you learn. I once more stress the fact that IMO writing to a BLOB field and reading from a BLOB field are bound to be very similar.

Smile | :)

crain19818-Jan-11 5:27