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Posted Tuesday, January 10, 2012 8:05 AM
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Hi All,
I have a very interesting situation. I am pulling following string (see Coulmn1) using substring,replace..etc. from the varchar(5000). I want to execute it as a mathematical expression and want the result shown in Column2.

Column1 --------------- Coulmn2
2 * 2+1 * 7 --------------- 11
1 * 1+2 * 4 --------------- 9
1 * 1+2 * 4+1 * 4 --------- 13
Post #1233252
Posted Tuesday, January 10, 2012 8:12 AM


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What about operator precedence? If it needs to be calculated from left to right, it would be easy with string operations. Operator precedence will make it little complicated.

Please provide us DDL, sample data to play with.


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Post #1233262
Posted Tuesday, January 10, 2012 8:17 AM


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BEGIN TRAN

CREATE TABLE yourTable (yourTableID INT IDENTITY, column1 VARCHAR(500), column2 VARCHAR(500))
INSERT INTO yourTable (column1)
SELECT '2 * 2+1 * 7'
UNION ALL SELECT '1 * 1+2 * 4'
UNION ALL SELECT '1 * 1+2 * 4+1 * 4'

DECLARE @SQL AS VARCHAR(MAX)

SELECT @SQL = COALESCE(@SQL + ';' + CHAR(10),'') +
'UPDATE yourTable SET column2= ' + column1 + ' WHERE yourTableID = '+CAST(yourTableID AS VARCHAR(3))
FROM yourTable

PRINT @SQL

EXEC(@SQL)

--Check results
SELECT * FROM yourTable

ROLLBACK




Not a DBA, just trying to learn

For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/

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If you litter your database queries with nolock query hints, are you aware of the side effects?
Try reading a few of these links...

(*) Missing rows with nolock
(*) Allocation order scans with nolock
(*) Consistency issues with nolock
(*) Transient Corruption Errors in SQL Server error log caused by nolock
(*) Dirty reads, read errors, reading rows twice and missing rows with nolock


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Post #1233267
Posted Tuesday, January 10, 2012 8:24 AM


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Nice!


Help us to help you. For better, quicker and more-focused answers to your questions, consider following the advice in this link.

When you ask a question (and please do ask a question: "My T-SQL does not work" just doesn't cut it), please provide enough information for us to understand its context.
Post #1233275
Posted Tuesday, January 10, 2012 11:31 AM
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This is working but I am looking soothing like a scaler function that can be used in Select statement. Any idea?

select ..., dbo.fnExpressionToValue(Expr)
from myTable
Post #1233431
Posted Wednesday, January 11, 2012 2:19 AM


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kausmail (1/10/2012)
This is working but I am looking soothing like a scaler function that can be used in Select statement. Any idea?

select ..., dbo.fnExpressionToValue(Expr)
from myTable


That's a different requirement to the one you originally stated.

In this case, you'd have to use a CLR as you can't execute a string in a function. If you need help writing one (and someone else doesn't post one in between), I'll knock up a simple one later on today.



Not a DBA, just trying to learn

For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better, quicker answers on SQL Server performance related questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/



If you litter your database queries with nolock query hints, are you aware of the side effects?
Try reading a few of these links...

(*) Missing rows with nolock
(*) Allocation order scans with nolock
(*) Consistency issues with nolock
(*) Transient Corruption Errors in SQL Server error log caused by nolock
(*) Dirty reads, read errors, reading rows twice and missing rows with nolock


LinkedIn | Blog coming soon (for sufficiently large values of "soon" )!
Post #1233800
Posted Thursday, January 12, 2012 3:03 AM


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Cadavre (1/11/2012)
In this case, you'd have to use a CLR as you can't execute a string in a function. If you need help writing one (and someone else doesn't post one in between), I'll knock up a simple one later on today.


Well, running a little late obviously

Nice and simple CLR, I've not exactly thoroughly tested this so you'll want to do lots of tests first.

using System;
using System.Data;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;

namespace executeString
{
public class UserDefinedFunctions
{
[SqlFunction]
public static SqlString ExecuteString(SqlString maths)
{
var mathString = maths.ToString().Replace(" ", "");
string mathResult;
try
{
var result = new DataTable().Compute(mathString, null);
mathResult = result.ToString();
}
catch (Exception)
{
mathResult = null;
}

mathResult = string.IsNullOrEmpty(mathResult) ? null : mathResult;

return new SqlString(mathResult);
}
};
}

BEGIN TRAN

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[ExecuteString]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
DROP FUNCTION [dbo].[ExecuteString]
IF EXISTS (SELECT * FROM sys.assemblies asms WHERE asms.name = N'executeString' and is_user_defined = 1)
DROP ASSEMBLY [executeString]
GO
CREATE ASSEMBLY [executeString]
AUTHORIZATION [dbo]
FROM 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WITH PERMISSION_SET = SAFE
GO
CREATE FUNCTION [dbo].[ExecuteString](@maths [nvarchar](4000))
RETURNS [nvarchar](4000) WITH EXECUTE AS CALLER
AS
EXTERNAL NAME [executeString].[executeString.UserDefinedFunctions].[ExecuteString]
GO

CREATE TABLE yourTable (yourTableID INT IDENTITY, column1 VARCHAR(500), column2 VARCHAR(500))
INSERT INTO yourTable (column1)
SELECT '2 * 2+1 * 7'
UNION ALL SELECT '1 * 1+2 * 4'
UNION ALL SELECT '1 * 1+2 * 4+1 * 4'

SELECT column1, [dbo].[ExecuteString] (column1)
FROM yourTable

ROLLBACK

Which will return: -
column1                                                                                                                                                                                                                                                          
------------------- --------------------
2 * 2+1 * 7 11
1 * 1+2 * 4 9
1 * 1+2 * 4+1 * 4 13


Since you never replied to my last message, I'm assuming that a CLR is an option for you?



Not a DBA, just trying to learn

For better, quicker answers on T-SQL questions, click on the following...
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better, quicker answers on SQL Server performance related questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/



If you litter your database queries with nolock query hints, are you aware of the side effects?
Try reading a few of these links...

(*) Missing rows with nolock
(*) Allocation order scans with nolock
(*) Consistency issues with nolock
(*) Transient Corruption Errors in SQL Server error log caused by nolock
(*) Dirty reads, read errors, reading rows twice and missing rows with nolock


LinkedIn | Blog coming soon (for sufficiently large values of "soon" )!
Post #1234601
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