barcode generator vb.net Advanced Stored Procedure Programming in Software

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Advanced Stored Procedure Programming
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SQL Server 2000 Stored Procedure Programming
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his chapter introduces some advanced techniques for coding stored procedures, including Dynamically constructed queries Optimistic locking using timestamps Full-text search and indexes Nested stored procedures Temporary tables Parameterized queries Putting the results of a stored procedure into a table Techniques for generating unique identifiers and potential problems associated with their use The Uniqueidentifier (GUID) datatype Property management using extended properties
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DYNAMICALLY CONSTRUCTED QUERIES
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In this section, we will examine some ways in which you can construct queries dynamically, including
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Executing a string statement Querying by form Using parameterized queries
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Executing a String
Transact-SQL contains a variation of the Execute statement that you can use to run a batch recorded in the form of a character string:
EXEC[UTE] ({@string_variable | [N]'tsql_string'} [+...n])
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Advanced Stored Procedure Programming
Developers can supply a Transact-SQL batch in the form of a character string, a variable, or an expression.
Exec ('select * from Contact')
This statement allows you to assemble a batch or a query dynamically. This might look like magic to you:
declare @chvTable sysname set @chvTable = 'Contact' Exec ('select * from ' + @chvTable)
This syntax is required because the following batch, which you might expect to work, will actually result in a syntax error:
declare @chvTable sysname set @chvTable = 'Contact' select * from @chvTable -- this will cause an error
The error occurs because SQL Server expects a table name rather than a string expression in a From clause. It is important for you to realize that you are dealing with two separate batches in the first example. You cannot use variables from the batch that initiated the Execute statement in the other batch. For example, the following code will result in a syntax error:
declare @chvTable sysname set @chvTable = 'Contact' Exec ('select * from @chvTable')
You cannot use a database context from the other batch either:
Use Asset exec ('Use Northwind select * from Employees') select * from Employees -- Error
SQL Server 2000 Stored Procedure Programming
Query By Form
One of the simplest way to create a search form in a client application is to list all the fields in a table as text boxes on a form. The user will fill some of them in, and they can be interpreted as search criteria:
The trouble with this kind of solution is that most of the time, most of the text-boxes will be left empty. This does not mean that the user wants to find only those records in which the values of these fields are set to empty strings, but that those fields that the user leaves blank should not be included in the criteria. Stored procedures have a static structure, but something dynamic would be more appropriate to launch this kind of query. The following stored procedure assembles a character-string query. The contents of the Where clause are based on the criteria that were specified (that is, fields that were not set to null). When all components are merged, the query returns a list of matching contacts:
Create Procedure prQbfContact_1 -- Dynamically assemble a query based on specified parameters. ( @chvFirstName @chvLastName @chvPhone @chvFax @chvEmail @insOrgUnitId @chvUserName @debug ) varchar(30) varchar(30) typPhone typPhone typEmail smallint varchar(50) int = NULL, = NULL, = NULL, = NULL, = NULL, = NULL, = NULL, = 0
10:
Advanced Stored Procedure Programming
As set nocount on Declare @intErrorCode int, @intTransactionCountOnEntry int, @chvQuery varchar(8000), @chvWhere varchar(8000) Select @intErrorCode = @@Error, @chvQuery = 'SET QUOTED_IDENTIFIER OFF SELECT * FROM Contact', @chvWhere = '' If @intErrorCode = 0 and @chvFirstName is not null Begin Set @chvWhere = @chvWhere + ' FirstName = "' + @chvFirstName + '" AND' Select @intErrorCode = @@Error End If @intErrorCode = 0 and @chvLastName is not null Begin Set @chvWhere = @chvWhere + ' LastName = "' + @chvLastName + '" AND' Select @intErrorCode = @@Error End If @intErrorCode = 0 and @chvPhone is not null Begin set @chvWhere = @chvWhere + ' Phone = "' + @chvPhone + '" AND' Select @intErrorCode = @@Error End If @intErrorCode = 0 and @chvFax is not null Begin set @chvWhere = @chvWhere + ' Fax = "' + @chvFax + '" AND' Select @intErrorCode = @@Error End If @intErrorCode = 0 and @chvEmail is not null Begin set @chvWhere = @chvWhere + ' Email = "' + @chvEmail + '" AND' Select @intErrorCode = @@Error End
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