c# qr code generator Inside Microsoft SQL Server 2008: T-SQL Querying in C#

Drawing QR Code ISO/IEC18004 in C# Inside Microsoft SQL Server 2008: T-SQL Querying

Inside Microsoft SQL Server 2008: T-SQL Querying
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CREATE UNIQUE CLUSTERED INDEX idx_depth_first ON dbo.Employees(hid); CREATE UNIQUE INDEX idx_breadth_first ON dbo.Employees(lvl, hid); CREATE UNIQUE INDEX idx_empid ON dbo.Employees(empid);
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In addition to the hid column that holds the path, the table has a computed persisted column based on the GetLevel method applied to the hid column. As its name implies, the method returns the level of the node in the tree in other words, the distance from the root. Besides the obvious index on the empid attribute that supports queries requesting a particular employee, the code creates two other indexes. First, a clustered index is created on the hid column. Because HIERARCHYID provides topological sorting, an index on the hid column stores all members of the same subtree close to each other. Such an index allows ef cient processing of requests that need to traverse the tree in a depth- rst manner for example, a request for a whole subtree of employees. Second, an index is created on lvl and hid, in that order. This index supports ef cient processing of requests that need to traverse the tree in a breadth- rst manner for example, returning a whole level of employees. Notice that the Employees table does not include an attribute for the manager ID. With the HIERARCHYID type you can easily address requests that would normally require such an attribute.
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Whenever you need to apply changes to the tree, such as adding new leaf nodes or moving a subtree, you want to make sure that you produce new HIERARCHYID values or adjust existing ones correctly. The HIERARCHYID type s methods and properties can help you in such tasks. Also, it s important to note that the type itself does not enforce the validity of your tree that s your responsibility. For example, if you do not enforce uniqueness of the HIERARCHYID values with a constraint, the type itself won t reject attempts to insert multiple rows with the same HIERARCHYID value. Also, it is your responsibility to develop a process that prevents concurrent sessions that perform tree maintenance tasks from producing con icting (the same) HIERARCHYID values for different nodes. I will explain how this can be achieved. I will demonstrate techniques for adding employees who manage no one (leaf nodes) and for moving a subtree. I ll leave other tasks such as dropping a subtree and changing a manager as exercises because those apply similar techniques to the ones I will cover.
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The task of adding a new employee who manages no one requires you to produce a HIERARCHYID value for the new node that positions it correctly within the tree and then
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insert the new employee row into the table. Run the following code to create a stored procedure called AddEmp that implements this task:
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---------------------------------------------------------------------- Stored Procedure: AddEmp, -Inserts new employee who manages no one into the table --------------------------------------------------------------------IF OBJECT_ID('dbo.AddEmp', 'P') IS NOT NULL DROP PROC dbo.AddEmp; GO CREATE PROC dbo.AddEmp @empid AS INT, @mgrid AS INT, @empname AS VARCHAR(25), @salary AS MONEY AS DECLARE @hid AS HIERARCHYID, @mgr_hid AS HIERARCHYID, @last_child_hid AS HIERARCHYID; BEGIN TRAN IF @mgrid IS NULL SET @hid = hierarchyid::GetRoot(); ELSE BEGIN SET @mgr_hid = (SELECT hid FROM dbo.Employees WITH (UPDLOCK) WHERE empid = @mgrid); SET @last_child_hid = (SELECT MAX(hid) FROM dbo.Employees WHERE hid.GetAncestor(1) = @mgr_hid); SET @hid = @mgr_hid.GetDescendant(@last_child_hid, NULL); END INSERT INTO dbo.Employees(empid, hid, empname, salary) VALUES(@empid, @hid, @empname, @salary); COMMIT TRAN GO
The procedure accepts as inputs all attributes of the new employee (employee ID, manager ID, employee name, and salary). It then applies logic to generate the HIERARCHYID value of the new employee and store it in the variable @hid. Finally, the procedure uses the new HIERARCHYID value, @hid, in the new row it inserts into the Employees table. The procedure s code rst checks whether the input employee is the root employee (manager ID is NULL). In such a case, the code calculates the employee s path with the static method hierarchyid::GetRoot. As you can imagine, the purpose of this method is to produce the path for the tree s root node. In terms of the binary value that actually represents the path, this method simply returns an empty binary string (0x). You could, if you wanted, replace the static method call with the constant 0x, but with the method call the code is clearer and more self-explanatory.
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