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USE tempdb; IF OBJECT_ID('dbo.V1', 'V') IS NOT NULL DROP VIEW dbo.V1; IF OBJECT_ID('dbo.T1', 'U') IS NOT NULL DROP TABLE dbo.T1; GO CREATE TABLE dbo.T1(col1 INT, col2 INT); INSERT INTO dbo.T1(col1, col2) VALUES(1, 2); GO CREATE VIEW dbo.V1 AS SELECT * FROM dbo.T1; GO
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As a practice, avoid using * in your SELECT statements . I m using it here just for demonstration purposes . When V1 was initially created, SQL Server stored metadata information about the columns that existed at that point in time col1 and col2 . Run the following code to query the view:
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SELECT * FROM dbo.V1;
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You get the following output with both columns:
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col1 col2 ----------- ----------1 2
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Next, add a column to T1:
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ALTER TABLE dbo.T1 ADD col3 INT;
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The schema change in T1 was not reflected in the view s metadata information . As far as SQL Server is concerned, the view still has just two columns . If you execute the previous SELECT query again, you still get only two columns in the output:
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col1 col2 ----------- ----------1 2
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To refresh the view s metadata information, run the sp_refreshview stored procedure against V1:
EXEC sp_refreshview 'dbo.V1';
Execute the previous SELECT query again, and you get the following output, which includes the new column col3:
col1 col2 col3 ----------- ----------- ----------1 2 NULL
This is just one example where a schema change in the underlying objects is not reflected in the view s metadata information . You might find it to be a good practice to refresh all views
Inside Microsoft SQL Server 2008: T-SQL Programming
metadata information after applying schema changes to objects in the database . To avoid the tedious process of writing the sp_refreshview statements you can use the following query:
SELECT N'EXEC sp_refreshview ' + QUOTENAME(SCHEMA_NAME(schema_id) + N'.' + QUOTENAME(name), '''') + ';' AS cmd FROM sys.views WHERE OBJECTPROPERTY(object_id, 'IsSchemaBound') = 0;
The query generates as its output the lines of code with the sp_refreshview statements against all views in the database that are not schema-bound . Warning Make sure that you examine the output carefully before running it . Someone with
permission to create views can maliciously plant specially crafted view names to subvert this maintenance code into doing damage .
When you re done, drop V1 and T1:
USE tempdb; IF OBJECT_ID('dbo.V1', 'V') IS NOT NULL DROP VIEW dbo.V1; IF OBJECT_ID('dbo.T1', 'U') IS NOT NULL DROP TABLE dbo.T1;
Modular Approach
You can use views to develop solutions in a modular way . You solve each step of the problem with a query, and define a view based on that query . This process simplifies the solution by allowing you to focus on a single step at a time . I ll demonstrate a modular approach through an example . First, run the following code to create and populate the Sales table in the tempdb database:
SET NOCOUNT ON; USE tempdb; IF OBJECT_ID('dbo.Sales', 'U') IS NOT NULL DROP TABLE dbo.Sales; GO CREATE TABLE dbo.Sales ( mnth DATE NOT NULL PRIMARY KEY, /* Note: The DATE type is new in SQL Server 2008. In earlier versions use DATETIME. */ qty INT NOT NULL ); INSERT INTO dbo.Sales(mnth, qty) VALUES /* Note: Table Value Constructor (enhanced VALUES clause) is new in SQL Server 2008. In earlier versions use a separate INSERT VALUES statement for each row. */
1 Views
('20071201', ('20080101', ('20080201', ('20080301', ('20080401', ('20080501', ('20080601', ('20080701', ('20080801', ('20080901', ('20081001', ('20081101', ('20081201', ('20090101', ('20090201', ('20090301', ('20090401', ('20090501', ('20090601', ('20090701', ('20090801', ('20090901', ('20091001', ('20091101', ('20091201', 100), 110), 120), 130), 140), 140), 130), 120), 110), 100), 110), 100), 120), 130), 140), 100), 100), 100), 110), 120), 110), 120), 130), 140), 100);
Note This code uses features that were introduced in SQL Server 2008 . Those are the DATE
data type and the enhanced VALUES clause that allows inserting multiple rows using a single INSERT VALUES statement . If you re running this code on an earlier version of SQL Server, use the DATETIME data type and a separate INSERT statement for each row .
The table contains one row per month with the sales quantity (column qty) and month (column mnth) . Notice that I used the DATE data type to store a month to support date-related calculations . Even though I care only about the year and month elements of the value, I had to specify something in the day portion . So I specified the first day of each month as the day . When you need to present the data, you can always extract the relevant elements from the full date value . The task at hand is to return groups of consecutive months that have the same sales trend; that is, identify ranges of months with the same trend (up, same, down, or unknown), and indicate the trend with a string column trend . The trend for a given month is based on its qty value minus the qty value of the previous month . If the difference is positive, the trend is up ; if it s negative, the trend is down ; if it s zero, the trend is same ; otherwise, the trend is unknown . The following is the desired result:
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