c# print barcode zebra Inside Microsoft SQL Server 2008: T-SQL Querying in C#.NET

Make QR in C#.NET Inside Microsoft SQL Server 2008: T-SQL Querying

Inside Microsoft SQL Server 2008: T-SQL Querying
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You get the same 23 customers back as those returned by the query applying the positive approach. Notice, though, that the negative solution gives you access to all the customer attributes, while the positive solution gives you access only to the customer IDs. To access other customer attributes, you need to add a join between the result set and the Customers table. When comparing the performance of the solutions in this case, the solution applying the positive approach performs better. In other cases, the negative approach might yield better performance. You now have another tool that you can use when solving problems. Another example where you can apply this kind of reverse logic is in a CHECK constraint that needs to ensure that a character string column (call it sn for serial number) allows only digits. Using positive logic, the constraint s predicate can ensure that all characters are digits like so:
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CHECK (sn LIKE REPLICATE('[0-9]', LEN(sn)))
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The expression replicates the string [0-9] representing a single character that must be a digit as many times as the number of characters in the column sn. This means that for a lengthy string in the sn column, the pattern will be quite long. A more economical way to express the same idea is to use reverse logic. Another way to say that all characters must be digits is to say that no character can be something that is not a digit. This translates to the following predicate in the constraint:
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CHECK (sn NOT LIKE '%[^0-9]%')
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This pattern is much more economical compared with the one that applies positive logic, especially when dealing with long sn values. Note that both CHECK constraints provided here would allow an empty string as a serial number. If you do not want to allow empty strings, you need to add logic to the constraint.
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Misbehaving Subqueries
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I ve occasionally seen a very tricky programming error involving subqueries, and I ve even had the misfortune to introduce into production code myself. I ll rst describe the bug and then make recommendations for how you can avoid it. To demonstrate the bug, I use a table called Sales.MyShippers that you create and populate in the InsideTSQL2008 database by running the following code:
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IF OBJECT_ID('Sales.MyShippers', 'U') IS NOT NULL DROP TABLE Sales.MyShippers; CREATE TABLE Sales.MyShippers ( shipper_id INT NOT NULL, companyname NVARCHAR(40) NOT NULL, phone NVARCHAR(24) NOT NULL, CONSTRAINT PK_MyShippers PRIMARY KEY(shipper_id) );
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INSERT INTO VALUES(1, (2, (3,
Subqueries, Table Expressions, and Ranking Functions
Sales.MyShippers(shipper_id, companyname, phone) N'Shipper GVSUA', N'(503) 555-0137'), N'Shipper ETYNR', N'(425) 555-0136'), N'Shipper ZHISN', N'(415) 555-0138');
Suppose that you are asked to return the shippers from the Sales.MyShippers table that did not ship orders (in the Sales.Orders table) to customer 43. Examining the data, shipper 1 (Shipper GVSUA) is the only one that quali es. The following query is supposed to return the desired result:
SELECT shipper_id, companyname FROM Sales.MyShippers WHERE shipper_id NOT IN (SELECT shipper_id FROM Sales.Orders WHERE custid = 43);
Surprisingly, this query returns an empty set. Can you tell why Can you identify the elusive bug in my code Well, apparently the column in the Orders table holding the shipper ID is called shipperid (no underscore) and not shipper_id. The Orders table has no shipper_id column. Realizing this, you d probably expect the query to have failed because of the invalid column name. Sure enough, if you run only the part that was supposed to be a self-contained subquery, it does fail: Invalid column name shipper_id . However, in the context of the outer query, apparently the subquery is valid! The name resolution process works from the inner nesting level outward. The query processor rst looked for a shipper_id column in the Orders table, which is referenced in the current level. Not having found such a column name, it looked for one in the MyShippers table the outer level and found it. Unintentionally, the subquery became correlated, as if it were written as the following illustrative code:
SELECT shipper_id, companyname FROM Sales.MyShippers AS S WHERE shipper_id NOT IN (SELECT S.shipper_id FROM Sales.Orders AS O WHERE O.custid = 43);
Logically, the query doesn t make much sense, of course; nevertheless, it is technically valid. You can now understand why you got an empty set back. Unless you have no order for customer 43 in the Orders table, shipper some_val is obviously always found in the set (SELECT some_val FROM Sales.Orders WHERE custid = 43). And the NOT IN predicate always yields FALSE. This buggy query logically became a nonexistence query equivalent to the following illustrative code:
SELECT shipper_id, companyname FROM Sales.MyShippers WHERE NOT EXISTS (SELECT * FROM Sales.Orders WHERE custid = 43);
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