c# barcode generator source code Figure 11-42. Changing the NULL to a value if the value is a NULL in Font

Encoder PDF417 in Font Figure 11-42. Changing the NULL to a value if the value is a NULL

Figure 11-42. Changing the NULL to a value if the value is a NULL
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ISNUMERIC()
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This final system function tests the value within a column or variable and ascertains whether it is numeric or not. The value returned is 0, or false, for an invalid number, or 1 for true if the test is okay and can convert to a numeric.
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CHAPTER 11 T-SQL ESSENTIALS
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Note
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Currency symbols such as and $ will also return 1 for a valid numeric value.
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Try It Out: ISNUMERIC()
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1. Our first example to demonstrate ISNUMERIC() defines a character variable and contains alphabetic values. This test fails, as shown in Figure 11-43. DECLARE @IsNum char(10) SET @IsNum = 'Robin ' SELECT ISNUMERIC(@IsNum)
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Figure 11-43. Checking whether a value is a number and finding out it is not 2. This second example places numbers and spaces into a char field. The ISNUMERIC() test ignores the spaces, provided that there are no further alphanumeric characters. DECLARE @IsNum char(10) SET @IsNum = '1234 ' SELECT ISNUMERIC(@IsNum) Figure 11-44 shows the results of running this code.
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Figure 11-44. Finding out a value is numeric
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RAISERROR
Before we look at handling errors, you need to be aware of what an error is, how it is generated, the information it generates, and how to generate your own errors when something is wrong. The T-SQL command RAISERROR allows us as developers to have the ability to produce our own SQL Server error messages when running queries or stored procedures. We are not tied to just using error messages that come with SQL Server; we can set up our own messages and our own level of severity for those messages. It is also possible to determine whether the message is recorded in the Windows error log or not. However, whether we wish to use our own error message or a system error message, we can still generate an error message from SQL Server as if SQL Server itself raised it. Enterprise environments typically experience the same errors on repeated occasions, since they employ SQL Server in very specific ways depending on their business model. With this in mind, attention to employing RAISERROR can have big benefits by providing more meaningful feedback as well as suggested solutions for users.
CH A PT ER 1 1 T -SQ L ES SEN TI ALS
By using RAISERROR, the whole SQL Server system acts as if SQL Server raised the error, as you have seen within this book. RAISERROR can be used in one of two ways; looking at the syntax will make this clear. RAISERROR ({msg_id|msg_str} {,severity,state} [,argument [ ,...n ] ]) [WITH option [ ,...n ]] You can either use a specific msg_id or provide an actual output string, msg_str, either as a literal or a local variable defined as string-based, containing the error message that will be recorded. The msg_id references system and user-defined messages that already exist within the SQL Server error messages table. When specifying a text message in the first parameter of the RAISERROR function instead of a message ID, you may find that this is easier to write than creating a new message: RAISERROR('You made an error', 10, 1) The next two parameters in the RAISERROR syntax are numerical and relate to how severe the error is and information about how the error was invoked. Severity levels range from 1 at the innocuous end to 25 at the fatal end. Severity levels of 2 to 14 are generally informational. Severity level 15 is for warnings, and levels 16 or higher represent errors. Severity levels from 20 to 25 are considered fatal, and require the WITH LOG option, which means that the error is logged in the Windows Application Event log and the SQL Error log and the connection terminated; quite simply, the stored procedure stops executing. The connection referred to here is the connection within Query Editor, or the connection made by an application using a data access method like ADO.NET. Only for a most extreme error would we set the severity to this level; in most cases, we would use a number between 1 and 18. The last parameter within the function specifies state. Use a 1 here for most implementations, although the legitimate range is from 1 to 127. You may use this to indicate which error was thrown by providing a different state for each RAISERROR function in your stored procedure. SQL Server does not act on any legitimate state value, but the parameter is required. A msg_str can define parameters within the text. By placing the value, either statically or via a variable, after the last parameter that you define, msg_str replaces the message parameter with that value. This is demonstrated in an upcoming example. If you do wish to add a parameter to a message string, you have to define a conversion specification. The format is % [[flag] [width] [. precision] [{h | l}]] type The options are as follows: flag: A code that determines justification and spacing of the value entered: - (minus): Left-justify the value. + (plus): The value shows a + or a sign. 0: Prefix the output with zeros. #: Preface any nonzero with a 0, 0x, or 0X, depending on the formatting. (blank): Prefix with blanks. width: The minimum width of the output. precision: The maximum number of characters used from the argument.
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