barcode generator in vb.net codeproject Using the CREATE FUNCTION Statement in Software

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Using the CREATE FUNCTION Statement
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Now let s take a look at the statement used for creating an SQL-invoked function. As you can see in the following syntax, a function contains a few more elements than a procedure: CREATE FUNCTION <function name> ( [ <parameter declaration> [ { , <parameter declaration> } . . . ] ] ) RETURNS <data type> [ <routine characteristic> . . . ] [ STATIC DISPATCH ] <routine body> As with procedures, you must first provide a name for your function, followed by the parameter declaration list. Functions support only input parameters, and if none are provided, you must still use the parentheses. If more than one input parameter is provided, you must separate them using commas. Following the parameter declarations is the RETURNS clause. You must provide the data type for the value that s returned by the function. After that, you can include any of the optional routine characteristics, depending on what options your SQL implementation supports. Next is the STATIC DISPATCH clause. You must specify this clause if you use a user-defined type, a reference data type, or an array data type. Because these types are all beyond the scope of this book, you do not need to be concerned with the STATIC DISPATCH clause at this time. The last thing that you must include in the procedure definition is, of course, the routine body. As with procedures, these are the SQL statements that make up the core of your procedure. However, there is one additional element you ll find in the routine body that is not included in a procedure s routine body a RETURN statement (not to be confused with the RETURNS clause). The RETURN statement specifies the value that will be returned by the function. Later in this chapter, in the Create SQL-Invoked Functions section, I ll discuss the RETURN statement and other elements of the CREATE FUNCTION statement in more detail.
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Create SQL-Invoked Procedures
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Now that you have an overview of SQL-invoked routines and the syntax used to create them, let s take a closer look at how to create SQL-invoked procedures. A procedure can perform most functions that you can perform by using SQL statements directly. In addition, procedures can be used to pass parameters and define variables, which we ll get into later in this chapter. For now, let s look at a procedure at its most basic, one that includes no parameters or special types of SQL statements.
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CD_INVENTORY CD_TITLE: VARCHAR(60) Famous Blue Raincoat Blue Past Light Out of Africa Fundamental Blues on the Bayou Kojiki CD_TYPE_ID: CHAR(4) FROK CPOP NEWA STRK NPOP BLUS NEWA CD_STOCK: INT 19 28 6 8 10 11 10
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CD_TYPES CD_TYPE_ID: CHAR(4) FROK CPOP NEWA CTRY STRK BLUS JAZZ CD_TYPE_NAME: CHAR(20) Folk Rock Classic Pop New Age Country Soundtrack Blues Jazz
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Figure 13-1
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Using procedures to access the CD_INVENTORY and CD_TYPES tables
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Suppose you need to query the data in the CD_INVENTORY and CD_TYPES tables shown in Figure 13-1. You want your query results to return the CD names and number in stock for all New Age CDs. To view this information, you can create a SELECT statement that joins the two tables, as shown in the following example:
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SELECT FROM WHERE AND CD_TITLE, CD_STOCK CD_INVENTORY i, CD_TYPES t i.CD_TYPE_ID = t.CD_TYPE_ID CD_TYPE_NAME = 'New Age';
Of course, every time you want to view this information, you would have to recreate the SELECT statement. However, another option is to store the SELECT statement within the schema. That way, all you need to do is call that statement whenever you want to view the New Age CDs. One way to store the SELECT statement is within a view definition:
CREATE VIEW NEW_AGE AS SELECT CD_TITLE, CD_STOCK FROM CD_INVENTORY i, CD_TYPES t WHERE i.CD_TYPE_ID = t.CD_TYPE_ID AND CD_TYPE_NAME = 'New Age';
Once the view is created, you can use a SELECT statement to call the view, as shown in the following statement:
SELECT * FROM NEW_AGE;
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