Trigger& Stored procedures and functions are and difference between the three
Triggers are special stored procedures, stored procedure requires procedure call, and will a you said function is a custom function bar, the function is to produce an output according to input from only input-output relationship defined by the user to defined. When used in the trigger? Require the system to operate automatically under certain related tasks, such as buying out the products according to the number of automatic deduction of input inventory of the product. When to use stored procedures? Stored procedure is the procedure, it is the result of the SQL syntax checking and compiling statements, so to run particularly fast.
Stored procedures and user-defined function of specific differences
Look at the definition:
Stored procedure
Stored procedure can make the management of the database, and display information on the database and its user work much easier. Stored procedure is SQL statements and optional control-flow statements pre-compiled collection of a name to store and handle as a unit. Stored procedure is stored in the database, the application can be invoked by an execution, but also allows the user to declare variables, conditional execution, and other powerful programming features.
Stored procedures can contain program flow, logic, and database queries. They can accept parameters, output parameters, return single or multiple result sets and return values.
You can use SQL statements for any purpose to use stored procedures, it has the following advantages:
In a single stored procedure can execute a series of SQL statements.
Stored procedure from within their own reference other stored procedures, which can simplify a complex statement.
When stored procedure is created that is compiled on the server, so the implementation of a single SQL statement is faster than them.
User-defined function
Function by one or more Transact-SQL statements consisting of subroutines, can be used to encapsulate code for reuse. Microsoft? SQL Server? 2000 does not limit users to Transact-SQL language is defined as part of the built-in function, but rather allows the user to create their own user-defined function.
CREATE FUNCTION statement can be used to create, use ALTER FUNCTION statement, modified, and the use DROP FUNCTION to remove user-defined function statement. Each perfectly legitimate user-defined function name (database_name.owner_name.function_name) must be unique.
Must be granted CREATE FUNCTION permissions to create, modify, or remove user-defined function. Not the owner of the user using the Transact-SQL statement in a function, you must first give the user the appropriate permissions granted to the function. To create or change in the CHECK constraint, DEFAULT clause, or computed column definition of user-defined functions referenced in the table, must also have the function of the REFERENCES permission.
In the function, leading to delete the statement differentiated treatment and continue as a trigger or stored procedure in such models in the next statement in the Transact-SQL error. In the function, the error would lead to stop the implementation of the function. Next, the operation led to wake-up call to stop the function of the statement.
The type of user-defined function
SQL Server 2000 supports three user-defined function:
Scalar function inline table-valued function statement table-valued function over user-defined functions with zero or more input parameters and returns a scalar value or a table. Function can have up to 1024 input parameters. When the function of the parameters have default values, call the function must specify the default DEFAULT keyword to obtain the default value. This behavior is different from the stored procedure parameters with default values, and in the course of these stores also means that the function is omitted the default value is omitted. User-defined function does not support output parameters.
Scalar function returns the RETURNS clause defines the types of individual data values. You can use all the scalar data types, including bigint and sql_variant. Does not support the timestamp data type, user-defined data types and non-scalar type (such as table or cursor). In the BEGIN ... END block that contains the main function defined to return the value of the Transact-SQL statement series. In addition to the return type can be text, ntext, image, cursor, and timestamp in addition to any data type.
Table values function returns the table. For inline table-valued functions, no
table is a single SELECT statement result set. For multi-statement table-valued functions, in BEGIN ... END block that contains the main function defined in TRANSACT-SQL statements, these statements generate rows and rows can be inserted to return to the table. The inline table-valued function of more information, please see the embedded user-defined function. The table-valued function of more information, please see the returns table data type of user-defined function.
BEGIN ... END statement block can not have any side effects. Function side effects are a function outside the scope (such as database table changes) of the resource state of any permanent change. Function statement, can only change is a function of the local objects (such as local cursors or local variables) changes. Can not function in the implementation of the operation include: changes to the database table, not the function of the local cursor to operate on, send e-mail, try to modify the directory, and generate the result set returned to the user.
Function valid statement types are:
DECLARE statement, the statement can be used to define the function local data variables and cursors.
Assignment for the function of local objects, such as the use of SET to the scalar and table local variables assignments.
Cursor operation that references in the function declaration, open, close and release the local cursor. FETCH statement does not allow use of the data returned to the client. FETCH statement only allows the use of local variables through the INTO clause to assign.
Control flow statement.
SELECT statement that contains a list with the choice of expression, which gives expression to the value of the function of local variables.
INSERT, UPDATE and DELETE statements, these statements modify the functions of the local table variable.
EXECUTE statement, the statement calls extended stored procedure.
Functions specified in the query number of times the actual implementation of the optimized execution plan generated may be different between. Example for the WHERE clause subquery wake function calls. Subquery and its function, the frequency of execution chosen by the optimizer access path to another.
User-defined function will be allowed to return different data for each call built-in functions. User-defined functions are not allowed to use the following built-in functions:
Structure binding function
CREATE FUNCTION support SCHEMABINDING clause, which can function to bind to any object that it references (such as tables, views, and other user-defined function) structure. Attempt to bind the function structure of any object referenced by the implementation of ALTER or DROP will fail.
Must meet the following conditions in order to specify in the CREATE FUNCTION SCHEMABINDING:
Referenced in the function of all views and user-defined function must be bound to the framework.
This function must be referenced with the function of all objects in the same database. Must use a part or two parts by the name to refer to the object.
Must have reference to the function of all objects (tables, views, and user-defined functions) REFERENCES permission.
ALTER FUNCTION can be used to delete schema binding. ALTER FUNCTION statement specified by the function without the WITH SCHEMABINDING to redefine the function.
Call user-defined function
When calling a scalar user-defined function, must provide at least two-part name:
SELECT *, MyUser.MyScalarFunction () FROM MyTable
Can constitute a part of the name calling table-valued function:
SELECT * FROM MyTableFunction ()
However, when the call returns a table SQL Server built-in function, must be the prefix:: add to the function name:
SELECT * FROM:: fn_helpcollations ()
Transact-SQL statement can be permitted in the function returns data type of expression the same location where any reference to scalar functions, including the calculation of columns and CHECK constraint definitions. For example, the following statement creates a simple function to return decimal:
CREATE FUNCTION CubicVolume - Input dimensions in centimeters (@ CubeLength decimal (4,1), @ CubeWidth decimal (4,1), @ CubeHeight decimal (4,1)) RETURNS decimal (12,3) - Cubic Centimeters.ASBEGIN RETURN (@ CubeLength * @ CubeWidth * @ CubeHeight) END
Integer expression can then be allowed any place (such as the calculation of the table columns) to use the function:
CREATE TABLE Bricks (BrickPartNmbr int PRIMARY KEY, BrickColor nchar (20), BrickHeight decimal (4,1), BrickLength decimal (4,1), BrickWidth decimal (4,1), BrickVolume AS (dbo.CubicVolume (BrickHeight, BrickLength, BrickWidth)))
dbo.CubicVolume is returned to the user-defined scalar function of an example. RETURNS clause defines the value returned by the function of the scalar data types. BEGIN ... END block that contains one or more of the implementation of the function of the Transact-SQL statement. Each of the function RETURN statement must have a parameter, can return with the RETURNS clause specified data type (or hidden into the type specified in the RETURNS data type) of data values. RETURN parameter is the function return value
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