Class 8 - Functions in SQL Server

FUNCTIONS
What is function ?
A function in SQL Server can be defined primary as 2 types. User Defined Functions which is creating by user based on the requirement and System Defined Functions which was already created by Microsoft and provided for ready use.

These can be classified in other ways also :

The Transact-SQL programming language provides three types of functions:
• Rowset functions
Can be used like table references in an SQL statement.
• Aggregate functions
Operate on a collection of values but return a single, summarizing value.
• Scalar functions
Operate on a single value and then return a single value.

Deterministic and Nondeterministic Functions
All functions are deterministic or nondeterministic:
• Deterministic functions always return the same result any time they are called with a specific set of input values.
• Nondeterministic functions may return different results each time they are called with a specific set of input values.


USER DEFINED FUNCTIONS : When we come to User Defined Function again there are 3 types.
1) Scalar Function
2) Table Valued Function
3) Multi Statement Function

Scalar Functions
Scalare functions always returns single resultant value.
Syntax :
CREATE FUNCTION [ owner. ] fn_name ( [ { @parameter [ AS ] data_type }[ ,...n ] ] )
RETURNS data_type
[ AS ]
BEGIN
function_body
RETURN scalar_expression
END
Eg :
create function fn_studage (@id int) returns int
as
begin
declare @studage int
select @studage = datediff(year,dob,getdate()) from students where id = @id
return @studage
end

Inline Table-Valued Functions
Inline Table-Valued Functions return a resultset, as opposed to a single scalar value. A table valued function specifies the TABLE keyword in its RETURN clause. Its basic form is :
Syntax :
CREATE FUNCTION [ owner_name. ] fn_name ( [ { @parameter [ AS ] type } [ ,...n ] ])
RETURNS TABLE
[ AS ]
RETURN [ ( ] select-statement [ ) ]

An Inline Table-Valued Function created by this command:
CREATE FUNCTION datesales (@deadline as datetime)
RETURNS TABLE
AS
RETURN ( SELECT *
FROM sales
WHERE ord_date > @deadline)

and called by this sequence:
USE PUBS
GO
select * from datesales('09/13/1994')
will yield the following table:
stor_id ord_num ord_date qty payterms title_id
6380 6871 09/14/94 5 Net 60 BU1032
7067 D4482 09/14/94 10 Net 60 PS2091
7131 N914008 09/14/94 20 Net 30 PS2091
7131 N914014 09/14/94 25 Net 30 MC3021
8042 423LL922 09/14/94 15 ON invoice MC3021
8042 423LL930 09/14/94 10 ON invoice BU1032

Multi-statement Table-Valued Function
The final type of UDF is the Multi-statement Table-Valued Function. This UDS also returns a resultset, like the Inline variety UDF, but with a much more powerful result. The Multi-statement UFD can actually create a temporary table, specifying the fields, their type and characteristics. Now the scope of that temporary table is limited to the UDF in which it was defined, so when the UDF ends, the temporary table evaporates too. However, this can be a tremendously powerful technique to obtain or manipulate data.

The general form for the Multi-statement Table-Valued Function is:
CREATE FUNCTION [ owner_name. ] fn_name ( [ { @parameter [AS] type } [ ,...n ] ] )
RETURNS @return_variable TABLE < table_type_definition >
[ AS ]
BEGIN
function_body
RETURN
END
The following creates the datesales2 UDF:
CREATE FUNCTION datesales2 (@deadline datetime) RETURNS @table TABLE (stor_id varchar(6) null, ord_num varchar(8) null, ord_date datetime null, qty int, payterms varchar(20), title_id varchar(6))
AS
BEGIN
INSERT @table
SELECT *
FROM sales
WHERE ord_date > @deadline
RETURN
END
When the function is called by this sequence,
USE PUBS
GO
select * from datesales2('09/13/1994')
The following resultset is displayed and available. (It is the same set displayed in the Inline UDF, but created with the temporary table.)
stor_id ord_num ord_date qty payterms title_id
6380 6871 09/14/94 5 Net 60 BU1032
7067 D4482 09/14/94 10 Net 60 PS2091
7131 N914008 09/14/94 20 Net 30 PS2091
7131 N914014 09/14/94 25 Net 30 MC3021
8042 423LL922 09/14/94 15 ON invoice MC3021
8042 423LL930 09/14/94 10 ON invoice BU1032
Now these temporary tables by me combined, joined, with virtually any number created within the Multi-Tabled UDF, giving the user a very powerful tool for calculating and presenting data from the server in a way that truly leverages the effectiveness of writing code in the native language of SQL Server.

SYSTEM DEFINED FUNCTIONS :

FUNCTION EXPLANATION :

Function category Explanation
Configuration Functions : Returns information about the current configuration.
Cursor Functions : Returns information about cursors.
Date and Time Functions : Performs an operation on a date and time input value and returns either a string, numeric, or date and time value.
Mathematical Functions : Performs a calculation based on input values provided as parameters to the function, and returns a numeric value.
Metadata Functions : Returns information about the database and database objects.
Security Functions : Returns information about users and roles.
String Functions : Performs an operation on a string (char or varchar) input value and returns a string or numeric value.
System Functions : Performs operations and returns information about values, objects, and settings in Microsoft® SQL Server™.
System Statistical Functions : Returns statistical information about the system.
Text and Image Functions : Performs an operation on a text or image input values or column, and returns information about the value.


Configuration Functions :
@@REMSERVERReturns the name of the remote Microsoft® SQL Server™ database server as it appears in the login record.
Syntax
@@REMSERVER
Example :
CREATE PROCEDURE check_server
AS
SELECT @@REMSERVER

@@LANGUAGE
@@SERVERNAME

@@SERVICENAME
Example
SELECT @@SERVICENAME
Here is the result set:
------------------------------
MSSQLServer

@@SPID
@@MAX_CONNECTIONS
The actual number of user connections allowed also depends on the version of SQL Server installed and the limitations of your application(s) and hardware.
To reconfigure SQL Server for fewer connections, use sp_configure.
Examples
SELECT @@MAX_CONNECTIONS

@@VERSION

@@NESTLEVEL
Returns the nesting level of the current stored procedure execution (initially 0).

@@DATEFIRST
Returns the current value of the SET DATEFIRST parameter, which indicates the specified first day of each week: 1 for Monday, 2 for Wednesday, and so on through 7 for Sunday.
Syntax
@@DATEFIRST
Examples
SET DATEFIRST 5
SELECT @@DATEFIRST AS '1st Day', DATEPART(dw, GETDATE()) AS 'Today'
Here is the result set. Counting from Friday, today (Saturday) is day 2.
1st Day Today
---------------- --------------
5 2



2. Cursor Functions
@@CURSOR_ROWS
@@CURSOR_STATUS
@@FETCH_STATUS

3. Date and Time Functions
Datepart Abbreviations
Year yy, yyyy
Quarter qq, q
Month mm, m
dayofyear dy, y
Day dd, d
Week wk, ww
Hour hh
minute mi, n
second ss, s
millisecond ms

DATEADD
Eg : SELECT DATEADD(day, 21, pubdate) AS timeframe fROM titles

DATEDIFF
SELECT DATEDIFF(day, pubdate, getdate()) AS no_of_days
FROM titles

DATENAMESELECT DATENAME(month, getdate()) AS 'Month Name' = February

DATEPARTSELECT DATEPART(month, GETDATE()) AS 'Month Number' = 2

DAY SELECT DAY('03/12/1998') AS 'Day Number'

MONTHSELECT MONTH('03/12/1998') AS 'MONTH Number'

YEARSELECT YEAR('03/12/1998') AS 'YEAR Number'

GETDATE()SELECT GETDATE()

4. Mathematical Functions
CEILING Returns the smallest integer greater than, or equal to, the given numeric expression.
Examples
This example shows positive numeric, negative, and zero values with the CEILING function.
SELECT CEILING($123.45), CEILING($-123.45), CEILING($0.0)
GO
Here is the result set:
--------- --------- -------------------------
124.00 -123.00 0.00

FLOORReturns the largest integer less than or equal to the given numeric expression.
Examples
This example shows positive numeric, negative numeric, and currency values with the FLOOR function.
SELECT FLOOR(123.45), FLOOR(-123.45), FLOOR($123.45)
The result is the integer portion of the calculated value in the same data type as numeric_expression.
--------- --------- -----------
123 -124 123.0000

TRIGNOMETRY :
SIN
COS
TAN
COT

5. Metadata Functions
@@PROCIDReturns the stored procedure identifier (ID) of the current procedure
SELECT @@PROCID AS 'ProcID'

OBJECTPROPERTYIF OBJECTPROPERTY ( object_id('authors'),'ISTABLE') = 2
print 'Authors is a table'

DB_IDReturns the database identification (ID) number.

DB_NAMEReturns the database name.
Ex :
SELECT dbid, DB_NAME(dbid) AS DB_NAME
FROM sysdatabases

OBJECT_ID


6. Security Functions
USER
USER_ID
SUSER_NAME : EG :select SUSER_NAME(0X01)
SUSER_SID : EG : SELECT SUSER_SID('sa')

7. String Functions
LTRIMReturns a character expression after removing leading blanks.
select ltrim(' venkat')

RTRIM
Returns a character string after truncating all trailing blanks.

UPPERReturns a character expression with lowercase character data converted to uppercase.
select upper('venkat')

LOWERReturns a character expression with UPPER character data converted to lowercase.

LENReturns the number of characters, rather than the number of bytes, of the given string expression, excluding trailing blanks.

LEFTReturns the part of a character string starting at a specified number of characters from the left.
Ex : left(‘venkat’,3)

RIGHTReturns the part of a character string starting at a specified number of characters from the right.
Ex : Right(‘venkat’,3)

REPLACEReplaces all occurrences of the second given string expression in the first string expression with a third expression.
Examples
This example replaces the string cde in abcdefghi with xxx.
SELECT REPLACE('abcdefghicde','cde','xxx')


8. System Functions
CASE
CAST and CONVERTExplicitly converts an expression of one data type to another. CAST and CONVERT provide similar functionality.

CAST : SELECT SUBSTRING(title, 1, 30) AS Title, ytd_sales
FROM titles
WHERE CAST(ytd_sales AS char(20)) LIKE '3%'

CONVERT : SELECT SUBSTRING(title, 1, 30) AS Title, ytd_sales
FROM titles
WHERE CONVERT(char(20), ytd_sales) LIKE '3%'

ISNULLCOALESCE
CURRENT_USER
HOST_ID
HOST_NAME
Eg : CREATE TABLE Orders
(OrderID INT PRIMARY KEY,
Workstation NCHAR(30) NOT NULL DEFAULT HOST_NAME())

@@IDENTITY
ISNUMERIC
@@row_count
SCOPE_IDENTITY
SERVERPROPERTY
eg : SELECT SERVERPROPERTY('servername'),
SELECT SERVERPROPERTY('productlevel')

SYSTEM_USER

@@TRANCOUNT

USER_NAME

System Statistical Functions
@@CONNECTIONSReturns the number of connections, or attempted connections, since Microsoft® SQL Server™ was last started.

@@PACK_RECEIVEDReturns the number of input packets read from the network by Microsoft® SQL Server™ since last started.

@@CPU_BUSYReturns the time in milliseconds (based on the resolution of the system timer) that the CPU has spent working since Microsoft® SQL Server™ was last started.

@@PACK_SENTReturns the number of output packets written to the network by Microsoft® SQL Server™ since last started.

@@TOTAL_ERRORSReturns the number of disk read/write errors encountered by Microsoft® SQL Server™ since last started.

9. Text and Image FunctionsPATINDEX
TEXTPTR
TEXTVALID

Class 7 - Views in SQL Server

VIEW IN SQL SERVER 2000
Views are nothing but saved SQL queries. Suppose you have written a query by using multiple SQL statements to view the data. But it may require that watching the data from these tables whenever required. For this you don’t need to write all these queries every time, instead you can save it as a view. View doesn’t contain any data, it is just a query.

CREATE A VIEW
This example creates a view with a simple SELECT statement. A simple view is helpful when a combination of columns is queried frequently.
CREATE VIEW titles_view
AS
SELECT title, type, price, pubdate
FROM titles
GO

JOINS :
Views can be written by using multiple tables with help of joins. There are different joins available in SQL Server. As per the requirement we can choose join to use in the queries for view.

INNER
LEFT OUTER
RIGHT OUTER
FULL
CROSS
SELF
CARTISAN

Eg : Create view ABCD_View
AS
Select a.Col1, a.col2, b.col1, b.col2
from Table_A inner join Table_B
on a.Col1 = b.Col2


Some Arguments about Views in Sql Server 2000 : •
You can create views only in the current database. However, the tables and views referenced by the new view can exist in other databases or even other servers if the view is defined using distributed queries.
• A view can reference a maximum of 1,024 columns.
• A View can be used as a security mechanism like we can given permissions for the users also.
• View names must follow the rules for identifiers and must be unique for each user. Additionally, the name must not be the same as any tables owned by that user.
• You can build views on other views and on procedures that reference views. Microsoft® SQL Server™ 2000 allows views to be nested up to 32 levels.
• You cannot associate rules or DEFAULT definitions with views.
• You cannot associate AFTER triggers with views, only INSTEAD OF triggers.
• The query defining the view cannot include the ORDER BY, COMPUTE, or COMPUTE BY clauses or the INTO keyword.
• You cannot define full-text index definitions on views.
• You cannot create temporary views, and you cannot create views on temporary tables.
• Views or tables participating in a view created with the SCHEMABINDING clause cannot be dropped, unless the view is dropped or changed so that it no longer has schema binding. In addition, ALTER TABLE statements on tables that participate in views having schema binding will fail if these statements affect the view definition.
• When a view is created, the name of the view is stored in the sysobjects table.
• If the new table (or view) structure changes, then the view must be dropped and recreated.

View can be createD by using following options for security and performance purposes.

WITH CHECK OPTIONForces all data modification statements executed against the view to adhere to the criteria set within select_statement. When a row is modified through a view, the WITH CHECK OPTION ensures the data remains visible through the view after the modification is committed.
Eg :
CREATE VIEW CAonly
AS
SELECT au_lname, au_fname, city, state
FROM authors
WHERE state = 'CA'
WITH CHECK OPTIONGO

WITH ENCRYPTIONIndicates that SQL Server encrypts the system table columns containing the text of the CREATE VIEW statement. Using WITH ENCRYPTION prevents the view from being published as part of SQL Server replication.
Eg :
CREATE VIEW CAonly
AS
SELECT au_lname, au_fname, city, state
FROM authors
WHERE state = 'CA'
WITH ENCRYPTION
GO

SCHEMABINDINGBinds the view to the schema. When SCHEMABINDING is specified, the select_statement must include the two-part names (owner.object) of tables, views, or user-defined functions referenced.
Views or tables participating in a view created with the schema binding clause cannot be dropped unless that view is dropped or changed so that it no longer has schema binding. Otherwise, SQL Server raises an error. In addition, ALTER TABLE statements on tables that participate in views having schema binding will fail if these statements affect the view definition.

Use built-in functions within a view : This example shows a view definition that includes a built-in function. When you use functions, the derived column must include a column name in the CREATE VIEW statement.
CREATE VIEW categories (category, average_price)
AS
SELECT type, AVG(price)
FROM titles
GROUP BY type
GO