SQL Server - Bài 6

SQL Server - Bài

Stored Procedures &

Introduction to SQL Batch Processing

Batch

Individual SQL

commands

Grouped to form a batch

Compiled

as single execution plan

Use PubsSelect * from authorsUpdate authors

set phone= '890 451-7366‘where au_lname= 'White'Go

 Understanding the concepts of batch and batch

processing

 T-SQL Programming

 Define and assign variables

 Cursors for data retrieval

 Control statements

 Write SQL statements using SQL Server basic functions

 Use basic functions in a query

 Implementing Stored Procedures

 Implementing User-Defined Functions

Assigning values to variables

 SET statement

SET @local_variable name = value

 SELECT statement

SELECT @local_variable name = value

SELECT CUSTOMERID,COMPANYNAME FROM CUSTOMERS

SQL Server supports two types of variables in T-SQL

@@global_variable

@local_variable

List of Global variables

@@CONNECTIONS Number of connections made to the server

since it was last started

@@CPU_BUSY Number of milliseconds the system has been

processing since SQL Server was started

@@CURSOR_ROWS Number of rows in the most recently opened

cursor

@@ERROR Error number of the last T-SQL error

@@FETCH_STATUS 0 if the last fetch status was successful

-1 if there was an error

List of Global variables (2)

@@IDENTITY Last inserted identity value

@@LANGUAGE Name of the language currently in use

@@MAX_CONNECTIONS Maximum number of concurrent

connections that can be made

@@ROWCOUNT Number of rows affected by most

recent SQL Statement

@@SERVERNAME Name of local server

@@SERVICENAME Name of the SQL Service on this

computer

@@TIMETICKS Number of microseconds per tick on

the current computer

@@TRANSCOUNT Number of transaction open on the

current connection

Cursors to Retrieve Data

 Allowing positioning at specific rows of the result set

 Retrieving one row or block of rows from the current

position in the result set

 Supporting data modifications to the rows at the current position in the result set

 Supporting different levels of visibility for changes made

by other users to the data in the result set

 Providing access to the data in a result set for T-SQL statements in scripts, stored procedures, and triggers

Cursor Implementations

 Transact-SQL Server Cursors

 Used in scripts, stored procedures, and triggers

 Implemented on the server

 API Server Cursors

 Implemented on the server but managed by API cursor functions (OLE DB, ODBC, DB-Library)

 Client Cursors

 Entire result set is cached on client and all cursor

operations are performed against this cached set

Working with T-SQL Server Cursors

 Declare the cursor

 Populate the cursor

 Retrieve (fetch) the result set

 First, Next, Prior, Last, Absolute n, Relative n

 Optional: update or delete a row

 Close the cursor

 Free resources allocated to the cursor

Control Statements

Control Statements Contd…

We can execute different

sets of SQL statements based on

Example

WHILE construct

We can execute a SQL statement or a

block of statements based on some condition

SET price = price * 2

SELECT MAX(price) FROM titles

IF (SELECT MAX(price) FROM titles) > $50

GOTO keyword

GOTO:

We can change the flow of execution to a specified location

(label) The statements after GOTO keyword are skipped and the execution process continues at the specified label in the GOTO statement

Syntax:

GOTO label

RETURN: We can use RETURN at any point to exit from a block, procedure Statements after the RETURN statement are not executed

Syntax:

RETURN [ integer_expression ]

WHEN expression1 THEN expression1

[[WHEN expression2 THEN expression2] […]]

[ELSE expression]

END

 Example:

SELECT au_fname, au_lname,CASE state

WHEN 'OR' THEN 'Oregon'

Multi column updates using CASE

be updated using one command in this manner

 Understanding the concepts of batch and batch

processing

 T-SQL Programming

 Define and assign variables

 Cursors for data retrieval

 Control statements

 Write SQL statements using SQL Server basic functions

 Use basic functions in a query

 Implementing Stored Procedures

 Implementing User-Defined Functions

Stored Procedures

 Main ideas

 move the processing as close to the data as possible

 Move into a batch that has been stored with a name so it can be pre-compiled

Creating a Stored Procedure

Modifying a Stored Procedure

ALTER PROCEDURE GetSubjects AS

SELECT *

Deleting a Stored Procedure

DROP PROCEDURE dbo.GetSubjects

Executing a Stored Procedure

 Local stored procedures

 Understanding the concepts of batch and batch

processing

 T-SQL Programming

 Define and assign variables

 Cursors for data retrieval

 Control statements

 Write SQL statements using SQL Server basic functions

 Use basic functions in a query

 Implementing User-Defined Functions

 embed complex logic within a query.

 create new functions for complex expressions

 Three distinct types

 Scalar functions that return a single value

 Updateable inline table functions similar to views

 Multi-statement table functions that build a result set with code

Creating a Scalar Function

Creating a Inline Table Function

Creating a Multi-statement table function

Modifying a Scalar Function

Modifying a Inline Table Functions

Modifying a Multi-statement Table Function

Summary