2 designing tables

Copyright 2014 © Ram Kedem. All rights reserved. Not to be reproduced without written consent
Working with System Tables
•System Views are predefined Microsoft created views for extracting SQL Server metadata.
•Expand Database => Views => System Views

Information Schema
•The first group of System Views belongs to the Information Schema set.
•Information Schema is an ANSI specification for obtaining metadata.
CREATE TABLE MyTable
(
Col1 int,
Col2 varchar(10),
Col3 datetime
)
GO
SELECT *
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME = 'MyTable' ;
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'MyTable'

Catalog Views
•New in SQL 2005 are Catalog Views. Microsoft recommends them as the most general interface to the catalog metadata.
SELECT *
FROM sys.tables
SELECT *
FROM sys.columns INNER JOIN sys.tables ON
sys.tables.object_id = sys.columns.object_id
WHERE sys.tables.name = 'MyTable'

Dynamic Management Views
•The last groups of views are called Dynamic Management views, or DM.
•They are used to gather statistics stored in memory but not persistent on disk such as thread information, memory usage, and connection details.

SQL Server Schema
•Schemas are used to logically group tables, procs, views together, all employee related objects in the employee schema etc.independent entity- a container of objects distinct from the user who created those objects.
•Previously (2000), the terms ‘user’ and ‘database object owner’ meant one and the same thing, but now the two are separate.
CREATE SCHEMA MySchema

Object Name Resolution
•Users can have a default schema assigned
•Users with no defined default schema will have dbo as their default schema
•If the schema name is omitted, rules apply to how the name will be resolved by the following sequence :
•First search is in the user's default schema
•If not found, the dbo schema will be searched also
• Every schema has an owner (user) As long as a user own some schema he cannot be deleted.

Temporary Tables
•Session Temporary Tables
•Session temporary tables are only visible to their creators in the same session and same scope or sub-scope
•Created with a # prefix
•Dropped when the user disconnects or when out of scope
•Global Temporary Tables
•Global temporary tables are visible to all users
•Created with a ## prefix
•Deleted when all users referencing the table disconnect

Temporary Tables
-- Create sample table and populate it with values
CREATE TABLE #temp_tbl
( Number int PRIMARY KEY,
Name varchar(25));
INSERT INTO #temp_tbl
VALUES (1, 'Ram')
INSERT INTO #temp_tbl
VALUES (2, 'Kedem')
-- Query the table
SELECT * FROM #temp_tbl;
GO
-- Disconnect and reconnect, then try to re execute query
SELECT * FROM #temp_tbl;
GO

Working with IDENTITY
•Property of a column
•Specify a seed and an increment (Default seed and increment are both 1)
CREATE TABLE employees
(employeeID int identity(1,1) PRIMARY KEY,
lastName varchar(25),
hireDate date default getdate(),
salary decimal(8,2) default 15000)
-- Populate the table with 2 rows
INSERT INTO employees
VALUES ('David' , default, default)
-- Check the identity values added
SELECT * FROM employees;
-- Try to insert a specific value for employeeID. This will fail
INSERT INTO employees
VALUES (1, 'Tamar' , '1995-07-20' , default)

SET IDENTITY_INSERT ON
•Having the IDENTITY property on a column does not in itself ensure that the column is unique.
•SET IDENTITY_INSERT ON can be used to allow the user to insert values into the column with the IDENTITY property instead of having it autogenerated.
DROP TABLE emps ;
GO
CREATE TABLE emps
(emp_id int IDENTITY(1,1) ,
emp_name varchar(25))
GO
INSERT INTO emps
VALUES ('Yossi' )

SET IDENTITY_INSERT ON
•SET IDENTITY_INSERT emps ON
•INSERT INTO emps (emp_id , emp_name)
•VALUES (1,'Moshe' )
•-- Error : An explicit value for the identity -- column in table possible only when
•-- Specified when a column list is used
•-- and IDENTITY_INSERT is ON.
•INSERT INTO emps
•VALUES (2,'Avi' )
•SET IDENTITY_INSERT emps OFF
•
•INSERT INTO emps (emp_id , emp_name)
•VALUES (2,'Tomer' )
•SELECT * FROM emps ;

Unique Identifiers
•NEWID() randomly generates a guaranteed unique value based on the identification number of the server's network card plus a unique number from the CPU clock
•Each process involved can create its own values and know that they will not clash with the values created by another process.
•The major advantage of using GUIDs is that they are unique across all space and time.
•This comes in handy if you're consolidating records from multiple SQL Servers into one table, as in a data warehousing situation.
•GUIDs are also used heavily by SQL Server replication to keep track of rows when they're spread out among multiple SQL Servers.

Unique Identifiers
•The main disadvantage to using GUIDs as key values is that they are BIG. At 16 bytes a pop, they are one of the largest datatypes in SQL Server.
•Indexes built on GUIDs are going to be larger and slower than indexes built on IDENTITY columns, which are usually ints (4 bytes).

Unique Identifiers
DROP TABLE uniqueid_tab
CREATE TABLE uniqueid_tab
(product_id UNIQUEIDENTIFIER ,
product_name varchar(25))
INSERT INTO uniqueid_tab
VALUES ( NEWID() , 'Windows-7')
VALUES ( NEWID() , 'Windows-XP')
VALUES ( NEWID() , 'Windows Server 2003')
SELECT * FROM uniqueid_tab ;

Unique Identifiers
•NEWID() randomly generates a guaranteed unique value based on the identification number of the server's network card plus a unique number from the CPU clock
•Each process involved can create its own values and know that they will not clash with the values created by another process.
•The major advantage of using GUIDs is that they are unique across all space and time.
•This comes in handy if you're consolidating records from multiple SQL Servers into one table, as in a data warehousing situation. GUIDs are also used heavily by SQL Server replication to keep track of rows when they're spread out among multiple SQL Servers.
•The main disadvantage to using GUIDs as key values is that they are BIG. At 16 bytes a pop, they are one of the largest datatypes in SQL Server.
•Indexes built on GUIDs are going to be larger and slower than indexes built on IDENTITY columns, which are usually ints (4 bytes).
•=, <>, <, >, <=, >= are supported along with NULL and NOT NULL checking
•IDENTITY cannot be used
•New values from NEWID() function

Sequences
CREATE SEQUENCE dbo.BookingID AS INT
START WITH 1000
INCREMENT BY 1;
GO
/*
CREATE SEQUENCE [schema_name . ] sequence_name
[ AS [ built_in_integer_type | user-defined_integer_type ] ]
[ START WITH <constant> ]
[ INCREMENT BY <constant> ]
[ { MINVALUE [ <constant> ] } | { NO MINVALUE } ]
[ { MAXVALUE [ <constant> ] } | { NO MAXVALUE } ]
[ CYCLE | { NO CYCLE } ]
[ { CACHE [ <constant> ] } | { NO CACHE } ]
[ ; ]
*/

Sequences
CREATE TABLE usa_booking
(booking_id int
CONSTRAINT usa_booking_id DEFAULT (NEXT VALUE FOR dbo.BookingID),
booking_description varchar(25))
CREATE TABLE europe_booking
(booking_id int
CONSTRAINT europe_booking_id DEFAULT (NEXT VALUE FOR dbo.BookingID),
CREATE TABLE china_booking
(book_id int
CONSTRAINT china_booking_id DEFAULT (NEXT VALUE FOR dbo.BookingID),

Sequences
INSERT INTO usa_booking (booking_description)
VALUES ('Booking 1')
INSERT INTO europe_booking (booking_description)
INSERT INTO china_booking (booking_description)
SELECT * , 'USA' as 'BookingLocation'FROM usa_booking
UNION ALL
SELECT * , 'Europe' as 'BookingLocation'FROM europe_booking
UNION ALL
SELECT * , 'China' as 'BookingLocation'FROM china_booking

2 designing tables

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2 designing tables