Designing and Creating an SQL Server Database

Designing and Creating a
Database – Part 2
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Objectives
• Learn basic relational database design principles
• Create a SQL Server database based on sound design
principles
• Build tables using the SQL Server Management Studio
designers
• Learn about SQL Server data types
• Create constraints, triggers, and indexes
• Create a database diagram and define relationships to
enforce referential integrity


Agenda
• Relational Database Design Principles
• Implementing Database Design


Database Storage
• Pages
• The minimum unit of storage: 8 KB
• Maximum size of a row
• Except long values: text, ntext, image, varchar(max), nvarchar(max),
varbinary(max)
• 8060 bytes, after deducting space for overhead

• Extents
• 8 pages per Extent
• New objects at first stored in spare pages in existing extents


Database Storage
• Files
• .MDF, .NDF, .LDF
• The transaction log ensures data integrity
• Filegroups
• Can locate data or indexes in additional files and on
separate devices (disks)
• Databases have two file names
• Logical file name
• Physical file name


Data Integrity
• The Transaction Log
• Automatically created with a database
• Records all activity in a database
• SQL Server uses write-ahead strategy
1. Data pages are loaded into a buffer cache
2. Any updates are made to the copy in the buffer
3. A log record is created in a log cache
4. Checkpoint process saves the log record to disk
• Only then is the data saved to disk


Recovery Models
• Simple
• Log is truncated at checkpoint
• Recovery to the point of the last full or differential backup
• Full
• All operations are fully logged
• Recovery to any point in time
• Bulk-logged
• Faster bulk-logged operations (indexing, bulk load)
• Recovery limited to logged transactions after the last
backup


Creating Databases
• Use Management Studio or Transact-SQL
• SSMS uses T-SQL behind the scenes
• Almost all SSMS actions follow this pattern
• Most of the time you can access that code


Rules for SQL Server Identifiers
• All object names must meet these requirements
• Length: 1 – 128 characters
• First character: letter, @, #, _ (no numbers)
• @ only for local variables and parameters in T-SQL
• # only for local temporary objects (temp tables)
• ## for global temporary tables (span connections)
• Additional characters: letters, numbers, #, $, _
• Use square brackets or double quotes if identifier has
spaces or other special characters
• No use of reserved keywords as identifiers


Modifying Database Options
• Once you create the database, can set
additional options


Creating Tables
• New database doesn’t contain tables
• Table names must be unique
• General format:
server.database.schema_name.object_name
• Usually can simplify
schema_name.object_name
• Most work is creating the columns
• Can also define constraints


Schemas
• Before SQL Server 2005, schema names based
on user names
• Except for dbo
• Close tie was inconvenient
• Now conforms to SQL standard
• Use any valid identifier for schema names
• Can assign same schema to multiple users
• Assign permissions to schema


SQL Server Data Types
• Character-based data types
• Non-Unicode
• char — fixed length, up to 8,000
• varchar — variable length, can set max
• text — long values, up to 2 billion bytes
• varchar(max) — long values, up to 2 billion bytes
• Unicode equivalents
• nchar — fixed length, up to 4,000
• nvarchar — variable length, can set max
• ntext — long Unicode values
• nvarchar(max) — long Unicode values


• Numeric data types
• Whole Numbers
• bit — 1 or 0, one bit of storage
• tinyint — 0 to 255, one byte
• smallint — +/- 32 K, two bytes
• int — +/- 2 billion, four bytes
• bigint — +/- 9 quintillion, 8 bytes


• Fractional Numbers
• real — floating point, 4 bytes
• float — floating point, 8 bytes
• decimal/numeric — scaled integer
storage varies (5 to 17 bytes)
precision: total number of digits
(maximum of 38)
scale: digits to the right of decimal
each combination is a different type


• Fractional Numbers
• money — scaled integer, 8 bytes
+/- 900 trillion
4 digits to the right of the decimal
• smallmoney — scaled integer, 4 bytes
+/- 200 thousand
4 digits to the right of the decimal


• Date data types
• datetime — 8 bytes
4 bytes: days before or after 1/1/1900
(range: 1/1/1753-12/31/9999)
4 bytes: milliseconds after midnight
(rounded to .000, .003, .007 sec.)
• smalldatetime — 4 bytes
2 bytes: days after 1/1/1900
(range: 1/1/1900-6/6/2079)
2 bytes: minutes after midnight


• Date data types
• date — 3 bytes
• Range: 0001-01-01 to 9999-12-31
• time — 3 to 5 bytes
• Range: 00:00:00.0000000 to 23:59:59.9999999
• Precision up to 100 nanoseconds
• datetime2 — 6 to 8 bytes
• Range and precision of date and time types
• No time zone or daylight savings time information
• datetimeoffset — 8 to 10 bytes
• datetime2 with time zone information
• YYYY-MM-DDThh:mm:ss[.nnnnnnn][{+|-}hh:mm]
• YYYY-MM-DDThh:mm:ss[.nnnnnnn]Z


• Binary data types
• binary — up to 8000 bytes, fixed length
• varbinary — variable length
• image — long values, up to 2 billion bytes
• varbinary(max) — long values, up to 2 billion bytes


• Identifier data types
• The identity property
• Not really a separate data type
• Can be set for: tinyint, smallint, int, bigint, decimal, or
numeric
• Configure seed and increment values


• Identifier data types
• uniqueidentifier — a 16-byte GUID
{40700425-0080-11d2-851f-00c04fc21759}
• Used by SQL Server for replication
• newid() function as default generates random IDs
• newsequentialid() better for indexing
• timestamp/rowversion — 8-byte unique binary
• Updated automatically when row is modified
• Unrelated to time
• Used to track data changes (compare old and current values to see
if row has changed)


• The sql_variant data type
• Introduced in SQL Server 2000
• Can hold any other type of value,
except text, ntext, image, *(max), xml, and
timestamp
• Useful for name/value pairs where the data type
for the values may vary
• More overhead than any other data types
• Stores meta data as well as data:base data type,
maximum size, scale, precision, and collation


• Variable-only data types (not used in tables)
• table
• Temporary storage of a result set
• Local scope
• Used like any table, e.g., in FROM clause
• No indexing or transactions
• Primarily used for results from table-valued user-defined
functions
• Cursor
• Used for variables or output parameters
• Reference to a cursor


• xml data type
• Up to 2 Gigabytes
• Available for table columns or for variables
• Can reference an XML schema collection (typed
xml)
• Special methods for querying and modifying xml
• Special indexes store individual xml nodes and
paths to the nodes from the root
• T-SQL supports a subset of the emerging XQuery
standard for querying xml data


• System SQLCLR types
• Geometry and Geography for spatial data
• HierarchyID for hierarchical data


• User-Defined Types
• Composed of standard types with saved settings
• Or based on .NET assemblies


Computed Columns
• Let you create a column that automatically
updates values
• Based on expression that you define
• Can include references to other columns


Creating Constraints
• Can restrict data that users enter in columns
• Set restrictions, or constraints
• Can place on columns as part of creating tables
• Or add them later

• Types
• Primary key
• Foreign key
• Not Null
• Default
• Check
• Unique


Default Constraints
• Enables a value to be entered automatically
into a new row
• When no other data is explicitly entered in that
column
• Define one default constraint per column


Check Constraints
• Checks the data before saving record
• If incoming data violates constraint, record isn’t
saved
• If value of constraint expression is False, constraint
is violated
• If null, will save data


Triggers
• Available on INSERT, UPDATE, DELETE
• Access to special views: deleted, inserted
• Can access and alter values in other tables
• Uses:
• Business rules, Audit trails, roll back
• Originally used for referential integrity
• Caution: Maintenance and perf headaches
• Instead, use stored procedures for data modification
if possible


Creating Indexes
• Indexes let users query data efficiently
• SQL Server can use a shortcut to find data
• Instead of scanning entire table


Using Database Diagrams
• Uses
• Define foreign key constrains
• Get high-level structure view of database
• Perform other design tasks


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Designing and Creating an SQL Server Database

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