intro to tsql unit 7
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Introduction To SQLUnit 7
Modern Business Technology
Introduction To TSQLUnit 7
Developed by
Michael Hotek
Integrity
• Integrity is the process by which data is validated and consistency is enforced
• Databases were designed with integrity as a primary factor
• Integrity can be enforced by a variety of means– Rules– Defaults– Constraints– Primary keys– Foreign keys– Unique indexes– Triggers
• Integrity can also be programmatic or declarative
Declarative Integrity
• Defaults and constraints can be used directly in a create table statement, hence declarative integrity
• Constraints include– Check– Unique– Primary Key– Reference
• Constraints can be column or table level
• Defaults are only column level
Defaults
• A default clause is used to supply a value for a column when one is not explicitly specified in an insert statement
• For a DEFAULT constraint:[CONSTRAINT constraint_name]
DEFAULT {constant_expression | niladic-function | NULL}
[FOR col_name]
create table address
(CompID int not null,
Address varchar(50) not null,
City varchar(30)
default 'Chicago',
State char(2) default 'IL')
Defaults
• Functions can also be used in place of constants as long as they return a single value
• The value of the default must match the datatype of the column
• Character and date values must be enclosed in quotes
• A column can have only one default• sp_helpconstraint can be used to
return constraint information about a table.
Check Constraints
• Check constraints are used to enforce domain integrity
• Can be applied at a table and a column level
• Constraints are used to specify:– List or set of values– range of values– Format for data– Conditions on a value
• Enforced during inserts and updates• Must evaluate to a true or false
Column Constraints
create table people
(SSN char(11) not null
constraint chk_ssn
check (SSN like '[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]',
FirstName varchar(30) not null,
LastNamevarchar(50) not null,
…)
orcreate table people
(SSN char(11) not null
check (SSN like '[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]',
FirstName varchar(30) not null,
LastNamevarchar(50) not null,
…)
Table Constraints
• Used for more than one columncreate table discounts
(Type varchar(40) not null,
StoreID char(4) not null,
LowQty int not null,
HighQty int not null,
Discountfloat null,
constraint chk_low_high
check (LowQty <= HighQty))
Indexes
• Separate structure attached to a table
• Contain pointers to the physical data• Used to increase performance when:
– Finding rows– Correlating data across tables– Ordering result sets– Inserting data in some cases
• Can enforce unique values in a column or table
CREATE [UNIQUE] [CLUSTERED | NONCLUSTERED] INDEX index_name
ON [[database.]owner.]table_name (column_name [, column_name]...)[WITH[FILLFACTOR = x][[,] IGNORE_DUP_KEY]
[[,] {SORTED_DATA |SORTED_DATA_REORG}]
[[,] {IGNORE_DUP_ROW |ALLOW_DUP_ROW}]][ON segment_name]
Pages
• Data is stored in SQL Server is a set of structures called pages
• Each page is 2K in size (8K in 7.0)• Many rows can be on a single page• A single row must be contained
entirely on a page• Each page contains a header area
that identifies the contents of each page
• Pages are stored in a doubly linked list
Indexes
• As data gets added, a large number of pages are created
• Indexes were devised to quickly navigate these pages
• Indexes are also stored in pages • The index pages are stored in a B-
Tree to support quick location of information
177-32-1176
756-30-7391
756-30-7391
899-46-2035
177-32-1176
267-41-2394
409-56-7008
177-32-1176...
213-46-8915...
238-95-7766...
267-41-2394...
341-53-8472...
402-31-7808...
409-56-7008...
532-86-9471...
655-27-5281...
756-30-7391...
775-93-6481...
835-21-6639...
Data PagesIndex Pages
Indexes
Indexes
• There are two types of indexes– clustered– nonclusterd
• Only be 1 clustered index per table• Up to 249 nonclustered indexes• Order of data in the table is
determined by the type of index– clustered index
• Data in the same order as the index
– nonclustered index• Data in the order it was inserted
Keys and Indexes
• Keys:• Logical
– Primary, foreign, and common
• Physical– Single column or composite– This is an index
• Indexes are not necessarily logical keys
• Indexes can be applied to columns that are not keys
• Can contain up to 16 columns• Can have a maximum size of 256
bytes
Clustered Index
• Only one per table• This is your most powerful index• Physically orders the data in a table• Can be equated to the old card
catalog• Good for range searches• Slow for inserts
– page splitting
Clustered Indexes
Bennet 1007Page 1001
Karsen 1009Smith 1062
Key ptr
Karsen 1315Page 1009Key ptr
Bennet 1132Page 1007
Greane 1133Hunter 1127
Key ptr
HunterPage 11127
Jenkins
GreanePage 1133
GreenGreene
BennetPage 1132
Chan
EdwardsDull
Data Pages
Leaf LevelIntermediateRoot Page
Clustered Indexes
• The leaf level of the index is the data page of the table
• Only one entry can point to a page in the next level
• Require an additional 120% of space during creation
Nonclustered Indexes
• Data is stored in a random order at the data page level
• Up to 249 nonclustered indexes can be defined per table
• Good for searches of explicit values• Are much larger than a clustered
index
Page 1001Bennet 10071421,1Karsen 13051876,1Smith 10621242,1
Page 1007Bennet 11321421,1Greane 11331242,4Hunter 11271242,1
Page 1305Karsen 13111876,1
Page 1133Greane 1242,4Green 1409,2Greene 1421,2
Page 1127Hunter 1242,1Jenkins 1241,4
Page 142118 Bennet19 Greene20 Ringer
Page 140921 Dull22 Green23 White
Page 124110 O'Leary11 Ringer12 White13 Jenkins
Page 124214 Hunter15 Smith16 Ringer17 Greane
Page 1132Bennet 1421,1Chan 1129,3Dull 1409,1
Edwards 1018,5
KeyRowptr
Pageptr
KeyRowptr
Pageptr
KeyRowptr
Root Page Intermediate Leaf Pages Data Pages
Nonclustered Indexes
Nonclustered Indexes
• The root and intermediate levels work similarly for both clustered and nonclustered indexes
• The leaf level of a nonclustered index contains a pointer to the row on each data page
• The pointers at the leaf level are in index order
Unique Constraint
• Ensures no two rows have the same value
• Allows one null value in a column• Creates a unique, nonclustered index
by default
create table publishers
(pub_id char(4) null,
constraint u_pub_id unique,
pub_namevarchar(30) not null)
Primary Key
• Ensures no two rows have the same value
• Nulls are not allowed• Creates a unique, clustered index by
default
create table publishers
(pub_id char(4)
constraint publishers_PK primary key,
pub_namevarchar(30))
create table sales
(stor_idchar(4) not null,
ord_num varchar(20) not null,
date datetime nit null,
constraint sales_PK primary key
nonclustered (stor_id, ord_num))
Referential Integrity
• Used to maintain foreign keys when data is inserted or updated
• Columncreate table <table name>
(column datatype
[constraint constraint_name]
references ref_table [ref_column]
• Table[constraint constraint_name]
foreign key (column [{,column}…])
references ref_table
[(column [{, column}…])]
Referential Integrity
• Use a column level constraint when only one column needs to be compared
• Use a table level constraint when more than one column needs to be compared
• The table in the references clause must already have a primary/unique constraint or a unique index defined on the columns
• A roll back is issued if referential integrity is violated and a message is sent back
Referential Integrity
• Column Levelcreate table titles
(title_id tid not null,
title varchar(80) null,
pub_id char(4) null
constraint publishers_pub_id
references publishers(pub_id),
notes varchar(200) null)
• Restrictions
Referential Integrity
create table salesdetail
(stor_idchar(4) not null,
ord_num varchar(20) not null,
title_idtid not null,
qty int not null,
discountfloat not null,
constraint salesdetail_FK1
foreign key (stor_id, ord_num)
references sales(stor_id, ord_num),
constraint salesdetail_FK2
foreign key (title_id)
references titles(title_id))
Referential Integrity
• When primary keys are deleted and updated, three different option could be performed:– Restrict– Cascade– Set null
• Declarative RI enforces a restrict• Cascade and set null can only be
accomplished with triggers• In a perfect world, updates to a
primary key are not allowed• In an imperfect world, these should
be kept to a minimum
Error Messages
• Custom messages can be added with sp_addmessage
• Drop a message with sp_dropmessage
• Get a message with sp_getmessage• In Sybase, these messages can be
bound to a constraint so that on a failure, a nice message to returned to the user
• Bind messages using sp_bindmsg• Unbind messages using
sp_unbindmsg
Alter Table
• Once a table is created, certain modifications to its structure can be performed
• Allowed:– Add columns– Add, drop, or change constraints
• Not allowed– Dropping columns– Changing datatypes– Changing width of columns– Changing nullability options
• Constraints can only be modified with an alter table statement
• Modifications to constraints do not affect existing data
Alter Table
ALTER TABLE [database.[owner].]table_name [WITH NOCHECK][ADD
{col_name column_properties [column_constraints]
| [[,] table_constraint]}[, {next_col_name |
next_table_constraint}]...]| [DROP [CONSTRAINT]
constraint_name [, constraint_name2]...]
Getting Help
• To obtain information about constraints and defaults defined for a table use
sp_helpconstraint table
Unit 7 Review
• Constraints are used to enforce integrity
• A default will supply a value during an insert
• Check constraints enforce valid data during inserts and updates
• Data is stored in data pages that are 2K in size
• A table can have 1 clustered index
– Physically orders the data
– Leaf level of index is the data pages
– Used for range searches
• A table can have up to 249 nonclusterd indexes
– Does not order the data
– The leaf level of the index contains pointers to rows
– Used for explicit searches
• Indexes can have up to 16 columns
• Can be a maximum of 256 bytes
• Unique constraint creates a unique, nonclustered index by default and allows one null
• Primary key constraint creates a unique, clustered index by default and doe not allow nulls
• Foreign keys are enforced via a references constraint
• Referenced column(s) must have a primary/unique constraint or a unique index defined
• Roll back is performed if RI is violated
• The only type of RI that can be applied when modifying a primary key with constraints is restrict
• You can add custom messages
• Alter table can add columns
• Alter can add, drop, or modify constraints
• You can not drop a column
• You can not change a datatype
• You can not change the length of a column
• You can not change the nullability
Unit 7 Review
• Time allotted for exercises is 30 minutes
Unit 7 Exercises
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