SQL Advanced 2

8/9/2019 SQL Advanced 2

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Experiment No. – 9, 10

(2)Aim: To Study SQL Advn!ed.

T"eory:

SQL Constraints

Constraints are used to limit the type of data that can go into a table.

Constraints can be specified when a table is created (with the CREATE TABLE statement) or after the

table is created (with the ALTER TABLE statement).

e will focus on the following constraints!

• "#T "$LL

•

$"%&$E• 'R%AR *E

• +#RE%," *E

• C-EC*

• E+A$LT

1.SQL NOT NULL Constraint

The "#T "$LL constraint enforces a column to "#T accept "$LL /alues.

The "#T "$LL constraint enforces a field to always contain a /alue. This means that you cannot insert a

new record0 or update a record without adding a /alue to this field.

The following 1&L enforces the 2'3%d2 column and the 2Last"ame2 column to not accept "$LL /alues!

CREATE TABLE B%T

(

'3%d int "#T "$LL0

Last"ame /archar(455) "#T "$LL0

+irst"ame /archar(455)0

Address /archar(455)0City /archar(455)

)

SQL# $%EATE TA&LE '&T

2 (

*+d int NT N-LL,

L/tNme vr!"r(2) NT N-LL,


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ir/tNme vr!"r(2),

Addre// vr!"r(2),

3 $ity vr!"r(2)

4 )

9 5

T67e !reted.

SQL# in/ert into '&T 2 v7ue/(1,88,8/n8,8/in8,8mum6i8)5

in/ert into '&T

E%%% t 7ine 1:

%A;0100: !nnot in/ert N-LL into ( !reted.

2.SQL UNIQUE Constraint

The $"%&$E constraint uni6uely identifies each record in a database table.

The $"%&$E and 'R%AR *E constraints both pro/ide a guarantee for uni6ueness for a column or

set of columns.

A 'R%AR *E constraint automatically has a $"%&$E constraint defined on it.

"ote that you can ha/e many $"%&$E constraints per table0 but only one 'R%AR *E constraint per

table.

Syntx:

CREATE TABLE table3name

(

'3%d int "#T "$LL $"%&$E0




)

SQL# $%EATE TA&LE '&T1

2 (

*+d int NT N-LL -NQ-E,


ir/tNme vr!"r(2),

Addre// vr!"r(2),


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3 $ity vr!"r(2)

4 )

9 5

T67e !reted.

3. SQL PRIMARY KEY Constraint on CREATE TABLE

The following 1&L creates a 'R%AR *E on the 2'3%d2 column when the 2B%T42 table is created!

CREATE TABLE B%T4

(

'3%d int "#T "$LL 'R%AR *E0

Last"ame /archar(455) "#T "$LL0+irst"ame /archar(455)0

Address /archar(455)0

City /archar(455))

4. SQL FOREIN KEY Constraint

A +#RE%," *E in one table points to a 'R%AR *E in another table.

Let7s illustrate the foreign 8ey with an e9ample. Loo8 at the following two tables!

The 2B%T2 table!

*+d L/tNme ir/tNme Addre// $ity

: An/ri 1ana 1a8ina8a mumbai

4 1hai8h 1ira; Andheri mumbai

The 2#rders2 table!

+d rderNo *+d

:


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SQL FOREIN KEY Constraint on CREATE TABLE

The following 1&L creates a +#RE%," *E on the 2'3%d2 column when the 2#rders2 table is created!

CREATE TABLE #rders

(#3%d int "#T "$LL 'R%AR *E0

#rder"o int "#T "$LL0

'3%d int +#RE%," *E RE+ERE"CE1 'ersons('3%d)

)

!.SQL C"ECK Constraint

The C-EC* constraint is used to limit the /alue range that can be placed in a column.

%f you define a C-EC* constraint on a single column it allows only certain /alues for this column.

CREATE TABLE B%T

(

'3%d int "#T "$LL C-EC* ('3%d4)0




)

SQL# $%EATE TA&LE '&T

2 (

*+d int NT N-LL $?E$@ (*+d#2),


ir/tNme vr!"r(2),

Addre// vr!"r(2),

3 $ity vr!"r(2)

4 )

9 5

T67e !reted.

SQL# in/ert into '&T

2 v7ue/(1,8/"i"8,8/n8,8/in8,8mum6i8)5

in/ert into '&T

E%%% t 7ine 1:

%A;02290: !"e! !on/trint (S$TT.SS+$000) vio7ted

#. T$% &ROP TABLE Stat%'%nt


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The R#' TABLE statement is used to delete a table.

R#' TABLE table3name

(.T$% &ROP &ATABASE Stat%'%nt

The R#' ATABA1E statement is used to delete a database.

R#' ATABA1E database3name

). T$% TRUNCATE TABLE Stat%'%nt

hat if we only want to delete the data inside the table0 and not the table itself

Then0 use the TR$"CATE TABLE statement!

TR$"CATE TABLE table3name

*.T$% ALTER TABLE Stat%'%nt

The ALTER TABLE statement is used to add0 delete0 or modify columns in an e9isting table.

SQL ALTER TABLE S+nta,

To add a column in a table0 use the following synta9!

ALTER TABLE table3name

A column3name datatype

To delete a column in a table0 use the following synta9 (notice that some database systems don7t allow

deleting a column)!


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ALTER TABLE table3name

R#' C#L$" column3name

$on!7u/ion: Thus we ha/e successfully implemented 1&L ad/anced 6ueries.

SQL Advanced 2

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