SQL Integrity Constraints 1

8/8/2019 SQL Integrity Constraints 1

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STRUCTURED QUERY

LANGUAGE (SQL)


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STRUCTURED QUERY LANGUAGE SQL stands for Structured Query Language and can be

pronounced as SQL or sequel (Structured English QueryLanguage).

It is a query language used for accessing and modifyinginformation in the database.

IBM first developed SQL in 1970s. Also it is an ANSI/ISOstandard.It has become a Standard Universal Language usedby most of the relational database management systems(RDBMS).

Some of the RDBMS systems are: Oracle, Microsoft SQLserver, Sybase etc.Most of these have provided their own

implementation thus enhancing it's feature and making it apowerful tool.

Few of the sql commands used in sql programming areSELECT Statement, UPDATE Statement, INSERT INTOStatement, DELETE Statement, WHERE Clause, ORDER

BY Clause, GROUP BY Clause, ORDER Clause, Joins,Views, GROUP Functions, Indexes etc.


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CREATE DATABASE Statement The CREATE DATABASE statement is used

to create a database.

SQL CREATE DATABASE Syntax

CREATE DATABASE database_name


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The CREATE TABLE Statement The CREATE TABLE statement is used to create a

table in a database.

SQL CREATE TAB

LE Syntax CREATE TABLE table_name

(column_name1 data_type,column_name2 data_type,column_name3 data_type,....

)


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STRUCTURED QUERY LANGUAGE In a simple manner, SQL is a non-procedural,

English-like language that processes data in groupsof records rather than one record at a time.Fewfunctions of SQL are:

store data

modify data

retrieve data modify data

delete data

create tables and other database objects


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STRUCTURED QUERY LANGUAGE Database Tables

A database most often contains one or more tables. Each table isidentified by a name (e.g. "Customers" or "Orders"). Tables containrecords (rows) with data.

Below is an example of a table called "Persons":

P_Id LastName FirstName Address City

1 HANSEN ANNIE L.A CAL

2 PEETERSON R ICKY N.Y N.Y

3 SLEDON JONES GER CHI


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STRUCTURED QUERY LANGUAGE SQL Statements

Most of the actions you need to perform on a

database are done with SQL statements.

The following SQL statement will select all

the records in the "Persons" table:

SELECT * FROM Persons


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SQL DML and DDL SQL can be divided into two parts: The Data Manipulation Language (DML) and

the Data Definition Language (DDL).

The query and update commands form the DML part of SQL:

SELECT - extracts data from a database

UPDATE - updates data in a database DELETE - deletes data from a database

INSERT INTO - inserts new data into a database

The DDL part of SQL permits database tables to be created or deleted.It alsodefine indexes (keys), specify links between tables, and impose constraintsbetween tables. The most important DDL statements in SQL are:

CREATE DATABASE - creates a new database

ALTER DATABASE - modifies a database CREATE TABLE - creates a new table

ALTER TABLE - modifies a table

DROP TABLE - deletes a table

CREATE INDEX - creates an index (search key)

DROPINDEX - deletes an index


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SQL SELECT Statement The SELECT statement is used to select data from a

database.

The result is stored in a result table, called the result-set.

SQL SELECT Syntax

SELECT column_name(s)F

ROM

table_name and

SELECT * FROM table_name


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SQL SELECT DISTINCT Statement In a table, some of the columns may contain

duplicate values. This is not a problem, however,

sometimes you will want to list only the different(distinct) values in a table.

The DISTINCT keyword can be used to return only

distinct (different) values.

SQL SELECT DISTINCT Syntax

SELECT DISTINCT column_name(s)

FROM table_name


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WHERE Clause The WHERE clause is used to extract only

those records that fulfill a specified criterion.

SQL WHERE Syntax

SELECT column_name(s)

FROM table_name

WHERE column_name operator value


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ORDERBY Keyword The ORDERBY keyword is used to sort the result-

set by a specified column.

The ORDERBY keyword sort the records inascending order by default.

If you want to sort the records in a descending order,you can use the DESC keyword.

SQL ORDERB

Y Syntax SELECT column_name(s)

FROM table_nameORDERBY column_name(s) ASC|DESC


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INSERT INTO Statement The INSERT INTO statement is used to insert a new row in a

table.

SQL INSERT INTO Syntax

It is possible to write the INSERT INTO statement in twoforms.

The first form doesn't specify the column names where thedata will be inserted, only their values:

INSERT INTO table_nameVALUES (value1, value2, value3,...)

The second form specifies both the column names and thevalues to be inserted:

INSERT INTO table_name (column1, column2, column3,...)VALUES (value1, value2, value3,...)


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UPDATE Statement The UPDATE statement is used to update

existing records in a table.

SQL UPDATE Syntax

UPDATE table_name

SET column1=value, column2=value2,...

WHERE some_column=some_value


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DELETE Statement The DELETE statement is used to delete rows

in a table.

SQL DELETE Syntax

DELETE FROM table_name

WHERE some_column=some_value


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SQL Wildcards SQL wildcards can substitute for one or more

characters when searching for data in a database.

SQL wildcards must be used with the SQL LIKE

operator WildcardDescription

% ->A substitute for zero or more characters

_ A substitute for exactly one character

[charlist] ->Any single character in charlist [^charlist] or [!charlist] ->Any single character not

in charlist


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IN Operator The IN operator allows you to specify

multiple values in a WHERE clause.

SQL IN Syntax


FROM table_name

WHERE column_name IN (value1,value2,...)


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BETWEEN Operator The BETWEEN operator selects a range of

data between two values. The values can be

numbers, text, or dates. SQL BETWEEN Syntax


FROM table_nameWHERE column_name BETWEEN value1

AND value2


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SQL Alias You can give a table or a column another name by using an

alias. This can be a good thing to do if you have very long orcomplex table names or column names.

An alias name could be anything, but usually it is short. SQL Alias Syntax for Tables

SELECT column_name(s)FROM table_nameAS alias_nameSQL Alias Syntax for Columns

SELECT column_name AS alias_nameFROM table_name


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SQL JOIN The JOIN keyword is used in an SQL statement to

query data from two or more tables, based on arelationship between certain columns in these tables.

Tables in a database are often related to each otherwith keys.

A primary key is a column (or a combination ofcolumns) with a unique value for each row. Each

primary key value must be unique within the table.The purpose is to bind data together, across tables,without repeating all of the data in every table.


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Different SQL JOINs JOIN: Return rows when there is at least one match

in both tables

LEFT JOIN: Return all rows from the left table,even if there are no matches in the right table

RIGHT JOIN: Return all rows from the right table,

even if there are no matches in the left table

FULL JOIN: Return rows when there is a match inone of the tables


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SQL INNER JOIN Keyword The INNER JOIN keyword return rows when

there is at least one match in both tables.

SQL INNER JOIN Syntax SELECT column_name (s)

FROM table_name1INNER JOIN table_name2

ONtable_name1.column_name=table_name2.column_nameok


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SQL LEFT JOIN Keyword The LEFT JOIN keyword returns all rows from the

left table (table_name1), even if there are no matchesin the right table (table_name2).

SQL LEFT JOIN Syntax

SELECT column_name(s)FROM table_name1LEFT JOIN table_name2

ONtable_name1.column_name=table_name2.column_name


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SQL RIGHT JOIN Keyword The RIGHT JOIN keyword Return all rows from the

right table (table_name2), even if there are nomatches in the left table (table_name1).

SQL RIGHT JOIN Syntax

SELECT column_name(s)FROM table_name1RIGHT JOIN table_name2



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SQL FULL JOIN Keyword The FULL JOIN keyword return rows when

there is a match in one of the tables.

SQL FULL JOIN Syntax SELECT column_name(s)

FROM table_name1FULL JOIN table_name2



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SQL UNION Operator The UNION operator is used to combine the result-

set of two or more SELECT statements.

Notice that each SELECT statement within the

UNION must have the same number of columns.The columns must also have similar data types. Also,the columns in each SELECT statement must be inthe same order.

SQL UNION Syntax

SELECT column_name(s) FROM table_name1UNIONSELECT column_name(s) FROM table_name2


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SQL Dates Different Functions of SQL dates

NOW() -Returns the current date and time

CURDATE() -Returns the current date

CURTIME() -Returns the current time

DATE() -Extracts the date part of a date or date/time expression EXTRACT() -Returns a single part of a date/time

DATE_ADD() -Adds a specified time interval to a date

DATE_SUB() -Subtracts a specified time interval from a date

DATEDIFF() -Returns the number of days between two dates

DATE_FORMAT() -Displays date/time data in different formats


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SQL Server Date Functions Function

GETDATE() -Returns the current date and time

DATEPART() -Returns a single part of a date/time DATEADD() -Adds or subtracts a specified time

interval from a date

DATEDIFF() -Returns the time between two dates

CONVERT() -Displays date/time data in different

formats


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SQL Date Data Types MySQL comes with the following data types for storing a date or a

date/time value in the database:

DATE - format YYYY-MM-DD

DATETIME - format: YYYY-MM-DD HH:MM:SS

TIMESTAMP - format: YYYY-MM-DD HH:MM:SS YEAR- format YYYY or YY

SQL Server comes with the following data types for storing a date or adate/time value in the database:

DATE - format YYYY-MM-DD

DATETIME - format: YYYY-MM-DD HH:MM:SS SMALLDATETIME - format: YYYY-MM-DD HH:MM:SS

TIMESTAMP - format: a unique number


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SQL Aggregate Functions SQL aggregate functions return a single value,

calculated from values in a column.

Useful aggregate functions:

AVG() - Returns the average value COUNT() - Returns the number of rows

FIRST() - Returns the first value

LAST() - Returns the last value

MAX() - Returns the largest value MIN() - Returns the smallest value

SUM() - Returns the sum


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SQL Scalar functions SQL scalar functions return a single value, based on the input

value.

Useful scalar functions:

UCASE() - Converts a field to upper case LCASE() - Converts a field to lower case

MID() - Extract characters from a text field

LEN() - Returns the length of a text field

ROUND() - Rounds a numeric field to the number of decimalsspecified

NOW() - Returns the current system date and time

FORMAT() - Formats how a field is to be displayed


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AVG() Function The AVG() function returns the average value

of a numeric column.

SQL AVG() Syntax

SELECT AVG(column_name) FROM

table_name


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COUNT() function The COUNT() function returns the number of rows that matches a

specified criteria.

SQL COUNT(column_name) Syntax

The COUNT(column_name) function returns the number of values

(NULL values will not be counted) of the specified column: SELECT COUNT(column_name) FROM table_nameSQL COUNT(*)

Syntax

The COUNT(*) function returns the number of records in a table:

SELECT COUNT(*) FROM table_name

SQL COUNT(DISTINCT column_name) Syntax

The COUNT(DISTINCT column_name) function returns the number ofdistinct values of the specified column:

SELECT COUNT(DISTINCT column_name) FROM table_name


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FIRST() Function The FIRST() function returns the first value of

the selected column.

SQL FIRST() Syntax

SELECT FIRST(column_name) FROM

table_name


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LAST() Function The LAST() function returns the last value of

the selected column.

SQL LAST() Syntax

SELECT LAST(column_name) FROM

table_name


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MIN() Function The MIN() function returns the smallest value

of the selected column.

SQL MIN() Syntax

SELECT MIN(column_name) FROM

table_name


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SUM() Function The SUM() function returns the total sum of a

numeric column.

SQL SUM() Syntax

SELECT SUM(column_name) FROM

table_name


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GROUP BY Statement The GROUP BY statement is used in

conjunction with the aggregate functions to

group the result-set by one or more columns.

SQL GROUP BY Syntax

SELECT column_name,aggregate_function(column_name)

FROM table_nameWHERE column_name operator valueGROUP BY column_name


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HAVING Clause The HAVING clause was added to SQL because the

WHERE keyword could not be used with aggregatefunctions.

SQL HAVING Syntax SELECT column_name,

aggregate_function(column_name)FROM table_nameWHERE column_name operator value

GROUP BY column_nameHAVING aggregate_function(column_name)operator value


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UCASE() Function The UCASE() function converts the value of a

field to uppercase.

SQL UCASE() Syntax

SELECT UCASE(column_name) FROM

table_nameSyntax for SQL Server

SELECT UPPER(column_name) FROMtable_name


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LCASE() Function The LCASE() function converts the value of a

field to lowercase.

SQL LCASE() Syntax

SELECT LCASE(column_name) FROM

table_nameSyntax for SQL Server

SELECT LOWER(column_name) FROMtable_name


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MID() Function The MID() function is used to extract characters from a text

field.

SQL MID() Syntax

SELECT MID(column_name,start[,length]) FROM table_name column_name -> Required. The field to extract characters from

Start -> Required. Specifies the starting position (starts at 1)

Length -> Optional. The number of characters to return.If

omitted, theMI

D() function returns the rest of the text


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LEN() Function The LEN() function returns the length of the

value in a text field.

SQL LEN() Syntax SELECT LEN(column_name) FROM

table_name


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ROUND() Function The ROUND() Function

The ROUND() function is used to round a numericfield to the number of decimals specified.

SQL ROUND() Syntax

SELECT ROUND(column_name,decimals) FROMtable_name

column_name -> Required.The field to round

.

Decimals -> Required. Specifies the number ofdecimals to be returned.


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NOW() Function The NOW() function returns the current

system date and time.

SQL NOW() Syntax SELECT NOW() FROM table_name


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FORMAT() Function The FORMAT() function is used to format how

a field is to be displayed.

SQL FORMAT() Syntax SELECT FORMAT(column_name,format)

FROM table_name

column_name -> Required. The field to beformatted.

Format -> Required. Specifies the format


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SQL Integrity ConstraintsIntegrity Constraints are used to apply business rulesfor the database tables.

The constraints available in SQL are Foreign Key,Not Null, Unique, Check.Constraints can be defined in two ways1) The constraints can be specified immediately afterthe column definition. This is called column-leveldefinition.2) The constraints can be specified after all the columnsare defined. This is called table-level definition.


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SQL Primary key This constraint defines a column or combination of

columns which uniquely identifies each row in the

table.

Syntax to define a Primary key at column level:

column name datatype [CONSTRAINT

constraint_name] PRIMARY KEY

Syntax to define a Primary key at table level:

[CONSTRAINT constraint_name] PRIMARY KEY

(column_name1,column_name2,..)


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SQL Primary key For Example: To create an employee table with Primary Key constraint, the

query would be like.

Primary Key at table level: CREATE TABLE employee

( id number(5) PRIMARY KEY,

name char(20),dept char(10),age number(2),salary number(10),location char(10));

or

CREATE TABLE employee( id number(5) CONSTRAINT emp_id_pkPRIMARY KEY,name char(20),dept char(10),age number(2),salary number(10),location char(10));


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SQL Primary key

Primary Key at table level:

CREATE TABLE employee

( id number(5),

name char(20),

dept char(10),

age number(2),

salary number(10),

location char(10),

CONSTRAINT emp_id_pkPRIMARY KEY (id));


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SQL Foreign key or Referential Integrity This constraint identifies any column referencing the PRIMARY

KEY in another table. It establishes a relationship between twocolumns in the same table or between different tables. For a columnto be defined as a Foreign Key, it should be a defined as a PrimaryKey in the table which it is referring. One or more columns can be

defined as Foreign key.

Syntax to define a Foreign key at column level:

[CONSTRAINT constraint_name] REFERENCESReferenced_Table_name(column_name)

Syntax to define a Foreign key at table level:

[CONSTRAINT constraint_name] FOREIGN KEY(column_name)REFERENCES referenced_table_name(column_name);


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SQL Foreign key or Referential Integrity For Example:

1) Lets use the "product" table and "order_items".

Foreign Key at column level:

CREATE TABLE product( product_id number(5) CONSTRAINT pd_id_pkPRIMARY KEY,

product_name char(20),supplier_name char(20),unit_price number(10));

CREATE TABLE order_items( order_id number(5) CONSTRAINT od_id_pkPRIMARY KEY,product_id number(5) CONSTRAINT pd_id_fk REFERENCES, product(product_id),

product_name char(20),supplier_name char(20),unit_price number(10));


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SQLF

oreign key or ReferentialIntegrity

Foreign Key at table level:

CREATE TABLE order_items( order_id number(5) ,product_id number(5),product_name char(20),supplier_name char(20),unit_price number(10)CONSTRAINT od_id_pkPRIMARY KEY(order_id),CONSTRAINT pd_id_fk FOREIGN KEY(product_id) REFERENCESproduct(product_id));2) If the employee table has a 'mgr_id' i.e, manager id as a foreign key whichreferences primary key 'id' within the same table, the query would be like,

CREATE TABLE employee( id number(5) PRIMARY KEY,name char(20),dept char(10),age number(2),mgr_id number(5) REFERENCES employee(id),salary number(10),location char(10)

);


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SQL Not Null Constraint This constraint ensures all rows in the table

contain a definite value for the column which

is specified as not null. Which means a nullvalue is not allowed.

Syntax to define a Not Null constraint:

[CONSTRAINT constraint name] NOTNULL


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SQL Not Null Constraint For Example: To create a employee table with Null value,

the query would be like

CREATE TABLE employee( id number(5),name char(20) CONSTRAINT nm_nn NOT NULL,dept char(10),age number(2),

salary number(10),location char(10));


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SQL Unique Key This constraint ensures that a column or a group of

columns in each row have a distinct value. A

column(s) can have a null value but the values

cannot be duplicated.

Syntax to define a Unique key at column level:

[CONSTRAINT constraint_name] UNIQUE

Syntax to define a Unique key at table level:

[CONSTRAINT constraint_name]

UNIQUE(column_name)


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SQL Unique Key For Example: To create an employee table with Unique key, the query would be

like,

Unique Key at column level:

CREATE TABLE employee( id number(5) PRIMARY KEY,

name char(20),dept char(10),age number(2),salary number(10),location char(10) UNIQUE);

or

CREATE TABLE employee( id number(5) PRIMARY KEY,name char(20),dept char(10),age number(2),salary number(10),location char(10) CONSTRAINT loc_un UNIQUE

);


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SQL Unique Key Unique Key at table level:


name char(20),dept char(10),age number(2),salary number(10),location char(10),

CONSTRAINT loc_un UNIQUE(location));


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SQL Check Constraint This constraint defines a business rule on a column.

All the rows must satisfy this rule. The constraint

can be applied for a single column or a group of

columns.

Syntax to define a Check constraint:

[CONSTRAINT constraint_name] CHECK

(condition) For Example: In the employee table to select the

gender of a person, the query would be like


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SQL Check Constraint Check Constraint at column level:

CREATE TABLE employee( id number(5) PRIMARY KEY,name char(20),dept char(10),age number(2),

gender char(1) CHECK (gender in ('M','F')),salary number(10),location char(10));

Check Constraint at table level:


name char(20),dept char(10),age number(2),gender char(1),salary number(10),location char(10),CONSTRAINT gender_ck CHECK (gender in ('M','F')));


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SQL DEF

AULT Constraint The DEFAULT constraint is used to insert a

default value into a column.

The default value will be added to all newrecords, if no other value is specified.


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SQL Integrity Constraints 1

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