sql queries part1

8/19/2019 SQL Queries Part1

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SQL Tutorial

SQL is a standard language for accessing databases.

Our SQL tutorial will teach you how to use SQL to access and manipulatedata in:

MySQL, SQL Server, ccess, Oracle, Sybase, !"#, and other database

systems.

SQL is a standard language for accessing and manipulating databases.

$ntroduction to SQL

SQL is a standard language for accessing and manipulating databases.

%hat is SQL&

• SQL stands for Structured Query Language

• SQL lets you access and manipulate databases

• SQL is an 'S$ (merican 'ational Standards $nstitute) standard

%hat *an SQL do&

• SQL can e+ecute ueries against a database

• SQL can retrieve data from a database

• SQL can insert records in a database

• SQL can update records in a database

• SQL can delete records from a database

• SQL can create new databases

• SQL can create new tables in a database


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• SQL can create stored procedures in a database

• SQL can create views in a database

• SQL can set permissions on tables, procedures, and views

SQL is a Standard - "T....

lthough SQL is an 'S$ (merican 'ational Standards $nstitute) standard, there are many

different versions of the SQL language.

/owever, to be compliant with the 'S$ standard, they all support at least the ma0or commands

(such as S1L1*T, 2!T1, !1L1T1, $'S13T, %/131) in a similar manner.

Note: Most of the SQL database programs also have their own proprietary e+tensions in addition

to the SQL standard4

sing SQL in 5our %eb Site

To build a web site that shows some data from a database, you will need the following:

• n 3!"MS database program (i.e. MS ccess, SQL Server, MySQL)

• server-side scripting language, li6e 2/2 or S2

• SQL

• /TML 7 *SS

3!"MS

3!"MS stands for 3elational !atabase Management System.

3!"MS is the basis for SQL, and for all modern database systems li6e MS SQL Server, $"M !"#,

Oracle, MySQL, and Microsoft ccess.

The data in 3!"MS is stored in database ob0ects called tables.

table is a collection of related data entries and it consists of columns and rows.

SQL Synta+

!atabase Tables

database most often contains one or more tables. 1ach table is identified by a name (e.g.

8*ustomers8 or 8Orders8). Tables contain records (rows) with data.


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"elow is an e+ample of a table called 82ersons8:

P_Id LastName FirstName Address City

9 /ansen Ola Timoteivn 9 Sandnes

# Svendson Tove "orgvn #; Sandnes

; 2ettersen


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• SELECT - e+tracts 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 !!L part of SQL permits database tables to be created or deleted. $t also define inde+es

(6eys), specify lin6s between tables, and impose constraints between tables. The most important

!!L 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 inde+ (search 6ey)

• DROP INDEX - deletes an inde+

SQL S1L1*T Statement

This chapter will e+plain the S1L1*T and the S1L1*T ? statements.

The SQL S1L1*T Statement

The S1L1*T statement is used to select data from a database.

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

SQL S1L1*T Synta+

SELECT column_name(s)

FROM table_name

and

SELECT * FROM table_name

Note: SQL is not case sensitive. S1L1*T is the same as select.


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n SQL S1L1*T 1+ample

The 82ersons8 table:




; 2ettersen irst'ame8 from the

table above.

%e use the following S1L1*T statement:

SELECT LastName,FirstName FROM Persons

The result-set will loo6 li6e this:

LastName FirstName

/ansen Ola

Svendson Tove

2ettersen


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; 2ettersen


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; 2ettersen


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'ow we want to select only the persons living in the city 8Sandnes8 from the table above.


SELECT * FROM Persons

"#ERE Cit!&'Sannes'





Quotes round Te+t >ields

SQL uses single uotes around te+t values (most database systems will also accept double

uotes).

lthough, numeric values should not be enclosed in uotes.

>or te+t values:

Tis is correct

SELECT * FROM Persons "#ERE FirstName&'To%e'

Tis is +ron

SELECT * FROM Persons "#ERE FirstName&To%e

>or numeric values:

Tis is correct

SELECT * FROM Persons "#ERE -ear&./01

Tis is +ron

SELECT * FROM Persons "#ERE -ear&'./01'


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Operators llowed in the %/131 *lause

%ith the %/131 clause, the following operators can be used:

Operator Descriptio

A 1ual

BC 'ot eual

C @reater than

B Less than

CA @reater than or eual

BA Less than or eual

"1T%11' "etween an inclusive range

L$


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; 2ettersen


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'ow we want to select only the persons with the last name eual to 8Svendson8 '! the first

name eual to 8Tove8 O3 to 8Ola8:


SELECT * FROM Persons "#ERELastName&'S%enson'

2ND (FirstName&'To%e' OR FirstName&'Ola')




SQL O3!13 "5


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; 2ettersen


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SQL $'S13T $'TO Statement

The $'S13T $'TO statement is used to insert new records in a table.

The $'S13T $'TO Statement

The $'S13T $'TO statement is used to insert a new row in a table.

SQL $'S13T $'TO Synta+

$t is possible to write the $'S13T $'TO statement in two forms.

The first form doesnGt specify the column names where the data will be inserted, only their values:

NSERT NTO table_name

52L6ES (%alue., %alue7, %alue8,999)

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

NSERT NTO table_name (column., column7, column8,999)

52L6ES (%alue., %alue7, %alue8,999)

SQL $'S13T $'TO 1+ample

%e have the following 82ersons8 table:




; 2ettersen


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NSERT NTO Persons

52L6ES (:,'Nilsen', ';oan', '3a


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The 2!T1 Statement

The 2!T1 statement is used to update e+isting records in a table.

SQL 2!T1 Synta+

6PD2TE table_name

SET column.&%alue, column7&%alue7,999

"#ERE some_column&some_%alue

Note: 'otice the %/131 clause in the 2!T1 synta+. The %/131 clause specifies which record

or records that should be updated. $f you omit the %/131 clause, all records will be updated4

SQL 2!T1 1+ampleThe 82ersons8 table:




; 2ettersen


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I T0essem Ha6ob 'issestien JK Sandnes

SQL 2!T1 %arning

"e careful when updating records. $f we had omitted the %/131 clause in the e+ample above, li6e

this:

6PD2TE Persons

SET 2ress&'Nissestien 0>', Cit!&'Sannes'

The 82ersons8 table would have loo6ed li6e this:


9 /ansen Ola 'issestien JK Sandnes

# Svendson Tove 'issestien JK Sandnes

; 2ettersen


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SQL !1L1T1 1+ample





; 2ettersen


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SQL TO2 *lause

The TO2 *lause

The TO2 clause is used to specify the number of records to return.

The TO2 clause can be very useful on large tables with thousands of records. 3eturning a large

number of records can impact on performance.

Note: 'ot all database systems support the TO2 clause.

SQL Server Synta+

SELECT TOP number4$ercent column_name(s)

FROM table_name

SQL S1L1*T TO2 1uivalent in MySQL and Oracle

MySQL Synta+


FROM table_name

LMT number

1+ample

SELECT *

FROM Persons

LMT 1

Oracle Synta+


FROM table_name

"#ERE RO"N6M ?& number

1+ample

SELECT *

FROM Persons

"#ERE RO"N6M ?&1


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SQL TO2 1+ample





; 2ettersen


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SQL L$


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"#ERE Cit! LAE 'sB'

The 88 sign can be used to define wildcards (missing letters in the pattern) both before and after

the pattern.





; 2ettersen


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SQL %ildcards

SQL wildcards can be used when searching for data in a database.

SQL %ildcards

SQL wildcards can substitute for one or more characters when searching for data in a database.

SQL wildcards must be used with the SQL L$


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; 2ettersen


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"#ERE FirstName LAE '_la'




'e+t, we want to select the persons with a last name that starts with 8S8, followed by any

character, followed by 8end8, followed by any character, followed by 8on8 from the 82ersons8 table.



"#ERE LastName LAE 'S_en_on'




sing the Ncharlist %ildcard

'ow we want to select the persons with a last name that starts with 8b8 or 8s8 or 8p8 from the

82ersons8 table.



"#ERE LastName LAE 'bs$B'




; 2ettersen


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"#ERE LastName LAE 'bs$B'




SQL $' Operator

The $' Operator

The $' operator allows you to specify multiple values in a %/131 clause.

SQL $' Synta+


FROM table_name

"#ERE column_name N (%alue.,%alue7,999)

$' Operator 1+ample





; 2ettersen


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; 2ettersen


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Note: The "1T%11' operator is treated differently in different databases4

$n some databases, persons with the Last'ame of 8/ansen8 or 82ettersen8 will not be listed,

because the "1T%11' operator only selects fields that are between and e+cluding the test values.

$n other databases, persons with the Last'ame of 8/ansen8 or 82ettersen8 will be listed, because

the "1T%11' operator selects fields that are between and including the test values.

nd in other databases, persons with the Last'ame of 8/ansen8 will be listed, but 82ettersen8 will

not be listed (li6e the e+ample above), because the "1T%11' operator selects fields between the

test values, including the first test value and e+cluding the last test value.

Therefore: *hec6 how your database treats the "1T%11' operator.

1+ample #

To display the persons outside the range in the previous e+ample, use 'OT "1T%11':


"#ERE LastName

NOT 3ET"EEN '#ansen' 2ND 'Pettersen'




; 2ettersen


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SQL lias

5ou 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 or comple+ table names or column names.

n alias name could be anything, but usually it is short.

SQL lias Synta+ for Tables


FROM table_name

2S alias_name

SQL lias Synta+ for *olumns

SELECT column_name 2S alias_name

FROM table_name

lias 1+ample

ssume we have a table called 82ersons8 and another table called 82roduct=Orders8. %e will give

the table aliases of 8p8 and 8po8 respectively.

'ow we want to list all the orders that 8Ola /ansen8 is responsible for.


SELECT $o9OrerD, $9LastName, $9FirstName

FROM Persons 2S $,

Prouct_Orers 2S $o

"#ERE $9LastName&'#ansen' 2ND $9FirstName&'Ola'

The same S1L1*T statement without aliases:

SELECT Prouct_Orers9OrerD, Persons9LastName, Persons9FirstName

FROM Persons,

Prouct_Orers

"#ERE Persons9LastName&'#ansen' 2ND Persons9FirstName&'Ola'

s youGll see from the two S1L1*T statements above aliases can ma6e ueries easier to both

write and to read.

SQL Hoins

SQL 0oins are used to uery data from two or more tables, based on a relationshipbetween certain columns in these tables.


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SQL HO$'

The HO$' 6eyword is used in an SQL statement to uery data from two or more tables, based on a

relationship between certain columns in these tables.

Tables in a database are often related to each other with 6eys.

primary 6ey is a column (or a combination of columns) with a uniue value for each row. 1ach

primary 6ey value must be uniue within the table. The purpose is to bind data together, across

tables, without repeating all of the data in every table.

Loo6 at the 82ersons8 table:




; 2ettersen


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• #OIN: 3eturn rows when there is at least one match in both tables

• LEFT #OIN: 3eturn all rows from the left table, even if there are no matches in the right

table

• RI$%T #OIN: 3eturn all rows from the right table, even if there are no matches in the left

table

• FULL #OIN: 3eturn rows when there is a match in one of the tables

SQL $''13 HO$'


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I ;EKJE 9I

'ow we want to list all the persons with any orders.


SELECT Persons9LastName, Persons9FirstName, Orers9OrerNo

FROM Persons

NNER ;ON Orers

ON Persons9P_&Orers9P_

ORDER 3- Persons9LastName


LastName FirstName OrderNo

/ansen Ola ##EIJ

/ansen Ola #EIJ#

2ettersen T HO$' T HO$' T HO$' 6eyword returns all rows from the left table (table=name9), even if there are no

matches in the right table (table=name#).

SQL L1>T HO$' Synta+SELECT column_name(s)

FROM table_name.

LEFT ;ON table_name7

ON table_name.9column_name&table_name79column_name

PS: $n some databases L1>T HO$' is called L1>T OT13 HO$'.

SQL L1>T HO$' 1+ample



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; 2ettersen


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SQL 3$@/T HO$'


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/ansen Ola ##EIJ

/ansen Ola #EIJ#

2ettersen LL HO$' Synta+


FROM table_name.

F6LL ;ON table_name7

ON table_name.9column_name&table_name79column_name

SQL >LL HO$' 1+ample





; 2ettersen


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; ##EIJ 9

E #EIJ# 9

I ;EKJE 9I

'ow we want to list all the persons and their orders, and all the orders with their persons.


SELECT Persons9LastName, Persons9FirstName, Orers9OrerNo

FROM Persons

F6LL ;ON Orers

ON Persons9P_&Orers9P_

ORDER 3- Persons9LastName



/ansen Ola ##EIJ

/ansen Ola #EIJ#

2ettersen


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'otice that each S1L1*T statement within the '$O' must have the same number of columns.

The columns must also have similar data types. lso, the columns in each S1L1*T statement must

be in the same order.

SQL '$O' Synta+

SELECT column_name(s) FROM table_name.6NON

SELECT column_name(s) FROM table_name7

Note: The '$O' operator selects only distinct values by default. To allow duplicate values, use

'$O' LL.

SQL '$O' LL Synta+

SELECT column_name(s) FROM table_name.

6NON 2LL

SELECT column_name(s) FROM table_name7

PS: The column names in the result-set of a '$O' are always eual to the column names in the

first S1L1*T statement in the '$O'.

SQL '$O' 1+ample

Loo6 at the following tables:

&Emp"oyees_Nor'ay&:

E_ID E_Name

9 /ansen, Ola

# Svendson, Tove

; Svendson, Stephen

E 2ettersen,


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SELECT E_Name FROM Em$lo!ees_Nor+a!

6NON

SELECT E_Name FROM Em$lo!ees_6S2


E_Name

/ansen, Ola

Svendson, Tove

Svendson, Stephen

2ettersen,


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SELECT *

NTO Persons_3ac


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SQL *31T1 !T"S1 Synta+

CRE2TE D2T232SE atabase_name

*31T1 !T"S1 1+ample

'ow we want to create a database called 8my=db8.

%e use the following *31T1 !T"S1 statement:

CRE2TE D2T232SE m!_b

!atabase tables can be added with the *31T1 T"L1 statement.

SQL *31T1 T"L1 Statement

The *31T1 T"L1 Statement

The *31T1 T"L1 statement is used to create a table in a database.

SQL *31T1 T"L1 Synta+

CRE2TE T23LE table_name

(

column_name. ata_t!$e,

column_name7 ata_t!$e,

column_name8 ata_t!$e,

9999

)

The data type specifies what type of data the column can hold. >or a complete reference of all the

data types available in MS ccess, MySQL, and SQL Server, go to our complete !ata Types

reference.

*31T1 T"L1 1+ample

'ow we want to create a table called 82ersons8 that contains five columns: 2=$d, Last'ame,

>irst'ame, ddress, and *ity.

%e use the following *31T1 T"L1 statement:

CRE2TE T23LE Persons

(

P_ int,LastName %arcar(711),

http://www.w3schools.com/sql/sql_datatypes.asphttp://www.w3schools.com/sql/sql_datatypes.asphttp://www.w3schools.com/sql/sql_datatypes.asphttp://www.w3schools.com/sql/sql_datatypes.asp


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FirstName %arcar(711),

2ress %arcar(711),

Cit! %arcar(711)

)

The 2=$d column is of type int and will hold a number. The Last'ame, >irst'ame, ddress, and*ity columns are of type varchar with a ma+imum length of #II characters.

The empty 82ersons8 table will now loo6 li6e this:


The empty table can be filled with data with the $'S13T $'TO statement.

SQL *onstraints

SQL *onstraints

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

*onstraints can be specified when a table is created (with the *31T1 T"L1 statement) or after

the table is created (with the LT13 T"L1 statement).

%e will focus on the following constraints:

• 'OT 'LL

• '$Q1

• 23$M35 O31$@' LT

SQL 'OT 'LL *onstraint

"y default, a table column can hold 'LL values.


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SQL 'OT 'LL *onstraint

The 'OT 'LL constraint enforces a column to 'OT accept 'LL values.

The 'OT 'LL constraint enforces a field to always contain a value. This means that you cannot

insert a new record, or update a record without adding a value to this field.

The following SQL enforces the 82=$d8 column and the 8Last'ame8 column to not accept 'LL

values:

CRE2TE T23LE Persons

(

P_ int NOT N6LL,

LastName %arcar(711) NOT N6LL,

FirstName %arcar(711),

2ress %arcar(711),

Cit! %arcar(711))

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