SQL - DML. Data Manipulation Language(DML) Are used for managing data: –SELECT retrieve data from the a database –INSERT insert data into a table –UPDATE

SQL - DML

Data Manipulation Language(DML)

• Are used for managing data:– SELECT

• retrieve data from the a database

– INSERT • insert data into a table

– UPDATE • updates existing data within a table

– DELETE • deletes all records from a table

INSERT

• Simple functionality – insert a row of data into a specified table:

INSERT INTO <tableName>VALUES (<valuelist>)

• Example:INSERT INTO hotel VALUES (1,'The Pope','Vaticanstreet 1

1111 Bishopcity');

INSERT

• Things to notice about INSERT– The value list must match the field list for the

table into which the record is inserted– If we try to insert a record with a key field

which already exists, we will get an error– Null values can be inserted if the table

definition allows it– The field list can be specified explicitly

UPDATE

• Updates the value(s) for specified field(s), for the rows mathcing a given condition

UPDATE <tableName>

SET field1 = value1, field2 = value2,…

WHERE <condition>

UPDATE

• Example:

update hotel

set name ='The Great Pope'

where hotel_no= 1;

UPDATE

• Things to notice about UPDATE– For each field update, the type of the value

must match the type of the field– The WHERE clause is optional – if you leave

it out, all records in the table are updated!– It is not considered an error if zero rows are

changed, so pay attention to the condition in the WHERE clause…

Delete

• SQL syntax>– DELETE FROM table_name

WHERE some_column=some_value

• Delete all rows from GUEST : – DELETE FROM Guest;

• Delete all rooms from Hotel with Hotel_No=1:– DELETE FROM Room where Hotel_no = 1;

What if?

• Try this command: – Delete from hotel where hotel_no = 1;

• Can you delete the following tables in this order:– DELETE FROM hotel; – DELETE FROM Room;– DELETE FROM Guest; – DELETE FROM Booking;

What if?

• Example 1:update hotel

set hotel_no = 100

where hotel_no= 1;

• Example 2:update guest

set guest_no = 10

where guest_no= 1;

Exercises• With the data in place, run the below commands on the database

– INSERT INTO Hotel VALUES ( specify your own values)– INSERT INTO Room VALUES (specify your own values)– UPDATE Booking SET Price = Price* 1.30;– DELETE FROM Room WHERE (Room_no = 8)

• Now formulate commands yourself, in order to:– Insert data about ” Scandic Roskilde” in the table Hotel (you can find the

data on the Internet, or make it up yourself)– Insert data representing the fact that Hotel Scandic have 10 rooms with

room numbers 101, 102, 103, 201, 202, 203, 301, 302, 303, 400– Update the name of the Hotel ”Scandic Roskilde” to ”The new Scandic

Roskilde”– Insert data for a booking of a room at the hotel ”THe new Scandic

Roskilde”

SQL query

• An SQL query is an SQL statement, which specifies a subset of the data in the database

• A subset in terms of– Tables– Fields– Conditions on fields

HotelDB

• HOTEL: (Hotel_No, Name, Address)

• ROOM: (Room_No, Hotel_No, Types, Price)

• BOOKING: (BokingID, Hotel_No, Guest_No, Date_From, Date_To, Room_No)

• GUEST: (Guest_No, Name, Address)

Table: Guest

Guest_No Name Address

1 Eva Paradisvej 3, 1111 Bispeborg

2 Adam Paradisvej 7, 1111 Bispeborg

3 Goeg Sunset Blvd. 8, 2222 Hjemby

4 Gokke Sunset Blvd. 8, 2222 Hjemby

5 Fy Klovnevej 87, 3333 Lilleby

6 Bi Bredgade 198, 3333 Lilleby

7 Romeo Kaerlighedstunellen 1, 4444 Borgerslev

8 Julie Kaerlighedstunellen 2, 4444 Borgerslev

9 Godzilla Dommervænget 16A, 4000 Roskilde

10 KingKong Hyrdevænget 38, 4000 Roskilde

SQL query

• The most basic SQL query looks like:

SELECT <fieldlist>

FROM <tablename>

Which fields do I want

From what table do I want the fields

SELECT Guest_no, Name FROM Guest












SELECT * FROM Guest












SQL query

• A slightly more complex SQL statement looks like:

SELECT <fieldlist>

FROM <tablename>

WHERE <condition>

Which fields do I want

From what table do I want the fields

What conditions must the fields fulfill

SQL query

• The WHERE part is a logical expression, specifying conditions on certain fields

• Five fundamental types of criteria– Comparison (<, > , =)– Range (< AND >)– Set membership (belongs to a set of values)– Pattern match (for string fields)– Null (is the value of the field a null value)

Table: Guest












SELECT *FROM GuestWHERE Guest_No < 5

SQL query

• Note that we can build arbitrarily complex logical expressions, using the usual logical operators: AND, OR, NOT

• Rules are the same as for logical expres-sions in C#

• Use () to make expressions easier to read, and/or to ”overrule” evaluation rules

Table: Guest












SELECT NameFROM GuestWHERE Guest_No < 5

SQL query - range

• A range search is an SQL query where a value should be within a certain range

• Actually just a two-part comparision query

SELECT *

FROM Guest

WHERE ((Guest_no <= 6) AND (Guest_no >= 3))

SQL query - range

• Another notation for range seach uses the keyword BETWEEN

SELECT *

FROM Guest

WHERE Guest_no BETWEEN 1 AND 6

SQL query - range

• We can create a ”negated” version of a range query using NOT BETWEEN

SELECT *

FROM Guest

WHERE Guest_no NOT BETWEEN 1 AND 6

Exercise – SQL queries

• Now formulate queries yourself, in order to retrieve the below data:– Get all fields for rooms where the type is ’F’ in the hotel with

Hotel_no = 1– Get all fields for rooms that are not a ’F’ family or a ’D’ double

room– Get all bookings that are after the 15.3.2011– Get all bookings that are after the 15.3.2011 but allso before the

15.4.2011– Get all bookings for hotel_no = 1 and guest_no = 2 that are after

the 15.3.2011 but allso before the 15.4.2011 – Get all booking for Hotel_no = 2

• Formulate your queries.

SQL query – set membership

• A set membership search is an SQL query where a value must belong to a given set of values

• We use the IN keyword

SELECT *

FROM Guest

WHERE Name IN (’Adam’,’Eva’)


• Note that these two queries are equivalent

SELECT *

FROM Guest

WHERE Name IN (’Adam’,’Eva’)

SELECT *

FROM Guest

WHERE ((Name = ’Adam’) OR (Name = ’Eva’))


• We can create a ”negated” version of a set membership query using NOT IN

SELECT *

FROM Guest

WHERE Name NOT IN (’Adam’,’Eva’)

Exercise – SQL queries

• Now formulate queries yourself, in order to retrieve the below data:– Get all guests from where hotel_no 1, 3, 4 – Get all rooms from hotel_no 1 that are not a

double og family room– Get all guest that did not book a room in the

period 15.3.2011 to 15.4.2011

• Formulate your own queries

SQL query – pattern match

• A pattern match search is an SQL query where a (string) value must match a given pattern

• We use the LIKE keyword

• The hard part is choosing the correct pattern to match against – several ways to formulate a pattern


• A pattern is formulated using two special characters % and _

• % : wildcard: any sequence of zero or more characters

• _ : any single character


Pattern Meaning

’s%’ Any string starting with ’S’, of any length (at least 1)

(’super’, ’s’, ’s123’, ’s 123’)

’s_ _ _’ Any string starting with ’S’, of length exactly 4

(’such’, ’s123’, ’ssss’, ’s 1’)

’%s’ Any string ending with ’s’, of any length (at least 1)

(’Spurs’, ’s’, ’123s’, ’ s’, ’1 2s’)

’%s%’ Any string containing an ’s’, of any length (at least 1)

(’Spurs’, ’s’, ’basin’, ’ s ’, ’12s34’)

’%s_ _ _% Exercise…


SELECT *

FROM Guest

WHERE Name LIKE ’P%’

SELECT *

FROM Guest

WHERE Name LIKE ’_ _ _ _’


• We can create a ”negated” version of a pattern match query using NOT LIKE

SELECT *

FROM Hotel

WHERE Name NOT LIKE 'D%'

SQL query – null

• A null search is an SQL query where a value must be a null value

• We use the IS NULL keyword

• A null value…?

• We may allow a field to have an ”unde-fined” or null value, if it makes sense

SELECT *FROM GuestWHERE Address IS NULL


• We can create a ”negated” version of a null query using IS NOT NULL

SELECT *

FROM Guest

WHERE Address IS NOT NULL

Exercise – SQL queries• With the data in place, run the below queries on the database

– SELECT * FROM Hotel WHERE name LIKE ’%D%’– SELECT * FROM hotel WHERE Address LIKE '%n‘– SELECT * FROM Hotel WHERE Address LIKE '%_ _ _ _ _%'– SELECT * FROM Booking WHERE Date_From IS NOT NULL

• Now formulate queries yourself, in order to retrieve the below data:– Get all hotels from Roskilde– Get all hotels – Get Bookings that have a date for Date_from but not for Date_to (insert

a new row to test it)– Get all Hotels with a name starting with ’P’ and have a length of 4

characters– Get all Hotels containing a ’P’ or a ’p’

• Formulate your own queries

Documents

SQL - DML. Data Manipulation Language(DML) Are used for managing data: –SELECT retrieve data from the a database –INSERT insert data into a table –UPDATE