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 VALUES ( ) Example: INSERT INTO hotel VALUES (1,'The Pope','Vaticanstreet 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 SET field1 = value1, field2 = value2,… WHERE

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_NoNameAddress 1EvaParadisvej 3, 1111 Bispeborg 2AdamParadisvej 7, 1111 Bispeborg 3GoegSunset Blvd. 8, 2222 Hjemby 4GokkeSunset Blvd. 8, 2222 Hjemby 5FyKlovnevej 87, 3333 Lilleby 6BiBredgade 198, 3333 Lilleby 7RomeoKaerlighedstunellen 1, 4444 Borgerslev 8JulieKaerlighedstunellen 2, 4444 Borgerslev 9GodzillaDommervænget 16A, 4000 Roskilde 10KingKongHyrdevænget 38, 4000 Roskilde

SQL query The most basic SQL query looks like: SELECT FROM Which fields do I want From what table do I want the fields

SELECT Guest_no, Name FROM Guest Guest_NoNameAddress 1EvaParadisvej 3, 1111 Bispeborg 2AdamParadisvej 7, 1111 Bispeborg 3GoegSunset Blvd. 8, 2222 Hjemby 4GokkeSunset Blvd. 8, 2222 Hjemby 5FyKlovnevej 87, 3333 Lilleby 6BiBredgade 198, 3333 Lilleby 7RomeoKaerlighedstunellen 1, 4444 Borgerslev 8JulieKaerlighedstunellen 2, 4444 Borgerslev 9GodzillaDommervænget 16A, 4000 Roskilde 10KingKongHyrdevænget 38, 4000 Roskilde

SELECT * FROM Guest Guest_NoNameAddress 1EvaParadisvej 3, 1111 Bispeborg 2AdamParadisvej 7, 1111 Bispeborg 3GoegSunset Blvd. 8, 2222 Hjemby 4GokkeSunset Blvd. 8, 2222 Hjemby 5FyKlovnevej 87, 3333 Lilleby 6BiBredgade 198, 3333 Lilleby 7RomeoKaerlighedstunellen 1, 4444 Borgerslev 8JulieKaerlighedstunellen 2, 4444 Borgerslev 9GodzillaDommervænget 16A, 4000 Roskilde 10KingKongHyrdevænget 38, 4000 Roskilde

SQL query A slightly more complex SQL statement looks like: SELECT FROM WHERE 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 ( ) –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 Guest_NoNameAddress 1EvaParadisvej 3, 1111 Bispeborg 2AdamParadisvej 7, 1111 Bispeborg 3GoegSunset Blvd. 8, 2222 Hjemby 4GokkeSunset Blvd. 8, 2222 Hjemby 5FyKlovnevej 87, 3333 Lilleby 6BiBredgade 198, 3333 Lilleby 7RomeoKaerlighedstunellen 1, 4444 Borgerslev 8JulieKaerlighedstunellen 2, 4444 Borgerslev 9GodzillaDommervænget 16A, 4000 Roskilde 10KingKongHyrdevænget 38, 4000 Roskilde SELECT * FROM Guest WHEREGuest_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 Guest_NoNameAddress 1EvaParadisvej 3, 1111 Bispeborg 2AdamParadisvej 7, 1111 Bispeborg 3GoegSunset Blvd. 8, 2222 Hjemby 4GokkeSunset Blvd. 8, 2222 Hjemby 5FyKlovnevej 87, 3333 Lilleby 6BiBredgade 198, 3333 Lilleby 7RomeoKaerlighedstunellen 1, 4444 Borgerslev 8JulieKaerlighedstunellen 2, 4444 Borgerslev 9GodzillaDommervænget 16A, 4000 Roskilde 10KingKongHyrdevænget 38, 4000 Roskilde SELECT Name FROM Guest WHEREGuest_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 = 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 –Get all bookings that are after the but allso before the –Get all bookings for hotel_no = 1 and guest_no = 2 that are after the but allso before the –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’)

SQL query – set membership Note that these two queries are equivalent SELECT * FROM Guest WHERE Name IN (’Adam’,’Eva’) SELECT * FROM Guest WHERE ((Name = ’Adam’) OR (Name = ’Eva’))

SQL query – set membership 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 to 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

SQL query – pattern match A pattern is formulated using two special characters % and _ % : wildcard: any sequence of zero or more characters _ : any single character

SQL query – pattern match PatternMeaning ’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…

SQL query – pattern match SELECT * FROM Guest WHERE Name LIKE ’P%’ SELECT * FROM Guest WHERE Name LIKE ’_ _ _ _’

SQL query – pattern match 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 Guest WHERE Address IS NULL

SQL query – pattern match 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