An Introduction to SQL For CS420

2 Overview of SQL  It is the standard language for relational systems, although imperfect  Supports data definition (DDL) and data manipulation (DML)  DDL: CREATE TABLE, ALTER TABLE  DML: SELECT, INSERT, DELETE, UPDATE

3 Example of DDL CREATE TABLE [dbo].[S] ( [SNO] [varchar] (50) NOT NULL, [Sname] [varchar] (50) NOT NULL, [Status] [int] NOT NULL, [City] [varchar] (50) NOT NULL ) ON [PRIMARY] ALTER TABLE [dbo].[S] ADD CONSTRAINT [PK_S] PRIMARY KEY CLUSTERED ( [SNO] ) ON [PRIMARY]

4 Examples of Restrict and Project  Restrict -- List all the SNO with a Status greater than 10 Select SNO From S Where Status > 10  Project is also implemented by SELECT Select SNO, SNAME From S

5 Examples of Restrict and Project (2)  Select without duplication Select Distinct SNO From SP Select Distinct SNO From SP Order By SNO – Order By SNO DESC  Select with other conditions Select SNO From S Where city = ‘London’ and Status between 1 and 30

6 Examples of Restrict and Project (4)  Select with other conditions List the average QTY of all the shipments Select Avg(QTY) –Min, Max, Count, Sum From SP  What is the difference? Select Count (SNO) From SP Select Count (distinct SNO) – not supported by ACCESS From SP

7 Group By  Why isn’t this one correct Select SNO, Avg(QTY) From SP  GROUP BY List the average QTY for each SNO Select SNO, Avg(QTY) From SP Group By SNO

8 Group By (2)  GROUP BY List the average QTY of shipment with QTY greater than 100 for these SNO whose average QTY of shipments great than 100 is great than 500 Select SNO, Avg(QTY) From SP Where QTY > 100 Group By SNO Having Agv(QTY) > 500

9 Group By (3)  GROUP BY List, for each part, the number of Suppliers the total amount of shipment (sum of QTY). Select SNO, count(SNO) As [No of S], sum(QTY) as [Total QTY] From SP Group By SNO

10 Sub Query  GROUP BY List the supplier names for suppliers who ship ‘P2’ Select SName From S Where SNO in (select SNO from SP where PNO = ‘P2’)

11 Sub Query (2)  GROUP BY List the supplier names for suppliers who ship all parts Select SName From S Where SNO (select SNO From SP Group By SNO Having count(*) = (select count(*) from P)

12 Update operators in SQL - Insert  Insert with values INSERT INTO TEMP (PNo, Color) Values(‘P200’, ‘Green’)  Insert is implemented by INSERT INTO INSERT INTO TEMP (PNo, Color) SELECT P#, Color FROM P WHERE COLOR = ‘Red’;

13 Update operators in SQL - Delete  Delete is implemented by DELETE DELETE FROM SP WHERE PNO = ‘P2’; Deletes all shipments for part P2

14 Update operators in SQL - Update  Update is implemented by UPDATE UPDATE S SET STATUS = 2 * STATUS, CITY = ‘Rome’ WHERE CITY = ‘Paris’; Doubles the status of the Parisian suppliers and moves them to Rome.