SQL Server Databases Tutorial

Transcription

1 SQL Server Databases Tutorial Introduction: This tutorial will help the students apply the theory they learn in the lectures using one of the most spread RDBMS which is Microso 's SQLServer. I'm using the 2012 RC0 version of SQLServer. Prerequisites: You need to install SQL Server 2012 Express edi on which is the database engine (The most important part) and also SQL server management studio which is the graphical interface that facilitates the database creation and query development and execution. They are available under these links: Under this link you have to select "express with tools" from the "select a product" drop down list and download it. Then go to same link and this time choose "SQL Server management studio" and download it. Install both packages. Notice that you need to give a name to your server, choose any oneword name and choose windows authentification so that you will not need to choose a password, when you are connected to windows, sql server considers you are the right user. This makes things much simpler for the beginner. Human Resources Database: Creating the database is quite straightforward using the SQL Server management studio. In the left pane right click on databases then click on "new database". Then click on the new database you just created then right click on "tables" an click on "new table". Then define the Employee table according to the diagram below. Then do the same thing for each table. To define a primary key, you need to select the field and click on the yellow key button that is on the upper left of the toolbox. If a key is composed of more than one field select all the fields together ( by holding the cntl key pushed) then click on the yellow key. Now you need to create relationships between each primary key with its corresponding foreign key. To do that, the simplest way is to create a diagram. So right click on database diagrams then "new database diagram". When it opens right click on the middle of the empty diagram and click on "add table". Select all the tables you created, they will be added inside the diagram. Now drag and drop the iddepartment field from the Department table on the iddep field in the Employee table, this will create the link. Do the same thing with the other relationships. ١Page

2 Employee idemployee name firstname address phone iddep Department iddepartment department Assignment idemployee idproject Project idproject projectname description PART I : Simple Queries Query Examples: 1 First queries: Populate the Department table with some data: >Insert Into Department (iddepartment, department) Values (1, 'Human Resources'); Insert Into Department (iddepartment, department) Values (2, 'Accounting'); Insert Into Department (iddepartment, department) Values (3, 'Marketing'); Select * from Department; iddepartment department 1 Human Resources 2 Accounting 3 Marketing 2 Second queries: Populate the Employee table with some data: Values (1, 'RTY', 'Salah', 'Al Aqiq', ' ', NULL); Values (2, 'UIO', 'Mounir', 'Al Hawiyya', ' ', NULL); Values (3, 'FDG', 'Qassim', 'Al Taif', ' ', NULL); Values (4, 'SDQ', 'Hafidh', 'Al Aziziyya', ' ', NULL); Select * from Employee; 1 RTY Salah Al Aqiq NULL ٢Page

3 2 UIO Mounir Al Hawiyya NULL 3 FDG Qassim Al Taif NULL 4 SDQ Hafidh Al Aziziyya NULL 3 Update employees with the department number: Update Employee Set iddep = 3 where idemployee = 1; Update Employee Set iddep = 1 where idemployee = 2; Update Employee Set iddep = 2 where idemployee = 3; Update Employee Set iddep = 3 where idemployee = 4; Select * from employee; 1 RTY Salah Al Aqiq UIO Mounir Al Hawiyya FDG Qassim Al Taif SDQ Hafidh Al Aziziyya Select queries: a Who are the employees which firstnames contain an 'a'? Select * from Employee where firstname LIKE '%a%'; 1 RTY Salah Al Aqiq FDG Qassim Al Taif SDQ Hafidh Al Aziziyya b Which employees have a name that starts with a 'Q' and contains an 's' in the third position? Select * from Employee where firstname LIKE 'Q_s%'; 3 FDG Qassim Al Taif c Which employees live in 'Al Hawiyya'? Select * from Employee where address LIKE '%Al Hawiyya%'; Or Select * from Employee where address LIKE '%Al HAwiYYA%'; 2 UIO Mounir Al Hawiyya Notice that in SQL Server using upper or lower case characters doesn't make a difference. 4 Using more than a table in queries: JOIN queries a We need to know for each employee, the name of the depatment he works in: We start by using a simple cartesian join without any filtering (no where clause): Select * from Employee As T1, Department AS T2; ٣Page

4 Note that this result is a simple product of two tables. Each line doesn't necessarily mean something. To filter only the lines that have a meaning we add to our query the where clause that will only take into account the records where iddep = iddepartment: Select * from Employee As T1, Department AS T2 Where T1.idDep = T2.idDepartment; Now we use the INNER Join: >Select * from Employee As T1 Inner join Department AS T2 Using the Outer Join: Let's add two employees without assigning them to any department: Values (10, 'TJIG', 'Mondhir', 'Makka', '456786', NULL); Values (11, 'FHTJ', 'Sabir', 'Riyadh', ' ', NULL); Now let's add a department that will not have any employee assigned to it: Insert Into Department (iddepartment, department) Values (4, 'Research and Development'); Let's see the difference between the INNER and the OUTER joins: Select * from Employee As T1 Inner join Department AS T2 ٤Page

5 If we use a left outer join: Select * from Employee As T1 Left Outer join Department AS T2 Now a right outer join: Select * from Employee As T1 Right Outer join Department AS T2 And now a Full Outer Join: Select * from Employee As T1 Full outer join Department AS T2 PART II : Transactions Now we will see how we can execute a group of queries in an atomic way : Which means all the group of queries will either be completely executed or completely canceled. All the queries inside the group will be executed without being interrupted by any other query external to that group. In other words, the state of the database between the execution of two successive queries of that group will not be accessible to anyone. This group of queries is called a transaction. The syntax of the transaction is as follows: Begin transac on T1 Query _1 Query_n ٥Page

6 Commit transac on T1; The commit keyword will lauch the execution of the sequence of queries. We can use the Rollback keyword to cancel all the sequence of queries. Now before testing these features of SQL, we need to know about the TRY/CATCH control construct. Let's look at the example: Begin TRY Begin Transaction T1 Insert into Project (idproject, projectname, description) Values (1, 'DTRG', 'this proj will...') Insert into Project (idproject, projectname, description) Values (2, 'JGHT', 'this proj will...') Insert into Project (idproject, projectname, description) Values (3, 'ERTY', 'this proj will...') Insert into Project (idproject, projectname, description) Values (4, 'VBNH', 'this proj will...') Insert into Project (idproject, projectname, description) Values (5, 'OPQS', 'this proj will...') Commit Transaction T1; End TRY Begin CATCH Rollback Transaction T1; End CATCH; How this code will be executed? First note that you have two major blocs : the BEGIN TRY End TRY : this is the TRY bloc the BEGIN CATCH End CATCH : This is the CATCH bloc This means that all that is inside the TRY bloc will be executed but if any error occurs all that is inside the CATCH bloc will be executed. So let's look at our example here: We will make five consecutive inser ons in one transac on T1. That means these five queries will only be executed when the commit transaction is encountered. But if any error occurs, then the CATCH bloc will be executed and a rollback will occur cancelling all the transaction. Let's try it to see the results of the previous code. Let's see the content of the Project table by executing a simple select * : select * from project Now we will force the previous code to make an error by trying to insert two projects with the same idproject, this should raise an error because the idproject is a primary key. Here is the modified code: Begin TRY Begin Transaction T1 Insert into Project (idproject, projectname, description) Values (6, 'FTHK', 'this proj will...') Insert into Project (idproject, projectname, description) Values (6, 'MLPO', 'this proj will...') Commit Transaction T1; End TRY Begin CATCH Rollback Transaction T1; End CATCH; ٦Page

7 We get these messages: (1 row(s) affected) (0 row(s) affected) The first message was to inform us that the first Insert was executed correctly. But when trying to execute the second Insert an error was raised because we tryed to insert another project with an idproject equal to 6. This executed the CATCH Bloc which rolledback the Transac on which gave us the second message of 0 rows affected. Note that in this case the commit transaction was not executed. After executing this code, we don't have any error message because it was caught by our CATCH bloc. But let's see the content of the project table: select * from project Now let's compare the same code without the Begin transaction Commit Rollback lines of code: First let's delete all the data from the project table: delete from project This empties the table, you can verify that by the simple select * Now let's execute this code: Begin TRY Insert into Project (idproject, projectname, description) Values (1, 'DTRG', 'this proj will...') Insert into Project (idproject, projectname, description) Values (2, 'JGHT', 'this proj will...') Insert into Project (idproject, projectname, description) Values (3, 'ERTY', 'this proj will...') Insert into Project (idproject, projectname, description) Values (4, 'VBNH', 'this proj will...') Insert into Project (idproject, projectname, description) Values (5, 'OPQS', 'this proj will...') End TRY Begin CATCH End CATCH; Note that I removed all the lines that were related to the transaction. Now let's see the data we have: select * from project ٧Page

8 OK, now we will try the same thing as previously; Inser ng two project with idproject = 6 : Begin TRY Insert into Project (idproject, projectname, description) Values (6, 'MLOP', 'this proj will...') Insert into Project (idproject, projectname, description) Values (6, 'ZSAQ', 'this proj will...') End TRY Begin CATCH End CATCH; We get these messages: (1 row(s) affected) (0 row(s) affected) But let's look at the data we now have in our table: select * from project We can see that the first project with idproject was inserted. That was the first message "1 row added". The second message "0 row added" was the answer to our second insert that didn't work. Conclusion: So now, what is the difference between the first approach (using transactions) and the second? When we had an error in the first example, the Catch bloc rolled back all the insertions. That's why we didn't have any insertion executed. But in the second example (without transactions), each insertion is executed one after the other and data is inserted in the database directly. That's why the first query executed normally and the second query didn't have any effect on the execution of the first one even if it raised an error. The use of transactions is used only when we want to make sure that either all the operations are done or they must all be cancelled if any undesirable situation occurs. ٨Page

9 PART III: Database creation and modification through SQL DDL Now let's try some DDL commands. We will create a new table with a primary key and a foreign key related to Employee.idEmployee: Use humanressources create table trial (id integer primary key not null, emp bigint foreign key references Employee(idEmployee) not null) Let's consult the new table: select * from trial Ok, the table is there but it has no data which is normal; we just created it. Now i'll simply destroy it: drop table trial Command(s) completed successfully. Now let's reexecute the select: select * from trial Msg 208, Level 16, State 1, Line 1 Invalid object name 'trial'. We got an error message telling us there is no such table called 'trial', it has been removed completely from our database. Note that this action is very dangerous as it can destroy any table with all the data it contains in just three words. To Be Continued Inchallah.. ٩Page