Database Laboratory Note (MS SQL Server 2000)

Transcription

1 Database Laboratory Note MS SQL Server 2000 Creating a New Database using QA query analyzer In MS-SQL server 2000 a database can be considered as a container to the objects in a database. A database has tables views, queries constraints etc. CREATE DATABASE <Name of Database> ON NAME = <name for the database> FILENAME = <Location> SIZE = 10, MAXSIZE = 50, FILEGROWTH = 5 LOG ON NAME = < name of log file> FILENAME = <location> SIZE = 5MB, MAXSIZE = 25MB, FILEGROWTH = 5MB The above database definition needs lots of information from the designer. If we are interested to use the default size and location of the database, then we can use the simple database definition as follows: 1. Simple Database definition Syntax: CREATE DATABASE <Name of Database> Eg. CREATE DATABASE testgroup If you execute the above statement on the query window you will see the following message The CREATE DATABASE process is allocating 0.63 MB on disk 'testgroup'. The CREATE DATABASE process is allocating 0.49 MB on disk 'testgroup_log'. This indicates that you have successfully created the database and that the data file and the log file are having the specified size of memory. You are now able to use the database. 2. Deleting a Database DROP DATABASE <Database name> Eg. DROP DATABASE testgroup 1

2 Creating tables in a database using QAquery analyzer Tables are one of the basic objects we have under a database. Tables are created using the create table statement. It requires the following things Name The name of the table to be created Field The name of the columns to be created Data type The data type of the field to be created Length The size of the data type Constraint Rules that governs the table it is optional Here the following characters are not allowed to be used for object naming. +,-,/,>,<,\,!,*,%,$,#,,,.,? white space etc Simple syntax CREATE TABLE <Table name> att1 datatype constraint, att2 datatype constraint,.. Attn datatype constraint Constraint can be primary key, not null, unique, foreign key, etc. constraints are optional. If you have you can use it if not you can leave the space empty. The primary key constraint: is an entity constraint which is used to assign a field as a key of that table. In the above syntax you van only assign a single field as a primary key. If you have a composite key as a primary key see the section constraints. The not null constraint: is a constraint on a specific field and is used to enforce that field not to be empty at the time of data entry. The default here is null i.e. you can enter a data for that field or you can leave it empty The unique constraint: is a constraint on a specific field which is used to make a certain field. 2

3 Here is an example of creating a table without any constraint. Eg. CREATE TABLE teststudent id_no char12, F_name char20, Lname char20, Sex char6, E_year int The above table will be successfully executed. But the table will not be a valid table in relational database system. It violates the primary key constraint thus we need to add constraints. The detail syntax to create a table with its primary key is. 3. Creating a Table with Primary Key Constraint create table Department DID char5 primary key, Name char10 not null, Loc char10 The above table Department will consider DID as a primary key and Name can not take null and Loc has no constraints. 4. Creating a Table with more than one attribute as a Primary Key create table Loan MID char3 not null, CID char3 not null, BDate datetime not null, DDate datetime, Constraint Pk_Loan Primary Key MID,CID,BDate The above table Loan will consider MID, CID and BDate together as a primary key. 3

4 5. Creating a Table with Primary Key and Foreign Key Primary key candidate key foreign key attributes are used to create relationship between tables so that cross referencing can be used to retrieve interrelated tuples from the tables. The General syntax would be: CREATE TABLE <Table name> att1 datatype PRIMARY KEY, att2 datatype constraint,. attn datatype constraint, FOREIGN KEY Atti REFERENCES <home tableatt> the last line can be changed to the following if we want to assigne a user defined name for the constraint Constraint ConstName foreign key attribute references hometableattribute Eg: Assuming that the Department and Employee table are related with each other where the Department Id DID is primary key attribute posted in Employee table as a foreign key with the name EDID. The coding method will be. create table Department DID char5 primary key, Name char10 not null, Loc char10 create table Employee E ID char5 primary key, FName char10 not null, LName char10 not null, Salary money. EDID char5 foreign key references DepartmentDID 4

5 or create table Employee E ID char5 primary key, FName char10 not null, LName char10 not null, Salary money. EDID char5, foreign key EDID references DepartmentDID Or the above Employee table can be changed to create table Employee E ID char5 primary key, FName char10 not null, LName char10 not null, Salary money. EDID char5, Constraint Fk_Emp foreign key EDID references DepartmentDID 6. Altering a table to change data definition of the table One can change the table definition after creating the table. The kind of change might be: Adding a new attribute to an existing table Deleting and existing attribute from an existing table Changing the datatype and size of an existing attribute Adding more constraints to an existing attribute of a table like not null. create table Employee E ID char5 primary key, FName char10 not null, LName char10 not null, Salary money 5

6 7. Add Column/Attribute to an existing table Syntax: ALTER TABLE <table name> ADD <column name> <data type> <constraint> Adding DateOfBirth in Employee Table ALTER TABLE Employee ADD DoB Datetime After this instruction is executed, the employee table will have the following schema. EID FName LName Salary DoB 8. Delete a Column/Attribute from an existing table Syntax: ALTER TABLE <table name> DROP <column name> Deleting Date of Birth Dob from Employee Table ALTER TABLE Employee DROP COLUMN DoB If an attribute a column have a constraint, we can not delete is by using the above query, instead we have to first drop/delete the constraint on the attribute column. For example, to delete an attribute which is a Primary Key, first the primary key constraint should be dropped before trying to delete the table. In the next table, the primary key are MID,CID,BDate with constraint name Pk_Loan. Then, if we want to delete the MID attribute, we can not simply drop it before lifting the constraint on it. Thus first the Pk_Loan should be deleted and then MID can be deleted. create table Loan MID char3 not null, CID char3 not null, BDate datetime not null, DDate datetime, Constraint Pk_Loan Primary Key MID,CID,BDate Thus: Alter Table Loan Drop Constraint Pk_Loan Alter Table Loan Drop Column MID 6

7 9. Change Definition of a Column/Attribute in a Table Syntax: ALTER TABLE <table name> ALTER COLUMN <column name> <New data type> <New Size> <New Constraint> Eg: to change the size of Name in the Department table above from 10 to 15 char ALTER TABLE Employee ALTER COLUMN FName char15 not null 10. Insert values for an Existing table Inserting values to a table without codes To inserting values to a table without codes, open the table in the Enterprise Manager and insert a value in the column and move to the next using TAB key. Inserting values to a table using codes in Query Analyzer Syntax: INSERT INTO <Table name> VALUES values separated by a comma In the insert into command, the number of values in the curve bracket should match with the number of attributes of the target table. In addition, character data values should be embraced within single quote. Inserting one tuple in Employee table Eg: INSERT INTO Employee VALUES 'E01','Abebe', Taye, 1250 For multiple tuple insertion, one has to repeatedly execute the above code with different values. 11. Add Constraint to an existing table After a table is created one can add constraints or delete constraints to the existing table. Constraints might be: Primary Key, Foreign Key, Null, Check, etc. The general syntax would be: ALTER TABLE <table name> ADD CONSTRAINT <constraint name> <constraint> a Add Primary Key Constraint Syntax: ALTER TABLE <table name> ADD CONSTRAINT <constraint name> Primary Key <attribute name> E.g.: ALTER TABLE Employee ADD CONSTRAINT PK_SupID Primary Key EID 7

8 b Add Foreign Key Constraint Syntax: ALTER TABLE <table name> ADD CONSTRAINT <constraint name> Foreign Key <attribute name> references <table name><attribute name> Eg: ALTER TABLE Employee ADD CONSTRAINT FK_DID Foreign Key DID References DepartmentDID 12. Viewing the content of a table The SELECT statement is used to display the content or part of a table in a table form. Most commonly used parts of the SELECT statement is the following: SELECT <field list> FROM <tables> WHERE <condition> GROUP BY <field> HAVING <aggregate condition> Simple select statement Employee where the asterisk * means all the attributes from employee table. SELECT EID,FName,Slary FROM Employee Contains only the three attributes from employee table in the result. Employee WHERE Salary>1000 Displays, tuples from the Employee table whose value for the salary attribute is greater than 1000 To display attributes from more than one table Employee, Department WHERE Employee.EDID=Department.DID The condition of selection is the equality between primary key and foreign key attributes from the two related tables. But instead of using the long able name in the condition, we can represent the table names by a variable which is called alias. 8

9 Thus the above SQL command will be: Employee E, DepartmentD WHERE E.EDID=D. DID Or, if we want to select only some of the attributes from the two tables. SELECT E.EID,E.FName,E.Lname,D.NameFROM Employee E, Department D WHERE E.EDID=D. DID In the select statement inbuilt functions like count COUNT, maximum MAX, minimum MIN, average AVG, total SUM, etc can be used, where in such cases the group by phrase will be used. To displays the maximum salary from each department SELECT DID, MAXsalary FROM Employee GROUP BY EDID To displays the average salary from each department SELECT DID, AVGsalary FROM Employee GROUP BY EDID To count the number of employees in each department SELECT DID, MAXEID FROM Employee GROUP BY EDID For the new attribute created, we can give new attribute name using alias method. SELECT DID, AVGsalary AS Avg_Salary FROM Employee GROUP BY EDID We can also sort the result using one of the attributes in the result using the ORDER BY clause. Employee WHERE Salary>1000 ORDER BY FName 13. Deleting tuples from a table To delete the whole content of a tuple from an existing table we will use the DELETE command. General synax: DELETE <TableName> WHERE <Condition> To delete and employee with first name abebe DELETE employee WHERE FName='Abebe' 9

10 To delete an employee with employee id e05 DELETE employee WHERE EID='e05' If we use the delete statement without the where clause without the condition, all tuples of the table will be deleted and we will have an empty table. DELETE employee The above command will delete all the tuples in the employee table but NOT the table. 14. Modifying attribute values of a tuple To modify or update attribute values of tuples in an existing table we will use the UPDATE command. General synax: UPDATE <TableName> SET <AtrributeName=value> WHERE <Condition> To increase the salary of all employees by 5% UPDATE Employee SET Salary=Salary*1.05 To increase the salary of only one employee with id e06 by 15% UPDATE Employee SET Salary=Salary*1.05 WHERE EID= e06 To increase the salary of all employees earning a slary less than 1000 by 25% UPDATE Employee SET Salary=Salary*1.25 WHERE salary< Creating a view or virtual table In SQL, a VIEW is a virtual table based on the result-set of a SELECT statement. A view contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database. You can add SQL functions, WHERE, and JOIN statements to a view and present the data as if the data were coming from a single table. Note: The database design and structure will NOT be affected by the functions, where, or join statements in a view. 10

11 General Syntax CREATE VIEW <View_Name> AS SELECT <attribute List> FROM <Table_Name> WHERE <Condition> Note: The database does not store the view data! The database engine recreates the data, using the view's SELECT statement, every time a user queries a view. To create a virtual table or a view which will display the list of employees whose salary is greater than 100, the view will be: CREATE VIEW Emp_Sal_1000 AS SELECT * FROM Employee After this query is executed, we can run the following query, as it acts just like a normal table in the database. Emp_Sal_1000 To create a view that contains the average salary of employees in each department. CREATE VIEW Avg_Salary_Dept AS SELECT DID, AVGsalary FROM Employee GROUP BY EDID Generally, any select statement can be used to from a view, where then after the view can be used as a normal table. A view can also be used in other queries as a normal table. 11

12 16. Joining tables Joining tables is similar with combining tables using the select statement where in the condition we use equality between primary key attributes and foreign key attributes. When it comes to JOIN, we will use the clause JOIN with different variety of joins like INNER, RIGHT OUTER, LEFT OUTER, etc. in addition all the issues we have seen fro select statement and create view can be implemented using the join query. One can use join in normal select statement. One can also use join in creating a view. The General Syntax: SELECT <attribute List> FROM <table1> [ JOIN TYPE ] <table2> ON <Join condition> WHERE <additional Condition> There are different types of join. 1. Inner Join Joins the tables using equality between the attributes of primary key and foreign key columns where only tuples participating on the relationship are included in the result. SELECT <attribute List> FROM <table1> INNER JOIN <table2> ON <Join condition> WHERE <additional Condition> 2. Left Join Joins the tables using equality between the attributes of primary key and foreign key columns and also includes tuples from the table in the left in the result even if they don t participate in the relationship. For attributes from the table in the right side the value null will be field for those tuples from the left side not participating in the relationship. SELECT <attribute List> FROM <table1> LEFT JOIN <table2> ON <Join condition> WHERE <additional Condition> 12

13 3. Right Join Joins the tables using equality between the attributes of primary key and foreign key columns and also includes tuples from the table in the right side in the result even if they don t participate in the relationship. For attributes from the table in the left side the value null will be field for those tuples from the right side not participating in the relationship. SELECT <attribute List> FROM <table1> RIGHT JOIN <table2> ON <Join condition> WHERE <additional Condition> 4. Full Join Joins the tables using equality between the attributes of primary key and foreign key columns and also includes tuples from both tables in the result even if they don t participate in the relationship. For attributes from the table in the left side the value null will be field for those tuples from the table in the right side not participating in the relationship. And For attributes from the table in the right side the value null will be field for those tuples from the table in the left side not participating in the relationship. SELECT <attribute List> FROM <table1> FULL JOIN <table2> ON <Join condition> WHERE <additional Condition> 13

14 Sample tables and Examples to elestrate the join types. EMPLOYEE EID FName LName Salary EDID e01 Abebe Taye d01 e02 bekele mamo d03 e03 Almaz mitiku d02 E04 hirut seleshi d01 E05 mammo mesfin d03 E06 mahlet takele NULL E07 belay Kebede NULL DEPARTMENT DID DName DLoc D01 Finanace B05 D02 Personnel B04 D03 sales B03 D04 Project B07 D05 Mang B01 Inner Join employee INNER JOIN department ON employee.edid=department.did Or using the alias method employee E INNER JOIN department D ON E.edid=D.did The above two SQL queries will produce the following table EID FName LName Salary EDID DID DName DLoc e01 Abebe Taye d01 d01 Finanace B05 e02 Bekele mamo d03 d03 Sales B03 e03 Almaz mitiku d02 d02 Personnel B04 e04 hirut seleshi d01 d01 Finanace B05 e05 mammo mesfin d03 d03 Sales B03 14

15 Left Join Left Outer Join employee LEFT JOIN department ON employee.edid=department.did employee LEFT OUTER JOIN department ON employee.edid=department.did Or using the alias method employee E LEFT JOIN department D ON E.edid=D.did employee E LEFT OUTER JOIN department D ON E.edid=D.did The above four SQL queries will produce the following table EID FName LName Salary EDID DID DName DLoc e01 Abebe Taye d01 d01 Finanace B05 e02 bekele mamo d03 d03 sales B03 e03 Almaz mitiku d02 d02 Personnel B04 e04 hirut seleshi d01 d01 Finanace B05 e05 mammo mesfin d03 d03 sales B03 e06 mahlet takele NULL NULL NULL NULL e07 belay Kebede NULL NULL NULL NULL 15

16 Right Join Right Outer Join employee RIGHT JOIN department ON employee.edid=department.did employee RIGHT OUTER JOIN department ON employee.edid=department.did Or using the alias method employee E RIGHT JOIN department D ON E.edid=D.did employee E RIGHT OUTER JOIN department D ON E.edid=D.did The above four SQL queries will produce the following table EID FName LName Salary EDID DID DName DLoc e01 Abebe Taye d01 d01 Finanace B05 e04 hirut seleshi d01 d01 Finanace B05 e03 Almaz mitiku d02 d02 Personnel B04 e02 bekele mamo d03 d03 sales B03 e05 mammo mesfin d03 d03 sales B03 NULL NULL NULL NULL NULL d04 Project B07 NULL NULL NULL NULL NULL d05 Mang B01 16

17 Full Join Full Outer Join employee FULL JOIN department ON employee.edid=department.did employee FULL OUTER JOIN department ON employee.edid=department.did Or using the alias method employee E FULL JOIN department D ON E.edid=D.did employee E FULL OUTER JOIN department D ON E.edid=D.did The above four SQL queries will produce the following table EID FName LName Salary EDID DID DName DLoc e06 mahlet takele NULL NULL NULL NULL e07 belay Kebede NULL NULL NULL NULL e01 Abebe Taye d01 d01 Finanace B05 e04 hirut seleshi d01 d01 Finanace B05 e03 Almaz mitiku d02 d02 Personnel B04 e02 bekele mamo d03 d03 sales B03 e05 mammo mesfin d03 d03 sales B03 NULL NULL NULL NULL NULL d04 Project B07 NULL NULL NULL NULL NULL d05 Mang B01 17