The Islamic University of Gaza Faculty of Engineering Department of Computer Engineering ECOM 4113: Database Lab Lab # 2 Data Definition Language (DDL) Eng. Alaa O Shama October, 2015
Objective To be familiar with SQL Language especially with Data Definition Language(DDL). Relational Database (RDB) Relational Database means data stored in relations. Relation is essentially a mathematical term for table. Each table is a named collection of rows (tuples). Each row of a given table has the same set of named Columns (attributes), and each column is of a specific data type. Database Keys A key is a logical way to access a record in a table. There are many types of key in RDB: Candidate Key A candidate key is any field, or combination of fields, that uniquely identifies a record. The field/s of the candidate key must contain unique values, and can't contain a null value. Primary Key (PK) A primary key is the candidate key that has been chosen to identify unique records in a particular table. Foreign Key (FK) A relationship between two tables is created by creating a common field to the two tables. The common field must be a primary key to the one table.
SQL Language SQL is presently expanded as Structured Query Language. Originally, SQL was called SEQUEL. SQL is now the standard language for commercial relational DBMSs. SQL Statements SQL has insensitive statements for data definitions, queries, and updates. SQL commands are grouped into major categories depending on their functionality: Data Definition Language (DDL): These SQL commands are used for creating,modifying, and dropping the structure of database objects. It also defines keys, specify links between tables, and impose constraints between tables. The commands are ALTER, ANALYZE, AUDIT, COMMENT, CREATE,DROP,FLASHBACK, GRANT, PURGE, RENAME, REVOKE and TRUNCATE. Data Manipulation Language (DML): These SQL commands are used for storing, retrieving, modifying, and deleting data. These Data Manipulation Language commands are CALL, DELETE, EXPLAIN,INSERT, LOCK TABLE, MERGE, SELECT and UPDATE. Transaction Control Language (TCL): These SQL commands are used for managing changes affecting the data. These commands are COMMIT, ROLLBACK, and SAVEPOINT. In this lab, we will concentrate on DDL. Schema Creating To create a new schema in default XE database, we have to create a new user and the Oracle creates a schema for that user with the same name.
To create a new user, you have to follow the next steps: 1- Connect to XE database by SYSTEM user. 2- Expand the connection and R-click on other users >> Create User. 3- User tab >> enter user name and password and choose the default and temporary table spaces.
4- System Privileges tab >> Grant the necessary privileges for the user. Granted Privileges: Create session: to be able to connect to XE database by the new user Create table/ view/ procedure/ synonym/ sequence/ trigger/ type/materialized view: to be able to create tables, views, procedure,synonyms, sequences, user defined data types and materialized views respectively inside the new schema. Unlimited tablespace: to permit a user to use an unlimited amount of any tablespace in the database. Alter session: to set or modify any of the conditions or parameters that affect your connection to the database. 5- Apply
6- You can create a new user by SQL commands. Create User Create User user_name identified by password Default tablespace tablespace Temporary tablespace tablespace ; Privileges Grant Privilige To user_name ; On the worksheet of SYSTEM connection, write the following statements and execute them.
7- After user creation, Connect to XE database by the new user. 8- Now you can issue SQL statements for the new schema.
Table Creating DATA TYPES NUMERIC TYPES Name Description Range Number [(p[, s])] User-specified precision, scale. The precision is the number of digits to both sides of the decimal point. The positive scale is the count of decimal digits in the fractional part, to the right of the decimal point. If the scale of a value to be stored is greater than the declared scale of the column, the system will round the value to the specified number of fractional digits. When the scale is positive and the number of digits to the left of the decimal point exceeds (p-s), an error is raised. Integer INT Number(p) = Number(p,0) s=0. Number: specifies the maximum range and precision for an Oracle number. Number (32) The precision p can range from 1 to 38. The scale s can range from -84 to 127. A NUMBER value requires from 1 to 22 bytes. -2 ^31 (2 ^31)-1
CHARACTER TYPES Definition Description Notes char A single character. Char (n[byte char]) NCHAR[(n)] VARCHAR2(n [byte char]) NVARCHAR2(n) A set of characters exactly n characters in length, padded with spaces. If you attempt to store a string that is too long, an error will be generated. DATE/TIME DATA TYPES A fixed length Unicode character string having maximum length n characters. Default and minimum n is 1 character. A Variable length character string having maximum length n bytes or characters. You must specify size for VARCHAR2. Minimum size is 1 byte or 1 character. A Variable length Unicode character string having maximum length n characters. You must specify size for NVARCHAR2. To specify a value to character data types, it is placed between single quotation marks ( ), and it is a case sensitive, e.g., Hello. Use concatenation operator ( ) to concatenate two strings, e.g. abc def results abcdef. Name Description Notes Example Date timestamp [(p)] Date Only. Its components are YEAR, MONTH, and DAY. The default format is: DD-MON-YY. SYSDATE: special value that is current system date. Includes the DATE and TIME fields, with a blank space between two fields. The Default format is: DD-MON-YY HH.MM.SS.p AM/PM To specify a value to Date types, you can: Place the value between single quotation marks in DD-MON-YY/YYYY format. Use Date keyword and YY/YYYY-MM-DD Format. To specify a value for Timestamps DataType, you can: Place the value in ( ) mark In DD-MON-YY HH:MM:SS.p [AM/PM] 31-MAY-02 31-MAY-2002 Date 2002-05-31 Date 02-05-31 31-MAY-02 10:30:56 31-MAY-02 10:30:56 PM Timestamp 2002-05-02 10:30:56.25
Timestamp [(p)] with time zone Timestamp with time zone displacement value. The Default format is: DD-MON-YY HH.MM.SS.p AM/PM +/- HH:MM/time zone [+/-HH:MM/time zone] Format. Hour from (1-12). +/-HH:MM/time zone for timestamp with time zone data type. AM/PM required for timestamp with time zone data type. If you don t specify AM/PM for timestamp and timestamp with local time zone data types the default is AM. 31-MAY-03 10:30:56 AM +08:00 '04-Jul-05 4:5:6 PM ASIA/JERUSALEM' Timestamp 2002-05-02 15:30:56.36-07:00 Timestamp 2002-05-02 15:30:56.36 ASIA/JERUSALEM' Default Values A column can be assigned a default value. When a new row is created and no values are specified for some of the columns, those columns will be filled with their respective default values. If no default value is declared explicitly, the default value is the null value. In a table definition, default values are listed after the column data type. CREATE TABLE EMPLOYEE (.. Salary number (6,2) Default 2000,. ); Constraints SQL allows you to define constraints on columns and tables. Constraints give you as much control over the data in your tables as you wish. If a user attempts to store data in column that would violate a constraint, an error is raised.
Constraints Types: NOT NULL: prohibits a database value from being null. Unique:prohibits multiple rows from having the same value in the same column or combination of columns but allows some values to be null. Primary key:combines a NOT NULL constraint and a unique constraint in a si ngle declaration. It prohibits multiple rows from having the same value in the same column or combination of columns and prohibits values from being null. Check: requires a value in the database to comply with a specified condition. Foreign key: requires values in one table to match values in another table. You can define constraints syntactically in two ways: As a part of the definition of an individual column or attribute. This is called in-line specification. As a part of the table definition. This is called out-of-line specification. Notes: NOT NULL constraints must be declared inline. All other constraints can be declared either inline or out of line. The constraint on a combination of columns must be declared out of line. You cannot designate the same column or combination of columns as both a primary key and a unique key. In Line Specification [Constraint const_name] const_type [const_specifications] Note: In this specification const_type doesn t specified for foreign key constraint. Out Of Line Specification [Constraint const_name] const_type (column[s]) [const_specifications]
Constraint const_name specifies a name for the constraint. If you omit this identifier, then Oracle Database generates a name. Constraint name clarifies error messages and allows you to refer to the constraint when you need to change it. Not Null Constraint It must be declared in line. In Line Specification [Constraint const_name] Not Null Unique Constraint In Line Specification [Constraint const_name] Unique Out of Line Specification [Constraint const_name] Unique (Column[s]) Primary Key Constraint In Line Specification [Constraint const_name] Primary Key Out of Line Specification [Constraint const_name] Primary Key (Column[s]) Check Constraint In Line & Out Of Line Specifications [Constraint const_name] ckeck (Boolean Expression)
Foreign Key Constraint A foreign key constraint specifies that the values in a column (or a group of columns) must match the values appearing in some row of another table. This maintains the referential integrity between two related tables. When Deleting or updating a referenced row, Oracle allows you to handle that as well. There are two options: CASCADE if you want Oracle to remove/update dependent foreign key values. SET NULL if you want Oracle to convert dependent foreign key values to NULL. In Line Specification [Constraint const_name] references ReferencedTable (ReferencedCol) [ON Delete set Null CASCADE] [ON UPDATE set NULL CASCADE] Out Of Line Specification [Constraint const_name] foreign key (Column[s]) references ReferencedTable (ReferencedCol[s]) [ON Delete set Null CASCADE] [ON UPDATE set NULL CASCADE] If you omit ON DELETE or ON UPDATE clause, then Oracle does not allow you to delete or update referenced key values in the parent table that have dependent rows in the child table. Note: Foreign key column data type must be as same as referenced column.
Example: Modifying Tables Alter Table command allow you to alter the definition, or structure, of the table, such you can: Add columns. Remove columns. Add constraints. Remove constraints. Change default values. Change column data types. Rename columns. Rename tables.
Add Columns ADD( Col1Name DataType [Default value] [Constraints], Col2Name DataType [Default value] [Constraints] ); Change Column Data Type MODIFY ColName newdatatype; Note: You can change the data type of any column if all rows of the column contain nulls. Specify Column Default Value MODIFY ColName DEFAULT DefValue; To discontinue previously specified default values,so that they are no longer automatically inserted into newly added rows, replace the values with NULL. Remove Default Value MODIFY ColName DEFAULT NULL; Rename Column Rename Column oldname to newname;
Remove Column Drop Column ColName [CASCADE]; CASCADE: if you want to drop everything that depends on the column. Add Out Of Line Constraint Add OutOfLineConstraint ; To add a not null constraint, which cannot be written as out of line constraint use this syntax: Add Not Null Constraint Modify ColName Not Null; Rename Constraint RENAME CONSTRAINT OldName TO NewName; Remove Constraint DROP CONSTRAINT name [CASCADE]; Remove Not Null Constraint MODIFY ColName NULL;
ReName Table RENAME TO NewName; Remove Table DROP TABLE TName [CASCADE]; Notes: SQL Statements are executed sequentially. To run a statement,put the cursor on the statement and press Ctrl+Enter or click To run more than one statement sequentially, select them then click on icon. You can run all statements in the worksheet, put the cursor on the first statement and press F5. Or click on icon. Example: You have the following COMPANY Schema, create it on Oracle.
Solution: Note: Dno is a foreign key references the Department table but we haven t created DEPARTMENT table yet, so we can t add foreign constraint here, and we need to alter EMPLOYEE table to add the foreign constraint after DEPARTMENT creating.
Exercise: 1. Create the following Library schema.
Homework : Create Mail Order Schema.