Creating and Managing Tables 14

ObjectivesObjectives After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Describe the main database objects Describe the main database objects Create tables Create tables Describe the datatypes that can be used when specifying column definition Describe the datatypes that can be used when specifying column definition Alter table definitions Alter table definitions Drop, rename, and truncate tables Drop, rename, and truncate tables After completing this lesson, you should be able to do the following: After completing this lesson, you should be able to do the following: Describe the main database objects Describe the main database objects Create tables Create tables Describe the datatypes that can be used when specifying column definition Describe the datatypes that can be used when specifying column definition Alter table definitions Alter table definitions Drop, rename, and truncate tables Drop, rename, and truncate tables

Database Objects ObjectDescription TableBasic unit of storage; composed of rows and columns View Logically represents subsets of data from one or more tables Sequence Generates primary key values IndexImproves the performance of some queries Synonym Gives alternative names to objects

Naming Conventions Must begin with a letter Must begin with a letter Can be 1 – 30 characters long Can be 1 – 30 characters long Must contain only A – Z, a – z, 0 – 9, _, $, and # Must contain only A – Z, a – z, 0 – 9, _, $, and # Must not duplicate the name of another object owned by the same user Must not duplicate the name of another object owned by the same user Must not be an Oracle Server reserved word Must not be an Oracle Server reserved word Must begin with a letter Must begin with a letter Can be 1 – 30 characters long Can be 1 – 30 characters long Must contain only A – Z, a – z, 0 – 9, _, $, and # Must contain only A – Z, a – z, 0 – 9, _, $, and # Must not duplicate the name of another object owned by the same user Must not duplicate the name of another object owned by the same user Must not be an Oracle Server reserved word Must not be an Oracle Server reserved word

Naming Guidelines Use descriptive names for tables and other database objects. Name the same entity consistently in different tables. For example, the department number column is called DEPTNO in both the EMP table and the DEPT table.

The CREATE TABLE Statement You must have : You must have : CREATE TABLE privilege CREATE TABLE privilege A storage area A storage area You specify: You specify: Table name Table name Column name, column datatype, and column size Column name, column datatype, and column size You must have : You must have : CREATE TABLE privilege CREATE TABLE privilege A storage area A storage area You specify: You specify: Table name Table name Column name, column datatype, and column size Column name, column datatype, and column size CREATE TABLE [schema.]table (column datatype [DEFAULT expr][,...]);

SQL> create table demo.Student (Stno Number(10), Stname Varchar(40), Mark 2 Number(3)); SQL> insert into demo.Student 2 values ( , 'Ahmad', 77); تم تكوين صف واحد SQL> insert into demo.student 2 values( , 'Mostafa', 87); تم تكوين صف واحد SQL> insert into demo.student 2 values( , 'Ibraheem', 46);

Referencing Another User ’ s Tables Tables belonging to other users are not in the user ’ s schema. Tables belonging to other users are not in the user ’ s schema. You should use the owner ’ s name as a prefix to the table. You should use the owner ’ s name as a prefix to the table. Tables belonging to other users are not in the user ’ s schema. Tables belonging to other users are not in the user ’ s schema. You should use the owner ’ s name as a prefix to the table. You should use the owner ’ s name as a prefix to the table.

The DEFAULT Option Specify a default value for a column during an insert. Specify a default value for a column during an insert. … hiredate DATE DEFAULT SYSDATE, … Legal values are literal value, expression, or SQL function. Illegal values are another column ’ s name or pseudocolumn. The default datatype must match the column datatype. Legal values are literal value, expression, or SQL function. Illegal values are another column ’ s name or pseudocolumn. The default datatype must match the column datatype.

SQL> create table demo.Exam (Stno Number(10), 2 Stname Varchar(40), Mark Number(3), 3 Hiredate date default sysdate); SQL> insert into demo.exam (stno, stname, mark) 2 values ( , 'Ahmad', 77); SQL> insert into demo.exam (stno, stname, mark) 2 values( , 'Mostafa', 87); SQL> insert into demo.exam (stno, stname, mark) 2 values( , 'Ibraheem', 46);

Creating Tables SQL> CREATE TABLE dept 2(deptno NUMBER(2), 3 dname VARCHAR2(14), 4 loc VARCHAR2(13)); Table created. Create the table. Create the table. Confirm table creation. SQL> DESCRIBE dept Name Null? Type DEPTNO NUMBER(2) DNAME VARCHAR2(14) LOC VARCHAR2(13)

Tables in the Oracle Database User Tables User Tables Collection of tables created and maintained by the user Collection of tables created and maintained by the user Contain user information Contain user information Data Dictionary Data Dictionary Collection of tables created and maintained by the Oracle server Collection of tables created and maintained by the Oracle server Contain database information Contain database information User Tables User Tables Collection of tables created and maintained by the user Collection of tables created and maintained by the user Contain user information Contain user information Data Dictionary Data Dictionary Collection of tables created and maintained by the Oracle server Collection of tables created and maintained by the Oracle server Contain database information Contain database information

Querying the Data Dictionary Describe tables owned by the user. Describe tables owned by the user. View distinct object types owned by the user. View tables, views, synonyms, and sequences owned by the user. SQL> SELECT* 2FROMuser_tables; SQL> SELECTDISTINCT object_type 2FROM user_objects; SQL> SELECT* 2FROMuser_catalog;

DatatypesDatatypes DatatypeDescription VARCHAR2(size)Variable-length character data CHAR(size) Fixed-length character data NUMBER(p,s) Variable-length numeric data DATE Date and time values LONG Variable-length character data up to 2 gigabytes CLOBSingle-byte character data up to 4 gigabytes RAW and LONG RAW Raw binary data BLOBBinary data up to 4 gigabytes BFILEBinary data stored in an external file; up to 4 gigabytes

Creating a Table by Using a Subquery Create a table and insert rows by combining the CREATE TABLE statement and AS subquery option. Create a table and insert rows by combining the CREATE TABLE statement and AS subquery option. Match the number of specified columns to the number of subquery columns. Match the number of specified columns to the number of subquery columns. Define columns with column names and default values. Define columns with column names and default values. Create a table and insert rows by combining the CREATE TABLE statement and AS subquery option. Create a table and insert rows by combining the CREATE TABLE statement and AS subquery option. Match the number of specified columns to the number of subquery columns. Match the number of specified columns to the number of subquery columns. Define columns with column names and default values. Define columns with column names and default values. CREATE TABLE table [(column, column...)] AS subquery;

Creating a Table by Using a Subquery Name Null? Type EMPNO NOT NULL NUMBER(4) ENAME VARCHAR2(10) ANNSAL NUMBER HIREDATE DATE Name Null? Type EMPNO NOT NULL NUMBER(4) ENAME VARCHAR2(10) ANNSAL NUMBER HIREDATE DATE SQL> DESCRIBE dept30 SQL> CREATE TABLE dept30 2AS 3SELECT empno, ename, sal*12 ANNSAL, hiredate 4FROM emp 5WHERE deptno = 30; Table created. The slide example creates a table, DEPT30, that contains details of all the employees working in department 30. Notice that the data for the DEPT30 table is coming from the EMP table.

The ALTER TABLE Statement Use the ALTER TABLE statement to: Use the ALTER TABLE statement to: Add a new column Add a new column Modify an existing column Modify an existing column Define a default value for the new column Define a default value for the new column Use the ALTER TABLE statement to: Use the ALTER TABLE statement to: Add a new column Add a new column Modify an existing column Modify an existing column Define a default value for the new column Define a default value for the new column ALTER TABLE table ADD (column datatype [DEFAULT expr] [, column datatype]...); ALTER TABLE table MODIFY (column datatype [DEFAULT expr] [, column datatype]...);

Adding a Column DEPT30 EMPNO ENAME ANNSAL HIREDATE BLAKE MAY MARTIN SEP ALLEN FEB TURNER SEP “… add a new column into DEPT30 table …” DEPT30 EMPNO ENAME ANNSAL HIREDATE BLAKE MAY MARTIN SEP ALLEN FEB TURNER SEP JOB New column

Adding a Column You use the ADD clause to add columns. You use the ADD clause to add columns. EMPNO ENAME ANNSAL HIREDATE JOB BLAKE MAY MARTIN SEP ALLEN FEB TURNER SEP rows selected. EMPNO ENAME ANNSAL HIREDATE JOB BLAKE MAY MARTIN SEP ALLEN FEB TURNER SEP rows selected. SQL> ALTER TABLE dept30 2 ADD (job VARCHAR2(9)); Table altered. The new column becomes the last column.

Guidelines for Adding a Column You can add or modify columns, but you cannot drop them from a table. You cannot specify where the column is to appear. The new column becomes the last column. The example on the slide adds a column named JOB to the DEPT30 table. The JOB column becomes the last column in the table. Note: If a table already contains rows when a column is added, then the new column is initially null for all the rows.

Modifying a Column You can change a column ’ s datatype, size, and default value. You can change a column ’ s datatype, size, and default value. A change to the default value affects only subsequent insertions to the table. A change to the default value affects only subsequent insertions to the table. You can change a column ’ s datatype, size, and default value. You can change a column ’ s datatype, size, and default value. A change to the default value affects only subsequent insertions to the table. A change to the default value affects only subsequent insertions to the table. ALTER TABLEdept30 MODIFY(ename VARCHAR2(15)); Table altered.

Modifying a Column You can modify a column definition by using the ALTER TABLE statement with the MODIFY clause. Column modification can include changes to a column ’ s datatype, size, and default value. Guidelines Increase the width or precision of a numeric column. Decrease the width of a column if the column contains only null values or if the table has no rows. Change the datatype if the column contains null values. Convert a CHAR column to the VARCHAR2 datatype or convert a VARCHAR2 column to the CHAR datatype if the column contains null values or if you do not change the size. A change to the default value of a column affects only subsequent insertions to the table.

Dropping a Table All data and structure in the table is deleted. All data and structure in the table is deleted. Any pending transactions are committed. Any pending transactions are committed. All indexes are dropped. All indexes are dropped. You cannot roll back this statement. You cannot roll back this statement. All data and structure in the table is deleted. All data and structure in the table is deleted. Any pending transactions are committed. Any pending transactions are committed. All indexes are dropped. All indexes are dropped. You cannot roll back this statement. You cannot roll back this statement. SQL> DROP TABLE dept30; Table dropped.

Changing the Name of an Object To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. You must be the owner of the object. You must be the owner of the object. To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. You must be the owner of the object. You must be the owner of the object. SQL> RENAME dept TO department; Table renamed.

Truncating a Table The TRUNCATE TABLE statement: The TRUNCATE TABLE statement: Removes all rows from a table Removes all rows from a table Releases the storage space used by that table Releases the storage space used by that table You cannot roll back row removal when using TRUNCATE. You cannot roll back row removal when using TRUNCATE. Alternatively, you can remove rows by using the DELETE statement. Alternatively, you can remove rows by using the DELETE statement. The TRUNCATE TABLE statement: The TRUNCATE TABLE statement: Removes all rows from a table Removes all rows from a table Releases the storage space used by that table Releases the storage space used by that table You cannot roll back row removal when using TRUNCATE. You cannot roll back row removal when using TRUNCATE. Alternatively, you can remove rows by using the DELETE statement. Alternatively, you can remove rows by using the DELETE statement. SQL> TRUNCATE TABLE department; Table truncated.

Adding Comments to a Table You can add comments to a table or column by using the COMMENT statement. You can add comments to a table or column by using the COMMENT statement. Comments can be viewed through the data dictionary views. Comments can be viewed through the data dictionary views. ALL_COL_COMMENTS ALL_COL_COMMENTS USER_COL_COMMENTS USER_COL_COMMENTS ALL_TAB_COMMENTS ALL_TAB_COMMENTS USER_TAB_COMMENTS USER_TAB_COMMENTS You can add comments to a table or column by using the COMMENT statement. You can add comments to a table or column by using the COMMENT statement. Comments can be viewed through the data dictionary views. Comments can be viewed through the data dictionary views. ALL_COL_COMMENTS ALL_COL_COMMENTS USER_COL_COMMENTS USER_COL_COMMENTS ALL_TAB_COMMENTS ALL_TAB_COMMENTS USER_TAB_COMMENTS USER_TAB_COMMENTS SQL> COMMENT ON TABLE emp 2 IS 'Employee Information'; Comment created.

SummarySummary Statement Description CREATE TABLE Creates a table ALTER TABLE Modifies table structures DROP TABLE Removes the rows and table structure RENAME Changes the name of a table, view, sequence, or synonym TRUNCATE Removes all rows from a table and releases the storage space COMMENT Adds comments to a table or view

Practice Overview Creating new tables Creating new tables Creating a new table by using the CREATE TABLE AS syntax Creating a new table by using the CREATE TABLE AS syntax Modifying column definitions Modifying column definitions Verifying that the tables exist Verifying that the tables exist Adding comments to a tables Adding comments to a tables Dropping tables Dropping tables Altering tables Altering tables Creating new tables Creating new tables Creating a new table by using the CREATE TABLE AS syntax Creating a new table by using the CREATE TABLE AS syntax Modifying column definitions Modifying column definitions Verifying that the tables exist Verifying that the tables exist Adding comments to a tables Adding comments to a tables Dropping tables Dropping tables Altering tables Altering tables