Copyright  Oracle Corporation, All rights reserved. 10 Creating and Managing Tables

10-2 Copyright  Oracle Corporation, All rights reserved. Objectives After completing this lesson, you should be able to do the following: Describe the main database objects Create tables Describe the datatypes that can be used when specifying column definition Alter table definitions Drop, rename, and truncate tables After completing this lesson, you should be able to do the following: Describe the main database objects Create tables Describe the datatypes that can be used when specifying column definition Alter table definitions Drop, rename, and truncate tables

10-3 Copyright  Oracle Corporation, All rights reserved. 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

10-4 Copyright  Oracle Corporation, All rights reserved. Naming Conventions Must begin with a letter Can be 1–30 characters long 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 be an Oracle Server reserved word Must begin with a letter Can be 1–30 characters long 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 be an Oracle Server reserved word

10-5 Copyright  Oracle Corporation, All rights reserved. The CREATE TABLE Statement You must have : – CREATE TABLE privilege – A storage area You specify: – Table name – Column name, column datatype, and column size You must have : – CREATE TABLE privilege – A storage area You specify: – Table name – Column name, column datatype, and column size CREATE [GLOBAL TEMPORARY] TABLE [schema.]table (column datatype [DEFAULT expr][,...]);

10-6 Copyright  Oracle Corporation, All rights reserved. Referencing Another User’s Tables 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. 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.

10-7 Copyright  Oracle Corporation, All rights reserved. The DEFAULT Option 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.

10-8 Copyright  Oracle Corporation, All rights reserved. Creating Tables SQL> CREATE TABLE dept 2(deptno NUMBER(2), 3 dname VARCHAR2(14), 4 loc VARCHAR2(13)); Table created. Create the table. Confirm table creation. SQL> DESCRIBE dept Name Null? Type DEPTNO NUMBER(2) DNAME VARCHAR2(14) LOC VARCHAR2(13)

10-9 Copyright  Oracle Corporation, All rights reserved. Tables in the Oracle Database User Tables – Collection of tables created and maintained by the user – Contain user information Data Dictionary – Collection of tables created and maintained by the Oracle server – Contain database information User Tables – Collection of tables created and maintained by the user – Contain user information Data Dictionary – Collection of tables created and maintained by the Oracle server – Contain database information

10-10 Copyright  Oracle Corporation, All rights reserved. Querying the Data Dictionary 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; Describe tables owned by the user.

10-11 Copyright  Oracle Corporation, All rights reserved. Datatypes 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

10-12 Copyright  Oracle Corporation, All rights reserved. Datatypes 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

10-13 Copyright  Oracle Corporation, All rights reserved. Creating a Table by Using a Subquery 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. Define columns with column names and default values. 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. Define columns with column names and default values. CREATE TABLE table [(column, column...)] AS subquery;

10-14 Copyright  Oracle Corporation, All rights reserved. SQL> CREATE TABLE dept30 2AS 3SELECT empno, ename, sal*12 ANNSAL, hiredate 4FROM emp 5WHERE deptno = 30; Table created. 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

10-15 Copyright  Oracle Corporation, All rights reserved. The ALTER TABLE Statement Use the ALTER TABLE statement to: Add a new column Modify an existing column Define a default value for the new column Use the ALTER TABLE statement to: Add a new column Modify an existing 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]...);

10-16 Copyright  Oracle Corporation, All rights reserved. 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

10-17 Copyright  Oracle Corporation, All rights reserved. Adding a Column 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.

10-18 Copyright  Oracle Corporation, All rights reserved. Modifying a Column You can change a column’s datatype, size, and default value. A change to the default value affects only subsequent insertions to the table. You can change a column’s datatype, size, and default value. A change to the default value affects only subsequent insertions to the table. SQL> ALTER TABLEdept30 2 MODIFY(ename VARCHAR2(15)); Table altered.

10-19 Copyright  Oracle Corporation, All rights reserved. Dropping a Column You use the DROP COLUMN clause drop columns you no longer need from the table. You use the DROP COLUMN clause drop columns you no longer need from the table. SQL> ALTER TABLEdept30 2 DROP COLUMN job ; Table altered.

10-20 Copyright  Oracle Corporation, All rights reserved. SET UNUSED Option You use the SET UNUSED option to mark one or more columns as unused. You use the DROP UNUSED COLUMNS option to remove the columns that are marked as UNUSED. You use the SET UNUSED option to mark one or more columns as unused. You use the DROP UNUSED COLUMNS option to remove the columns that are marked as UNUSED. ALTER TABLE table (column); ALTER TABLE table COLUMN column; ALTER TABLE table (column); ALTER TABLE table COLUMN column; OR ALTER TABLE table DROP UNUSED COLUMNS; ALTER TABLE table DROP UNUSED COLUMNS; SET UNUSED

10-21 Copyright  Oracle Corporation, All rights reserved. Dropping a Table All data and structure in the table is deleted. Any pending transactions are committed. All indexes are dropped. You cannot roll back this statement. All data and structure in the table is deleted. Any pending transactions are committed. All indexes are dropped. You cannot roll back this statement. SQL> DROP TABLE dept30; Table dropped.

10-22 Copyright  Oracle Corporation, All rights reserved. Changing the Name of an Object To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. You must be the owner of the object. To change the name of a table, view, sequence, or synonym, you execute the RENAME statement. You must be the owner of the object. SQL> RENAME dept TO department; Table renamed.

10-23 Copyright  Oracle Corporation, All rights reserved. Truncating a Table The TRUNCATE TABLE statement: – Removes all rows from a table – Releases the storage space used by that table You cannot roll back row removal when using TRUNCATE. Alternatively, you can remove rows by using the DELETE statement. The TRUNCATE TABLE statement: – Removes all rows from a table – Releases the storage space used by that table You cannot roll back row removal when using TRUNCATE. Alternatively, you can remove rows by using the DELETE statement. SQL> TRUNCATE TABLE department; Table truncated.

10-24 Copyright  Oracle Corporation, All rights reserved. Adding Comments to a Table You can add comments to a table or column by using the COMMENT statement. Comments can be viewed through the data dictionary views. – ALL_COL_COMMENTS – USER_COL_COMMENTS – ALL_TAB_COMMENTS – USER_TAB_COMMENTS You can add comments to a table or column by using the COMMENT statement. Comments can be viewed through the data dictionary views. – ALL_COL_COMMENTS – USER_COL_COMMENTS – ALL_TAB_COMMENTS – USER_TAB_COMMENTS SQL> COMMENT ON TABLE emp 2 IS 'Employee Information'; Comment created.

10-25 Copyright  Oracle Corporation, All rights reserved. Summary 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

10-26 Copyright  Oracle Corporation, All rights reserved. Practice Overview Creating new tables Creating a new table by using the CREATE TABLE AS syntax Modifying column definitions Verifying that the tables exist Adding comments to tables Dropping tables Altering tables Creating new tables Creating a new table by using the CREATE TABLE AS syntax Modifying column definitions Verifying that the tables exist Adding comments to tables Dropping tables Altering tables

10-27 Copyright  Oracle Corporation, All rights reserved.

10-28 Copyright  Oracle Corporation, All rights reserved.