copyright oracle corporation, 1999. all rights reserved. 10 creating and managing tables

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Copyright Oracle Corporation, 1999. All rights reserved. 10 10 Creating and Managing Tables

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Copyright Oracle Corporation, 1999. All rights reserved.

1010

Creating and Managing Tables

Creating and Managing Tables

10-2 Copyright Oracle Corporation, 1999. All rights reserved.

ObjectivesObjectives

After completing this lesson, you should After completing this lesson, you should be able to do the following: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 After completing this lesson, you should be able to do the following: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, 1999. All rights reserved.

Database ObjectsDatabase Objects

Object Description

Table Basic unit of storage; composed of rows

and columns

View Logically represents subsets of data from

one or more tables

Sequence Generates primary key values

Index Improves the performance of some queries

Synonym Gives alternative names to objects

10-4 Copyright Oracle Corporation, 1999. All rights reserved.

Naming ConventionsNaming 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, 1999. All rights reserved.

The CREATE TABLE StatementThe 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, 1999. All rights reserved.

Referencing Another User’s Tables

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, 1999. All rights reserved.

The DEFAULT OptionThe 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.

10-8 Copyright Oracle Corporation, 1999. All rights reserved.

Creating TablesCreating Tables

SQL> CREATE TABLE dept 2 (deptno NUMBER(2), 3 dname VARCHAR2(14), 4 loc VARCHAR2(13));Table created.Table created.

• Create the table.• Create the table.

• Confirm table creation.• Confirm table creation. SQL> DESCRIBE dept

Name Null? Type --------------------------- -------- --------- DEPTNO NUMBER(2) DNAME VARCHAR2(14) LOC VARCHAR2(13)

10-9 Copyright Oracle Corporation, 1999. All rights reserved.

Tables in the Oracle DatabaseTables 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, 1999. All rights reserved.

Querying the Data DictionaryQuerying the Data Dictionary

• View distinct object types owned by the user.

• View distinct object types owned by the user.

• View tables, views, synonyms, and sequences owned by the user.

• View tables, views, synonyms, and sequences owned by the user.

SQL> SELECT * 2 FROM user_tables;

SQL> SELECT DISTINCT object_type 2 FROM user_objects;

SQL> SELECT * 2 FROM user_catalog;

• Describe tables owned by the user.• Describe tables owned by the user.

10-11 Copyright Oracle Corporation, 1999. All rights reserved.

DatatypesDatatypes

Datatype Description

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

CLOB Single-byte character data up to 4 gigabytes

RAW and LONG RAW Raw binary data

BLOB Binary data up to 4 gigabytes

BFILE Binary data stored in an external file; up to 4 gigabytes

10-13 Copyright Oracle Corporation, 1999. All rights reserved.

Creating a Table by Using a Subquery

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 anddefault 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 anddefault values.

CREATE TABLE table [(column, column...)]AS subquery;

10-14 Copyright Oracle Corporation, 1999. All rights reserved.

SQL> CREATE TABLE dept30 2 AS 3 SELECT empno, ename, sal*12 ANNSAL, hiredate 4 FROM emp 5 WHERE deptno = 30;Table created.Table created.

Creating a Table by Using a 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

10-15 Copyright Oracle Corporation, 1999. All rights reserved.

The ALTER TABLE StatementThe ALTER TABLE Statement

Use the ALTER TABLE statement to: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:Use the ALTER TABLE statement to:

• Add a new column

• Modify an existing column

• Define a default value for the new column

ALTER TABLE tableADD (column datatype [DEFAULT expr]

[, column datatype]...);

ALTER TABLE tableMODIFY (column datatype [DEFAULT expr]

[, column datatype]...);

10-16 Copyright Oracle Corporation, 1999. All rights reserved.

Adding a ColumnAdding a Column

DEPT30DEPT30 EMPNO ENAME ANNSAL HIREDATE ------ ---------- -------- 7698 BLAKE 34200 01-MAY-81 7654 MARTIN 15000 28-SEP-81 7499 ALLEN 19200 20-FEB-81 7844 TURNER 18000 08-SEP-81...

“…“…add a add a newnewcolumn column intointoDEPT30 DEPT30 table…”table…”

DEPT30DEPT30 EMPNO ENAME ANNSAL HIREDATE ------ ---------- -------- 7698 BLAKE 34200 01-MAY-81 7654 MARTIN 15000 28-SEP-81 7499 ALLEN 19200 20-FEB-81 7844 TURNER 18000 08-SEP-81...

JOB

JOB

New columnNew column

10-17 Copyright Oracle Corporation, 1999. All rights reserved.

Adding a ColumnAdding a Column

• You use the ADD clause to add columns.• You use the ADD clause to add columns.

EMPNO ENAME ANNSAL HIREDATE JOB--------- ---------- --------- --------- ---- 7698 BLAKE 34200 01-MAY-81 7654 MARTIN 15000 28-SEP-81 7499 ALLEN 19200 20-FEB-81 7844 TURNER 18000 08-SEP-81...6 rows selected.

EMPNO ENAME ANNSAL HIREDATE JOB--------- ---------- --------- --------- ---- 7698 BLAKE 34200 01-MAY-81 7654 MARTIN 15000 28-SEP-81 7499 ALLEN 19200 20-FEB-81 7844 TURNER 18000 08-SEP-81...6 rows selected.

SQL> ALTER TABLE dept30 2 ADD (job VARCHAR2(9));Table altered.Table altered.

• The new column becomes the last column.• The new column becomes the last column.

10-18 Copyright Oracle Corporation, 1999. All rights reserved.

Modifying a ColumnModifying 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 TABLE dept30 2 MODIFY (ename VARCHAR2(15));Table altered.Table altered.

10-19 Copyright Oracle Corporation, 1999. All rights reserved.

Dropping a ColumnDropping a Column

You use the DROP COLUMN clause dropcolumns you no longer need from thetable.

You use the DROP COLUMN clause dropcolumns you no longer need from thetable.

SQL> ALTER TABLE dept30 2 DROP COLUMN job ;Table altered.Table altered.

10-20 Copyright Oracle Corporation, 1999. All rights reserved.

SET UNUSED OptionSET 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 tableDROP UNUSED COLUMNS;

ALTER TABLE tableDROP UNUSED COLUMNS;

SET UNUSED

SET UNUSED

10-21 Copyright Oracle Corporation, 1999. All rights reserved.

Dropping a TableDropping 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.Table dropped.

10-22 Copyright Oracle Corporation, 1999. All rights reserved.

Changing the Name of an ObjectChanging 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.Table renamed.

10-23 Copyright Oracle Corporation, 1999. All rights reserved.

Truncating a TableTruncating 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.Table truncated.

10-24 Copyright Oracle Corporation, 1999. All rights reserved.

Adding Comments to a TableAdding 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.Comment created.

10-25 Copyright Oracle Corporation, 1999. All rights reserved.

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

10-26 Copyright Oracle Corporation, 1999. All rights reserved.

Practice OverviewPractice 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