10
Creating and Managing
Tables
Objectivesj i
After completing this lesson, you should be able to do the following:
•• Describeri thet mainin databaset objectsj ts
•• Creater te tablest l
•• Describeri thet datatypest t thatt t can be used when specifyingif i columnl definitionfi iti
•• Alterlt r tablet le definitionsfi iti
•• Drop,r , rename,r , and truncatetr te tablest l
10-2
Database Objectsj
Object |
Description |
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Table |
Basic unit of storage; composed of rows |
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and columns |
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View |
Logically represents subsets of data from |
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one or more tables |
Sequence |
Generates primary key values |
Index |
Improves the performance of some queries |
Synonym |
Gives alternative names to objects |
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10-3
Namingi Conventionsi
•• Mustt beginin withith a letterl tt r
•• Can be 1–30 charactersr t rs longl
•• Mustt containt in onlyly A–Z,, a–z,, 0–9,, _,, $,, and #
•• Mustt nott duplicateli te thet name off anothert r objectj t owned by thet same userr
•• Mustt nott be an Oracler le Serverr r reservedr r wordrd
10-4
The CREATE TABLE Statement
•• You mustt have ::
–CREATE TABLE privilegeri il
–A storaget r arear
CREATE TABLE [schema.]table
(column datatype [DEFAULT expr]);
•• You specifyify::
–Tablele name
–Columnl name,, columnl datatype,t t , and columnl sizei
10-5
Referencingi Another User’s’s
Tablesl
•• Tablesl belongingl i toto othert r usersrs arere nott inin thet user’sr’s schema..
•• You shouldld use thet owner’sr’s name as a prefixr fix toto thet tablet le..
10-6
The DEFAULT Optioni
•• Specifyify a defaultf lt valuel forf r a columnl duringri an inserti rt..
… hiredate DATE DEFAULT SYSDATE, …
•• Legall valuesl arere literallit r l value,l , expression,r i , orr SQL functionf ti ..
•• IllegalIll l valuesl arere anothert r column’sl ’s name orr pseudocolumnl ..
•• The defaultf lt datatypet t mustt matcht thet columnl datatypet t ..
10-7
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Creatingi Tablesl |
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•• Create the table. |
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te t t |
le. |
SQL> CREATE TABLE dept |
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2 |
(deptno |
NUMBER(2), |
3 |
dname |
VARCHAR2(14), |
4 |
loc |
VARCHAR2(13)); |
Table created.
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•• Confirm table creation. |
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firm t le r |
ti . |
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SQL> DESCRIBE dept |
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Name |
Null? |
Type |
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--------------------------- |
-------- |
--------- |
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DEPTNO |
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NUMBER(2) |
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DNAME |
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VARCHAR2(14) |
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LOC |
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VARCHAR2(13) |
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10-8
Queryingi the Data Dictionaryi i
•• Describeri tablest l owned by thet userr..
SQL> SELECT * |
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2 |
FROM |
user_tables; |
•• Viewi distincti ti t objectj t typest owned by thet userr..
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SQL> SELECT |
DISTINCT object_type |
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2 |
FROM |
user_objects; |
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•• Viewi tables,t l , views,i , synonyms,, and sequences owned by thet userr..
SQL> SELECT *
2FROM user_catalog;
10-9
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Datatypes |
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Datatype |
Description |
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VARCHAR2(size)Variable-length character data |
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CHAR(size) |
Fixed-length character data |
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NUMBER(p,s) Variable-length numeric data |
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DATE |
Date and time values |
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LONG |
Variable-length character data |
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up to 2 gigabytes |
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CLOB |
Single-byte character data up to 4 |
gigabytes |
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RAW and LONG RAW Raw binary data |
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BLOB |
Binary data up to 4 gigabytes |
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BFILE |
Binary data stored in an external |
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file; up to 4 gigabytes
10-10
Creatingi a Tablele by Usingi a Subquery
•• Creater te a tablet le and inserti rt rowsr by combiningi i thet CREATE TABLE statementt t t and AS subqueryry optionti ..
CREATE TABLE table
[column(, column...)]
AS subquery;
•• Matcht thet numberr off specifiedifi columnsl toto thet numberr off subqueryry columnsl ..
•• Definefi columnsl withith columnl names and defaultf lt valuesl ..
10-11