Creatingi a Tablele by Usingi a Subquery

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The ALTER TABLE Statement

Use the ALTER TABLE statement to:

•• Add a new columnl

•• Modifyify an existingi ti columnl

•• Definefi a defaultf lt valuel forf r thet new columnl

ALTER TABLE table

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Addingi a Columnl

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Addingi a Columnl

•• You use thet ADD clausel toto add columnsl ..

•• The new columnl becomes thet lastl t columnl ..

6 rows selected.

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Modifyingi i a Columnl

•• You can change a column'sl 's datatype,t t , size,i , and defaultf lt valuel ..

Table altered.

•• A change toto thet defaultf lt valuel affectsff ts onlyly subsequentt insertionsi rti toto thet tablet le..

10-16

Droppingi a Tablele

•• Allll datata and structuretr t re inin thet tablet le isis deletedl t ..

•• Any pendingi transactionstr ti arere committeditt ..

•• Allll indexesi arere droppedr ..

•• You cannott rollr ll back thist is statementt t t..

SQL> DROP TABLE dept30;

Table dropped.

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Changingi the Name of an Objectj

•• To change thet name off a table,t l , view,i , sequence,, orr synonym,, you executete thet RENAME statementt t t..

SQL> RENAME dept TO department;

Table renamed.

•• You mustt be thet ownerr off thet objectj t..

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Truncatingi a Tablele

•• The TRUNCATE TABLE statementt t t::

–Removes allll rowsr fromfr a tablet le

–Releasesl thet storaget r space used by thatt t tablet le

SQL> TRUNCATE TABLE department;

Table truncated.

•• Cannott rollr ll back rowr removalr l when usingi TRUNCATE

•• Alternatively,lt r ti l , remover rowsr by usingi thet

DELETE statementt t t

10-19

Addingi Comments to a Tablele

•• You can add commentsts toto a tablet le orr columnl by usingi thet COMMENT statementt t t..

SQL> COMMENT ON TABLE emp

2 IS 'Employee Information';

Comment created.

•• Commentsts can be viewedi throught r thet datata dictionaryi ti ry viewsi ..

–ALL_COL_COMMENTS

–USER_COL_COMMENTS

–ALL_TAB_COMMENTS

–USER_TAB_COMMENTS

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Summary

Statement Description

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