SQL Plus - Default Constraint

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Default Constraint

What is default constraint? How we you apply it?

Total Answers and Comments: 5

Last Update: June 15, 2009 Asked by: gagan87

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Submitted by: sreekanthjup

Default Contraint acts the same way as the other constraints like NOT NULL, UNIQUE, PRIMARY KEY............. do; they come into picture while data insertion is done into the table. It makes oracle insert a values automatically into table without being specified in the insert; for example:

CREATE TABLE TTEMP (NM VARCHAR2(10) DEFAULT 'Sreekanth', JOB VARCHAR2(10));

now we can skip from the NM column being filled:
INSERT INTO TTEMP VALUES (null,'sales'); or INSERT INTO TTEMP VALUES ('','sales');
in ordinary case without default constraint assigned.. NULL gets inserted but here 'Sreekanth' is inserted in each unspecified row.

Above answer was rated as good by the following members:
neelapu, himanshu_sapra, pakashraf

September 24, 2008 11:19:52

veerun14

Member Since: September 2008 Contribution: 4

RE: Default Constraint

By default the columns hold NULL if nothing is specified.
You can specify NOT NULL if you dont want NULL to be an attribute

UNIQUE and CHECK are other constraints

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September 26, 2008 15:01:34

hamsatharini

Member Since: September 2008 Contribution: 2

RE: Default Constraint

It specifies a default value for a new column or a new default for an existing column.
Oracle assigns this value to the column if a subsequent INSERT statement omits a value for the column.

A DEFAULT expression cannot contain references to other columns the pseudocolumns CURRVAL NEXTVAL LEVEL and ROWNUM or date constants that are not fully specified.

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January 19, 2009 10:20:38

sreekanthjup

Member Since: January 2009 Contribution: 1

RE: Default Constraint

Default Contraint acts the same way as the other constraints like NOT NULL UNIQUE PRIMARY KEY............. do; they come into picture while data insertion is done into the table. It makes oracle insert a values automatically into table without being specified in the insert; for example:

CREATE TABLE TTEMP (NM VARCHAR2(10) DEFAULT 'Sreekanth' JOB VARCHAR2(10));

now we can skip from the NM column being filled:
INSERT INTO TTEMP VALUES (null 'sales'); or INSERT INTO TTEMP VALUES ('' 'sales');
in ordinary case without default constraint assigned.. NULL gets inserted but here 'Sreekanth' is inserted in each unspecified row.

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April 19, 2009 07:27:35

rsmendu

Member Since: April 2009 Contribution: 1

RE: Default Constraint

When we create a constraint on a table and if that constraint is not named then Oracle gives a system default name to the constraint.

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June 15, 2009 08:17:46

gdurga

Member Since: June 2009 Contribution: 5

RE: Default Constraint

A coulumn can be given a default value by using DEFAULT option. This option prevents null values from entering the column if a row is inserted with out a value in to the table.
Ex:
.......
Hire_date DATE DEFAULT SYSDATE
.......

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