Add Column SQL
In this post Add Column SQL
, we will have an idea about alter table command of sql. After reading this post Add
Column SQL, readers will be able to add columns to existing tables as
well as they will be able to alter the existing columns of the tables. Sometimes after the creation of a table, need of addition of a new column exists, in that case Alter table command is helpful.
 |
| Add Column SQL |
Before we discuss add
column SQL , lets us see why to add columns in an existing table. Sometimes
while deciding columns of a table, we forget to include a particular field, in
that case we can add new columns to the existing tables.
In programming , some
times need of a new columns in existing tables arises at a later stage.
In SQL, we can add a new
column in an existing table as well as we can change the specifications of the
existing columns.
Suppose you have a table
named employee in database as given below-
Ecode
|
Ename
|
Ecity
|
After creating this
table, need of a new column named zip code arises. You can add this new column
using alter table command.
Add Column SQL
Add column SQL requires knowledge of alter table command of sql. Using alter table
command, one can add new columns as well as can change the specifications of
the existing columns. You can change the data types of the existing columns,
one can change the field width of the existing columns.
 |
| Add Column SQL |
Alter Table Command
A table in SQL can
be altered by using alter table command. By using alter
table command , we can add new columns to an existing table. We
can also change specification of the existing columns of a table using Alter
Table command.
Whenever you will try to add column
in sql, you have to take care of data.
Suppose you have a table named
employee as given below –
Ecode
|
Ename
|
Ecity
|
E001
|
JOE
|
FLORDA
|
E002
|
JIM
|
SYDNEY
|
If you add a new column named zip code in the above table,
structure of the above table will be like this-
Ecode
|
Ename
|
Ecity
|
Zip code
|
E001
|
JOE
|
FLORDA
|
|
E002
|
JIM
|
SYDNEY
|
|
Here you can see Zip code column is having no values, and
then what will the values of Zip code in case of these two entered records.
In that case you have to use update command to add values to these two already entered records.
How to Add Column in sql table using Alter Table command
To add new columns in an existing
table, we can use add option of alter table command.
The general syntax of
alter table command with add option is given below:
Alter table <table-name> add( new column specification);
Suppose we want to add zipcode
column in employee table.
SQL>Alter
table employee add(zipcode number(10));
This will add a new column zipcode
to employee table.
Modifying existing columns of a table
To modify specification of existing
columns of a table ,we can use modify option of alter
table command.
The general syntax for
modifying existing columns is given below
Alter
table <table-name> modify( column new_specification);
Suppose we wants to chamge filed
width of ecode column from 4 to 6.
SQL>Alter
Table employee modify( ecode char(6));
Note: Be careful
while changing column specifications, this is because when you to change
the data type of an existing column, if the table is having data that time,
there may be some issues of data type mismatch. Also in case of column width
alteration, if you try to reduce the width of an existing column , if that
column is having values, in that case truncation of data may happen.
Summary
Hope this post add column sql , is informative for
you.Using alter table command, one can add column in sql as well as can alter the existing columns.
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