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This Oracle tutorial explains how to use the OracleALTER table statementto add a column,modify a column,drop a column,rename a column or rename a table (with Syntax,examples and practice exercises).
The Oracle ALTER table statement is used to add,modify,or drop/delete columns in a table. The Oracle ALTER table statement is also used to rename a table.
To ADD A ColUMN in a table,the Oracle ALTER table Syntax is:
ALTER table table_name ADD column_name column-deFinition;
Let's look at an example that shows how to add a column in an Oracle table using the ALTER table statement.
For example:
ALTER table customers ADD customer_name varchar2(45);
This Oracle ALTER table example will add a column calledcustomer_nameto thecustomerstable.
To ADD MulTIPLE ColUMNS to an existing table,246)">ALTER table table_name ADD (column_1 column-deFinition,column_2 column-deFinition,... column_n column_deFinition);
Let's look at an example that shows how to add multiple columns in an Oracle table using the ALTER table statement.
For example:
ALTER table customers ADD (customer_name varchar2(45),city varchar2(40));
This Oracle ALTER table example will add two columns,customer_nameas a varchar2(45) fIEld andcityas a varchar2(40) fIEld to thecustomerstable.
To MODIFY A ColUMN in an existing table,246)">ALTER table table_name MODIFY column_name column_type;
Let's look at an example that shows how to modify a column in an Oracle table using the ALTER table statement.
For example:
ALTER table customers MODIFY customer_name varchar2(100) not null;
This Oracle ALTER table example will modify the column calledcustomer_nameto be a data type of varchar2(100) and force the column to not allow null values.
To MODIFY MulTIPLE ColUMNS in an existing table,246)">ALTER table table_name MODIFY (column_1 column_type,column_2 column_type,... column_n column_type);
Let's look at an example that shows how to modify multiple columns in an Oracle table using the ALTER table statement.
For example:
ALTER table customers MODIFY (customer_name varchar2(100) not null,city varchar2(75));
This Oracle ALTER table example will modify both thecustomer_nameandcitycolumns.
To DROP A ColUMN in an existing table,246)">ALTER table table_name DROP ColUMN column_name;
Let's look at an example that shows how to drop a column in an Oracle table using the ALTER table statement.
For example:
ALTER table customers DROP ColUMN customer_name;
This Oracle ALTER table example will drop the column calledcustomer_namefrom the table calledcustomers.
Starting in Oracle 9i Release 2,you can Now rename a column.
To REname A ColUMN in an existing table,246)">ALTER table table_name REname ColUMN old_name to new_name;
Let's look at an example that shows how to rename a column in an Oracle table using the ALTER table statement.
For example:
ALTER table customers REname ColUMN customer_name to cname;
This Oracle ALTER table example will rename the column calledcustomer_nametocname.
To REname A table,246)">ALTER table table_name REname TO new_table_name;
Let's look at an example that shows how to rename a table in Oracle using the ALTER table statement.
For example:
ALTER table customers REname TO contacts;
This Oracle ALTER table example will rename thecustomerstable tocontacts.
Based on thedepartmentstable below,rename thedepartmentstable todepts.
CREATE table departments ( department_ID number(10) not null,department_name varchar2(50) not null,CONSTRAINT departments_pk PRIMARY KEY (department_ID) );
The following Oracle ALTER table statement would rename thedepartmentstable todepts:
ALTER table departments REname TO depts;
Based on theemployeestable below,add a column calledbonusthat is a number(6) datatype.
CREATE table employees ( employee_number number(10) not null,employee_name varchar2(50) not null,department_ID number(10),CONSTRAINT employees_pk PRIMARY KEY (employee_number) );
The following Oracle ALTER table statement would add abonuscolumn to theemployeestable:
ALTER table employees ADD bonus number(6);
Based on thecustomerstable below,add two columns - one column calledcontact_namethat is a varchar2(50) datatype and one column calledlast_contactedthat is a date datatype.
CREATE table customers ( customer_ID number(10) not null,customer_name varchar2(50) not null,address varchar2(50),city varchar2(50),state varchar2(25),zip_code varchar2(10),CONSTRAINT customers_pk PRIMARY KEY (customer_ID) );
The following Oracle ALTER table statement would add thecontact_nameandlast_contactedcolumns to thecustomerstable:
ALTER table customers ADD (contact_name varchar2(50),last_contacted date);
Based on theemployeestable below,change theemployee_namecolumn to a varchar2(75) datatype.
Solution for Practice Exercise #4:The following Oracle ALTER table statement would change the datatype for theemployee_namecolumn to varchar2(75):
ALTER table employees MODIFY employee_name varchar2(75);Practice Exercise #5:
Based on thecustomerstable below,change thecustomer_namecolumn to NOT allow null values and change thestatecolumn to a varchar2(2) datatype.
Solution for Practice Exercise #5:The following Oracle ALTER table statement would modify thecustomer_nameandstatecolumns accordingly in thecustomerstable:
ALTER table customers MODIFY (customer_name varchar2(50) not null,state varchar2(2));Practice Exercise #6:
Based on theemployeestable below,drop thesalarycolumn.
Solution for Practice Exercise #6:The following Oracle ALTER table statement would drop thesalarycolumn from theemployeestable:
ALTER table employees DROP ColUMN salary;Practice Exercise #7:
Based on thedepartmentstable below,rename thedepartment_namecolumn todept_name.
Solution for Practice Exercise #7:The following Oracle ALTER table statement would rename thedepartment_namecolumn todept_namein thedepartmentstable:
ALTER table departments REname ColUMN department_name to dept_name;from https://www.techonthenet.com/oracle/index.PHP
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