Decrease the precision of a numeric column : Alter Table « Table « Oracle PL/SQL Tutorial

You can only decrease the precision of a numeric column if there are no rows in the table or the column contains null values.

SQL> -- create demo table
SQL> create table Employee(
  2    ID                 VARCHAR2(4 BYTE)         NOT NULL,
  3    First_Name         VARCHAR2(10 BYTE),
  4    Last_Name          VARCHAR2(10 BYTE),
  5    Start_Date         DATE,
  6    End_Date           DATE,
  7    Salary             Number(8,2),
  8    City               VARCHAR2(10 BYTE),
  9    Description        VARCHAR2(15 BYTE)
 10  )
 11  /

Table created.

SQL>
SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from Employee
  2  /

no rows selected

SQL>
SQL>
SQL> desc employee;
 Name                      Null?    Type
 --------------------------

 ID                        NOT NULL VARCHAR2(4)
 FIRST_NAME                         VARCHAR2(10)
 LAST_NAME                          VARCHAR2(10)
 START_DATE                         DATE
 END_DATE                           DATE
 SALARY                             NUMBER(8,2)
 CITY                               VARCHAR2(10)
 DESCRIPTION                        VARCHAR2(15)

SQL>
SQL> ALTER TABLE employee
  2  MODIFY salary NUMBER(2,2);

Table altered.

SQL>
SQL> desc employee;
 Name              Null?    Type
 ------------------

 ID                NOT NULL VARCHAR2(4)
 FIRST_NAME                 VARCHAR2(10)
 LAST_NAME                  VARCHAR2(10)
 START_DATE                 DATE
 END_DATE                   DATE
 SALARY                     NUMBER(2,2)
 CITY                       VARCHAR2(10)
 DESCRIPTION                VARCHAR2(15)

SQL>
SQL> select * from employee;

no rows selected

SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
  2  /

Table dropped.

SQL>
SQL>

6.3.Alter Table
	6.3.1.	Altering a Table
	6.3.2.	Some of the aspects of a column you can modify using ALTER TABLE
	6.3.3.	Adding a Column
	6.3.4.	ADD initially_created DATE DEFAULT SYSDATE NOT NULL;
	6.3.5.	Changing the Size of a Column
	6.3.6.	Decrease the length of a column
	6.3.7.	Changing the Precision of a Numeric Column
	6.3.8.	Decrease the precision of a numeric column
	6.3.9.	Changing the Data Type of a Column
	6.3.10.	Fill data into new added table column
	6.3.11.	Changing the Default Value of a Column
	6.3.12.	Alter table to add new constraint for new added column
	6.3.13.	ALTER TABLE to DISABLE a CONSTRAINT
	6.3.14.	Alter table to add primary key
	6.3.15.	Alter table to add primary key across more than one columns
	6.3.16.	Dropping a Column
	6.3.17.	New added columns are empty
	6.3.18.	Alter table to add unique with tablespace and storage setting
	6.3.19.	Alter table to add primary key with tablespace and storage setting
	6.3.20.	alter table nologging