Oracle - SQL Table Basics - Altering/Adding Columns
Adding column
You can add new columns to an existing table. .
ALTER TABLE PHONE
MODIFY ( INACTIVE_DATE DATE )
/
Alter column
You can add modify an existing column
ALTER TABLE PERSON
MODIFY ( LASTNAME VARCHAR2(35) )
/
Considerations for altering a column
- Reducing precision (example, going from CHAR(20) to
CHAR(15)) can cause data truncation and should be avoided unless you
are absolutely sure their will be no impact to the data.
- Changing data types should typically be avoided.
There are exceptions to this. For example, changing a CHAR(20) to a
VARCHAR(20) on columns where the average storage length is 10 can
save disk space.
Alter columns - No Can Do
- You cannot directly alter a a column that is part
of the primary key
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