SQL Alter Table Column DEFAULT
Changing Table columns default value
- Most RDBMS systems allow you to change the structure of a table with the ALTER TABLE command.
- The syntax for changing or adding a DEFAULT value for a column is somewhat different for each RDBMS
- Below are guidelines for how to change the DEFAULT value for a column using some selected RDBMS;
Change the default value for a column:
ALTER TABLE table_name ALTER column_name SET DEFAULT value ;
ALTER TABLE TELEPHONES ALTER TELEPHONE_NUMBER SET DEFAULT 'NO PHONE';
ALTER TABLE table_name MODIFY column_name DEFAULT value ;
ALTER TABLE TELEPHONES MODIFY TELEPHONE_NUMBER DEFAULT 'NO PHONE';
ALTER TABLE table_name ADD CONSTRAINT constraint_name DEFAULT value FOR column_name;
- This is not a modify type, but ADDs a DEFAULT value to a column.
- We need to remove the constraint if it exists before this.
ALTER TABLE TELEPHONES DROP CONSTRAINT DF_TELEPHONE_NUMBER; /* we need to remove the constraint if it exists*/ ALTER TABLE TELEPHONES ADD CONSTRAINT DF_TELEPHONE_NUMBER DEFAULT 'NO PHONE' FOR TELEPHONE_NUMBER;
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