<< Dropping constraints | CREATE statements >>

New column with a column-level constraint

<< Dropping constraints | CREATE statements >>

Derby Reference Manual

Examples

-- Add a new column with a column-level constraint
-- to an existing table
-- An exception will be thrown if the table
-- contains any rows
-- since the newcol will be initialized to NULL
-- in all existing rows in the table
ALTER TABLE CITIES ADD COLUMN REGION VARCHAR(26)
CONSTRAINT NEW_CONSTRAINT CHECK (REGION IS NOT NULL);

-- Add a new unique constraint to an existing table
-- An exception will be thrown if duplicate keys are found
ALTER TABLE SAMP.DEPARTMENT
ADD CONSTRAINT NEW_UNIQUE UNIQUE (DEPTNO);

-- add a new foreign key constraint to the
-- Cities table. Each row in Cities is checked
-- to make sure it satisfied the constraints.
-- if any rows don't satisfy the constraint, the
-- constraint is not added
ALTER TABLE CITIES ADD CONSTRAINT COUNTRY_FK
Foreign Key (COUNTRY) REFERENCES COUNTRIES (COUNTRY);

-- Add a primary key constraint to a table
-- First, create a new table
CREATE TABLE ACTIVITIES (CITY_ID INT NOT NULL,
SEASON CHAR(2), ACTIVITY VARCHAR(32) NOT NULL);
-- You will not be able to add this constraint if the
-- columns you are including in the primary key have
-- null data or duplicate values.
ALTER TABLE Activities ADD PRIMARY KEY (city_id, activity);

-- Drop the city_id column if there are no dependent objects:
ALTER TABLE Cities DROP COLUMN city_id RESTRICT;
-- Drop the city_id column, also dropping all dependent objects:
ALTER TABLE Cities DROP COLUMN city_id CASCADE;

-- Drop a primary key constraint from the CITIES table

ALTER TABLE Cities DROP CONSTRAINT Cities_PK;
-- Drop a foreign key constraint from the CITIES table
ALTER TABLE Cities DROP CONSTRAINT COUNTRIES_FK;
-- add a DEPTNO column with a default value of 1
ALTER TABLE SAMP.EMP_ACT ADD COLUMN DEPTNO INT DEFAULT 1;
-- increase the width of a VARCHAR column
ALTER TABLE SAMP.EMP_PHOTO ALTER PHOTO_FORMAT SET DATA TYPE VARCHAR(30);
-- change the lock granularity of a table
ALTER TABLE SAMP.SALES LOCKSIZE TABLE;

-- Remove the NOT NULL constraint from the MANAGER column
ALTER TABLE Employees ALTER COLUMN Manager NULL;
-- Add the NOT NULL constraint to the SSN column
ALTER TABLE Employees ALTER COLUMN ssn NOT NULL;

-- Change the default value for the SALARY column
ALTER TABLE Employees ALTER COLUMN Salary DEFAULT 1000.0
ALTER TABLE Employees ALTER COLUMN Salary DROP DEFAULT

Results

An ALTER TABLE statement causes all statements that are dependent on the table
being altered to be recompiled before their next execution. ALTER TABLE is not allowed
if there are any open cursors that reference the table being altered.

CALL (PROCEDURE) statement