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03.12.01.18:38.Eric
03.11.27.20:45.Eric
                                                                              
-- For oracle
                                                                              
-- Describe a table's structure
DESC tablename
                                                                              
-- Alter table name
RENAME oldtablename TO newtablename
 
-- Add new column
ALTER TABLE atable ADD (newcolumn varchar(128))
 
-- Alter table column name
ALTER TABLE atable RENAME COLUMN oldcolumnname TO newcolumnname
                                                                             
-- Modify table column datatype
-- - Assume the table "atable" has a column "acolumn" which is
-- - VARCHAR2(10), the following command will change it to VA-
-- - CHAR(20)
ALTER TABLE atable MODIFY (acolumn VARCHAR2(20))

-- Add FK contraint
ALTER TABLE material
        add CONSTRAINT FK_MATERIAL_RELATIONS_DIFF
        FOREIGN KEY(difficultycode)
        REFERENCES difficulty (difficultycode)

-- Create a column equivalent to MySQL's AUTOINCREATMENT column
-- - Assume that we have a table "user" with two columns:
--      - USERID
--      - USERNAME
-- - First create a sequence
CREATE SEQUENCE seq_userid
        START WITH [n]

-- Then create the trigger to "auto increase" the userid
CREATE TRIGGER trg_user_insert
        BEFORE INSERT ON user
        FOR EACH ROW
BEGIN
        IF :new.userid IS NULL THEN
        SELECT seq_userid.NEXTVAL INTO :new.userid FROM DUAL;

        END IF;
END;
 
-- Set the Date column to get system date automatically
alter table atable modify (adatecolumn date default SYSDATE)


--
            Nothing is easy in fact
            Nothing is complicated indeed

                                    - 03.10.05.19:21.Eric
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