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Oracle?????????

???????????????????????????Oracle????ALTER TABLE????????????????????ALTER TABLE????????????????????????????

1. ALTER TABLE???????

ALTER TABLE????????????????????????

1.1 ????

??????????????????

ALTER TABLE tablename ADD COLUMN new_column_name data_type [default_value] [NOT NULL];

• data_type?????????????VARCHAR(100)?
• [default_value]????????
• [NOT NULL]????????????

1.2 ???

???????????????????

ALTER TABLE tablename MODIFY COLUMN old_column_name new_column_name data_type [default_value] [NOT NULL];

???????????????????????????

1.3 ???

???????????????????

ALTER TABLE tablename DROP COLUMN old_column_name;

???????????????????????

1.4 ????

????????????????????

ALTER TABLE tablename RENAME COLUMN old_column_name TO new_column_name;

2. ???????

2.1 ????

??????????????????

ALTER TABLE tablename ADD CONSTRAINT constraint_name constraint_type (column_name);

• constraint_type????????PRIMARY KEY?UNIQUE??
• column_name????????

2.2 ????

????????????????????

ALTER TABLE tablename DROP CONSTRAINT constraint_name;

2.3 ??????

????????????????????

• ?????

ALTER TABLE tablename ENABLE PRIMARY KEY;

• ?????

ALTER TABLE tablename DISABLE PRIMARY KEY;

• ??????

ALTER TABLE tablename RENAME CONSTRAINT pk_id TO new_pk_id;

3. ???????

??????????????????????????????

3.1 ???

• ?????????????????
• ??????32????
• ????????_reserved_word????????????

3.2 ???

• ???????????????
• ??????32????
• ????????_reserved_word????????????

3.3 ????

• ??????????????????
• ???????64????
• ?????????_reserved_word????????????

4. ??SQL??

4.1 ????

SELECT emp.* AS emp_info
FROM emp
WHERE rownum <= 9;

• rownum?Oracle??????????????????

4.2 ????

SELECT *
FROM emp
WHERE rownum >= 7;

4.3 ??????

SELECT *
FROM emp
WHERE rownum >= 7
AND emp_id IN (SELECT emp_id FROM emp WHERE rownum <= 5);

5. ????

???????????????Oracle????????????????????????

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