Oracle about defining constraints/modifying table structures/modifying constraints

There are 5 types of---Constraints: PRIMARY key foreign key unique non-NULL check 5 class constraints

Column-level constraints and table-level constraints in Oracle

Column-level constraints: Columns are then added to the constraint when the table is created

For example:

CREATE TABLE Table11 (Stuno number (2) constraint TABLE_PK primary key,tname varchar2 (5) unique--unique constraint)

The above two fields are the constraints written directly above the columns: Optional [constraint TABLE_PK] primary key,

Table-level constraints:

For example:

--table-level constraint CREATE TABLE Table22 (Idno number (2), Tname varchar2 (5) unique,--UNIQUE constraint price number (5,2) check (price>100),-- Check constraint Stuno number (2),    --below the table-level constraint is the constraint TB_2_PK primary key (Idno) under all the shoes columns, constraint TB_2_FK foreign key ( Stuno) references Table11 (Stuno))

Add a constraint called table-level constraint below all fields

----------------Modifying a table

ALTER TABLE TABLE22 drop [column name,,,]--delete column ALTER TABLE TABLE22 add column name type [default value]--add column ALTER TABLE table22 modify column name Type [default]--Modify Column

--------Adding table-level constraints

ALTER TABLE TABLENAMEADD constraint TABLE_PK primary key (ID);--Add primary key ALTER TABLE Tablenamedrop table_pk;--Delete primary key

------To modify a constraint on a column

ALTER TABLE tablename Modify column name constraint Notnull not null;--add non-null constraint ALTER TABLE tablename modify column name constraint Check2 CHEC K (column name >1200);--check constraint

-----To remove a constraint for a column

ALTER TABLE tname  DROP constraint constraint name;--delete ALTER TABLE Tname  modify column name by constraint name null;--Delete non-null constraint

　　

　　

　　

　　

Oracle about defining constraints/modifying table structures/modifying constraints