Oracle__约束
约束查询：
Select constraint_name, search_condition From USER_CONSTRAINTSWhere table_name = 'your table name';
Alter Table your_table Drop Constraint constraint_name;constraint_name是上一条语句查出来的
--非空Alter Table your_table Modify field_name NOT NULL;--主键Alter Table your_table Add Constraint tb_pk Primary Key( field_name );--外键Alter Table your_table Add Constraint tb_fk Foreign Key( field_name ) References your_table2(field_name);
修改字段的默认值Alter Table tbl_name modify col_name default(col_value);
