[Oracle] [命令] 修改字段类型

 
Oracle provides "alter table" syntax to modify data columns in-place in this form:

alter table
   table_name
modify
   column_name  datatype;

If you are brave you can use a single "alter table" syntax to modify multiple columns:

alter table
   table_name
modify
   (
   column1_name  column1_datatype,
   column2_name  column2_datatype,
   column3_name  column3_datatype,
   column4_name  column4_datatype
   );

Here are some examples of Oracle "alter table" syntax to modify data columns and note that you can add constraints like NOT NULL:

ALTER TABLE
   customer
MODIFY
   (
   cust_name varchar2(100) not null,
   cust_hair_color  varchar2(20)
   )
;

ALTER TABLE t_yms_template  MODIFY ( REQST_START_MOTH null);

We can also use Oracle "alter table" syntax in dynamic PL/SQL to modify data columns

BEGIN
SQL_STRING := 'ALTER TABLE '||:TABLE_NAME||' MODIFY '||:COLUMN_NAME||' VARCHAR2(100';
 . . .
END;