修改字段的语法:alter table tablename modify (column datatype [default value][null/not null],….); 删除字段的语法:alter table tablename drop (column); 添加、修改、删除多列的话,用逗号隔开。 使用alter table 来增加、删除和修改一个列的例子。 创建表结构: create table test1 (id varchar2(20) ...
create table liu(a varchar2 ( 20 ),b number ( 2 )) alter table liu rename to jin rename jin to cai alter table cai add c varchar2 ( 30 ) alter table cai add (d varchar2 ( 30 ),e number ( 4 )) alter table cai rename column e to f alter table cai modify d varchar ( 40...
To use an object type in a column definition when modifying a table, either that object must belong to the same schema as the table being altered, or you must have either theEXECUTEANYTYPEsystem privilege or theEXECUTEschema object privilege for the object type. See Also: CREATE INDEXfor inf...
使用CREATE TABLE命令创建表时,可以为每列指定默认值。即当向表中插入数据,且不指定该列的值时,系统会自动地采用设定的默认值。指定默认值是通过DEFAULT关键字来实现的,其语法如下:<column name> <data type> DEFAULT <default value> 在DEFAULT关键字后面指定该列的默认值,无论<default value>使用什么类型的值,...
reftable [ ( refcolumn ) ] [ MATCH FULL | MATCH PARTIAL | MATCH SIMPLE ] [ ON DELETE referential_action ] [ ON UPDATE referential_action ] } [ DEFERRABLE | NOT DEFERRABLE ] [ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] 而table_constraint是: [ CONSTRAINT constraint_name ] { CHECK ( ...
If you want to add multiple columns to a table in Oracle, you can use multiple ADD clauses in the ALTER TABLE statement. ALTER TABLE table_name ADD column1_name datatype1 [DEFAULT default_value1] [NULL|NOT NULL] [CONSTRAINT constraint1_name] [column1_constraint_clause], ...
Summary: in this tutorial, you will learn how to use the Oracle ALTER TABLE ADD column statement to add one or more columns to a table. To add a new column to a table, you use the ALTER TABLE statement as follows: ALTER TABLE table_name ADD column_name data_type constraint; Code lan...
ALTER TABLE用于更改一个现有表的定义。 简介 ALTER TABLE更改一个现有表的定义。下文描述了几种形式。注意每一种形式所要求的锁级别可能不同。如果没有明确说明,将会获得一个ACCESS EXCLUSIVE锁。当给出多个子命令时,获得的锁将是子命令所要求的最严格的那一个。 ADD COLUMN [ IF NOT EXISTS ]这种形式向该表增...
The SQL92 standards specify that security administrators should be able to require that users have SELECT privilege on a table when executing an UPDATE or DELETE statement that references table column values in a WHERE or SET clause. SQL92_SECURITY lets you specify whether users must have been gra...
table_options signifies table options of the kind that can be used in the CREATE TABLE statement, such as ENGINE, AUTO_INCREMENT, AVG_ROW_LENGTH, MAX_ROWS, ROW_FORMAT, or TABLESPACE. For descriptions of all table options, see Section 15.1.20, “CREATE TABLE Statement”. However, ALTER ...