本文概述
- 如何在表格中添加列
- 如何在现有表中添加多个列
- 如何修改表的列
- 如何修改表格的多列
- 如何删除表的列
- 如何重命名表的列
- 如何重命名表格
如何在表格中添加列句法:
ALTER TABLE table_name
ADD column_name column-definition;
【Oracle ALTER TABLE语句】例:
考虑已经存在的表客户。现在, 在表customers中添加新列customer_age。
ALTER TABLE customers
ADD customer_age varchar2(50);
现在, 将在客户表中添加一个新列” customer_age” 。
如何在现有表中添加多个列句法:
ALTER TABLE table_name
ADD (column_1 column-definition, column_2 column-definition, ...
column_n column_definition);
例子
ALTER TABLE customers
ADD (customer_type varchar2(50), customer_address varchar2(50));
Now, two columns customer_type and customer_address will be added in the table customers.
如何修改表的列句法:
ALTER TABLE table_name
MODIFY column_name column_type;
例:
ALTER TABLE customers
MODIFY customer_name varchar2(100) not null;
Now the column column_name in the customers table is modified
to varchar2 (100) and forced the column to not allow null values.
如何修改表格的多列句法:
ALTER TABLE table_name
MODIFY (column_1 column_type, column_2 column_type, ...
column_n column_type);
例:
ALTER TABLE customers
MODIFY (customer_name varchar2(100) not null, city varchar2(100));
This will modify both the customer_name and city columns in the table.
如何删除表的列句法:
ALTER TABLE table_name
DROP COLUMN column_name;
例:
ALTER TABLE customers
DROP COLUMN customer_name;
This will drop the customer_name column from the table.
如何重命名表的列句法:
ALTER TABLE table_name
RENAME COLUMN old_name to new_name;
例:
ALTER TABLE customers
RENAME COLUMN customer_name to cname;
This will rename the column customer_name into cname.
如何重命名表格句法:
ALTER TABLE table_name
RENAME TO new_table_name;
例:
ALTER TABLE customers
RENAME TO retailers;
This will rename the customer table into "retailers" table.
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