SQL ALTER TABLE 语句 ALTER TABLE 语句用于添加、删除或修改现有表中的列。 ALTER TABLE 语句还用于添加和删除现有表上的各种约束。 ALTER TABLE - 添加列 要在表中添加列,请使用以下语法: ALTERTABLEtable_name ADDcolumn_name datatype; 以下SQL将"Email"列添加到"Customers"表中: ...
ALTERTABLEtable_name ADDcolumn_name datatype; The following SQL adds an "Email" column to the "Customers" table: ExampleGet your own SQL Server ALTERTABLECustomers ADDEmail varchar(255); ALTER TABLE - DROP COLUMN To delete a column in a table, use the following syntax (notice that some da...
The ALTER TABLE command adds, deletes, or modifies columns in a table.The ALTER TABLE command also adds and deletes various constraints in a table.The following SQL adds an "Email" column to the "Customers" table:ExampleGet your own SQL Server ALTER TABLE CustomersADD Email varchar(255); ...
ALTERTABLECustomers ADDEmail varchar(255); The following SQL deletes the "Email" column from the "Customers" table: Example ALTERTABLECustomers DROPCOLUMNEmail; DROP TABLE TheDROP TABLEcommand deletes a table in the database. The following SQL deletes the table "Shippers": ...