Note Candidate indexes (created by including the UNIQUE option, provided for ANSI compatibility in ALTER TABLE or CREATE TABLE) are not the same as indexes created with the UNIQUE option in the INDEX command. An index created with UNIQUE in the INDEX command allows duplicate index keys; candidat...
The SQL ALTER TABLE command is used to change the structure of an existing table. It helps to add or delete columns, create or destroy indexes, change the type of existing columns, or rename columns or the table itself. It can also be used to change the comment for the table and type ...
The ALTER TABLE command allows you to add, modify, or drop a column from an existing table. Adding column(s) to a table Syntax #1 To add a column to an existing table, the ALTER TABLE syntax is: ALTER TABLE table_name ADD column_name column-definition; For example: ALTER TABLE supplie...
We can also drop (remove) columns in a table using theALTER TABLEcommand with theDROPclause. For example, -- delete country column from Customers tableALTERTABLECustomersDROPCOLUMNcountry; Run Code Here, the SQL command removes thecountrycolumn from theCustomerstable. Rename a Table We can change...
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); ...
We can also remove multiple columns in a single Alter table command, but all columns should belong to a single table. This command removes [productFeedback] and [ProductlaunchDate] columns in a single command. 我们还可以在单个Alter table命令中删除多个列,但是所有列应属于一个表。 此命令在单个...
ALTER TABLE - ADD Column To add a column in a table, use the following syntax: ALTERTABLEtable_name ADDcolumn_name datatype; The following SQL adds an "Email" column to the "Customers" table: ExampleGet your own SQL Server ALTERTABLECustomers ...
The TableDirect // type is only for OLE DB. cmd.CommandType = commandType; cmd.Parameters.AddRange(parameters); conn.Open(); return cmd.ExecuteNonQuery(); } } } // Set the connection, command, and then execute the command and only return one value. public static Object ExecuteS...
postgres=# create table t_sex(id int,sex text) ; NOTICE: Replica identity is neededforshard table, pleaseaddto this table through"alter table"command. CREATE TABLE postgres=# create index t_sex_sex_idx on t_sex (sex); CREATE INDEX ...
The TableDirect // type is only for OLE DB. cmd.CommandType = commandType; cmd.Parameters.AddRange(parameters); conn.Open(); return cmd.ExecuteNonQuery(); } } } // Set the connection, command, and then execute the command and only return one value. public static Object ExecuteScalar(...