The following SQL statement updates the first customer (CustomerID = 1) with a new contact person and a new city.
UPDATE Customers SET ContactName = 'Alfred Schmidt', City= 'Frankfurt' WHERE CustomerID = 1;
UPDATE Multiple Records
It is the WHERE clause that determines how many records that will be updated.
The following SQL statement will update the contactname to “Juan” for all records where country is “Mexico”:
UPDATE Customers SET ContactName='Juan' WHERE Country='Mexico';
Be careful when updating records. If you omit the WHERE clause, ALL records will be updated!
UPDATE Customers SET ContactName='Juan';
ALTER TABLE – ADD Column
To add a column in a table, use the following syntax:
ALTER TABLE table_name ADD column_name datatype;
ALTER TABLE – ALTER/MODIFY COLUMN
To change the data type of a column in a table, use the following syntax:
SQL Server / MS Access:
ALTER TABLE table_name ALTER COLUMN column_name datatype;
DELETE COLUMN/TABLE TABLE
DELETE FROM Customers WHERE CustomerName='Alfreds Futterkiste'; DELETE FROM table_name WHERE condition;
Delete All Records
DELETE * FROM table_name;
ALTER TABLE – DROP COLUMN
To delete a column in a table, use the following syntax (notice that some database systems don’t allow deleting a column):
ALTER TABLE table_name DROP COLUMN column_name;