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UPDATE FROM CUSTOMER
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DROP FROM CUSTOMER
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DELETE FROM CUSTOMER
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REMOVE FROM CUSTOMER
EXPLANATION
SQL Delete Statement
The DELETE Statement is used to delete rows from a table.
Syntax of a SQL DELETE Statement
DELETE FROM table_name [WHERE condition];
- table_name -- the table name which has to be updated.
NOTE: The WHERE
clause in the sql delete command is optional and it identifies the
rows in the column that gets deleted. If you do not include the WHERE
clause all the rows in the table is deleted, so be careful while writing
a DELETE query without WHERE clause.
SQL DELETE Example
To delete an employee with id 100 from the employee table, the sql delete query would be like,
DELETE FROM employee WHERE id = 100;
To delete all the rows from the employee table, the query would be like,
DELETE FROM employee;
The SQL TRUNCATE command is used to delete all the rows from the table and free the space containing the table.
Syntax to TRUNCATE a table:
TRUNCATE TABLE table_name;
SQL TRUNCATE Statement Example
To delete all the rows from employee table, the query would be like,
TRUNCATE TABLE employee;
Difference between DELETE and TRUNCATE Statements:
DELETE Statement: This command deletes only the rows from the
table based on the condition given in the where clause or deletes all
the rows from the table if no condition is specified. But it does not
free the space containing the table.
TRUNCATE statement: This command is used to delete all the rows from the table and free the space containing the table.
The SQL DROP command is used to remove an object from the database.
If you drop a table, all the rows in the table is deleted and the table
structure is removed from the database. Once a table is dropped we
cannot get it back, so be careful while using DROP command. When a table
is dropped all the references to the table will not be valid.
Syntax to drop a sql table structure:
DROP TABLE table_name;
SQL DROP Statement Example
To drop the table employee, the query would be like
DROP TABLE employee;
Difference between DROP and TRUNCATE Statement:
If a table is dropped, all the relationships with other tables will no
longer be valid, the integrity constraints will be dropped, grant or
access privileges on the table will also be dropped, if you want use the
table again it has to be recreated with the integrity constraints,
access privileges and the relationships with other tables should be
established again. But, if a table is truncated, the table structure
remains the same, therefore any of the above problems will not exist.
