The DROP TABLE command deletes a table in the database.
The following SQL deletes the table “Shippers”:
DROP TABLE Shippers;
Note: Be careful before deleting a table. Deleting a table results in loss of all information stored in the table!
The DROP INDEX command is used to delete an index in a table.
MS Access:
DROP INDEX index_name ON table_name;
SQL Server:
DROP INDEX table_name.index_name;
The DROP DEFAULT command is used to delete a DEFAULT constraint.
To drop a DEFAULT constraint, use the following SQL:
SQL Server / Oracle / MS Access:
ALTER TABLE Persons
ALTER COLUMN City DROP DEFAULT;
The DROP DATABASE command is used to delete an existing SQL database.
The following SQL drops a database named “testDB”:
DROP DATABASE testDB;
Note: Be careful before dropping a database. Deleting a database will result in loss of complete information stored in the database!
The DROP CONSTRAINT command is used to delete a UNIQUE, PRIMARY KEY, FOREIGN KEY, or CHECK constraint.
To drop a UNIQUE constraint, use the following SQL :
SQL Server / Oracle / MS Access:
ALTER TABLE Persons
DROP CONSTRAINT UC_Person;
MySQL:
ALTER TABLE Persons
DROP INDEX UC_Person;
The DROP COLUMN command is used to delete a column in an existing table.
The following SQL deletes the “ContactName” column from the “Customers” table:
ALTER TABLE Customers
DROP COLUMN ContactName;
The DROP COLUMN command is used to delete a column in an existing table.
The following SQL deletes the “ContactName” column from the “Customers” table:
ALTER TABLE Customers
DROP COLUMN ContactName;
The SELECT DISTINCT command returns only distinct (different) values in the result set.
The following SQL statement selects only the DISTINCT values from the “Country” column in the “Customers” table : Continue reading SQL SELECT DISTINCT Keyword
The DESC command is used to sort the data returned in descending order.
The following SQL statement selects all the columns from the “Customers” table, sorted descending by the “CustomerName” column : Continue reading SQL DESC Keyword
The DELETE command is used to delete existing records in a table.
The following SQL statement deletes the customer “Alfreds Futterkiste” from the “Customers” table:
DELETE FROM Customers WHERE CustomerName=‘Alfreds Futterkiste’;
Note: Be careful when deleting records in a table! Notice the WHERE clause in the DELETE statement. The WHERE clause specifies which record(s) should be deleted. If you omit the WHERE clause, all records in the table will be deleted!
It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:
The following SQL statement deletes all rows in the “Customers” table, without deleting the table. This means that the table structure, attributes, and indexes will be intact: Continue reading SQL DELETE Keyword