A structured query is a query based on a text column and a
structured data column. The structured data column is usually in the same table
as the text column. For example, you might use a structured query to retrieve
documents on a certain subject that were written after a certain date, where
the document content is in a text column and date information is in a
structured data column.
Structured Query Language(SQL) as we all
know is the database language by the use of which we can perform certain
operations on the existing database and also we can use this language to create
a database. SQL uses certain commands like Create, Drop, Insert etc. to carry
out the required tasks.
These SQL commands are mainly categorized
into four categories as discussed below:
1.DDL(Data Definition Language) : DDL or
Data Definition Language actually consists of the SQL commands that can be used
to define the database schema. It simply deals with descriptions of the
database schema and is used to create and modify the structure of database
objects in database.
of DDL commands:
·CREATE – is used to
create the database or its objects (like table, index, function, views, store
procedure and triggers).
·DROP – is used to
delete objects from the database.
·ALTER-is used to alter
the structure of the database.
·TRUNCATE–is used to remove
all records from a table, including all spaces allocated for the records are
·COMMENT –is used to
add comments to the data dictionary.
used to rename an object existing in the database.
2.DML(Data Manipulation Language)
SQL commands that deals with the manipulation of data present in database
belong to DML or Data Manipulation Language and this includes most of the SQL
·SELECT – is used to
retrieve data from the a database.
·INSERT – is used to
insert data into a table.
·UPDATE – is used to
update existing data within a table.
·DELETE – is used to
delete records from a database table.
3.DCL(Data Control Language) : DCL
includes commands such as GRANT and REVOKE which mainly deals with the rights,
permissions and other controls of the database system.
of DCL commands:
access privileges to database.
access privileges given by using the GRANT command.
4.TCL(transaction Control Language)
commands deals with the transaction within the database.
of TCL commands:
·COMMIT– commits a
·ROLLBACK– rollbacks a
transaction in case of any error occurs.
·SAVEPOINT–sets a savepoint
within a transaction.
characteristics for the transaction.
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