Data Definition Language (DDL)
Definition – What will knowledge Definition Language (DDL)mean?– An information theme is such as by a group of definitions that are expressed by a special language referred to as a knowledge definition language (DDL). The result of compilation Of DDL statements is a set of tables which are stored in a special file called data dictionary (directory).
whenever data is read or modified in the database system, the data directory is consulted. The DDL provides a group of definitions to specify the storage structure and access strategies utilized by the information system.
Data Definition Language (DDL) Function
an ideal DDL should perform the following function-
1.it should identify the types of data division such as data item, segment, record, and database-file.
2.it should give a unique name to each data -item,record-type,file-type, database, and other data subdivision.
3.it should specify the proper data types.
4.it should specify how the record types are related to making structures.
5.it may define the type of encoding the program uses in the data items(binary, character, bit, string.etc.) This should not be confused with the encoding employed in physical representation.
6.it may define the length of the data items.
7.it may define the range of values that a data-item can assume.
8.it may specify means of checking for errors in the data.
9.it may specify privacy locks for preventing unauthorized reading or modification of the data.
10. A logical data definition should not specify addressing, indexing, or searching techniques or specify the placement of data on the storage units, because these topics are in the domain of physical, not logical, organization.
Commonly used DDL in SQL query (Data Definition Language (DDL)
CREATE: This command builds a replacement table and encompasses a predefined syntax. The produce statement syntax is produce TABLE [table name] ([column definitions]) [table parameters]. produce TABLE worker (Employee Id whole number PRIMARY KEY, given name CHAR (50) NULL, family name CHAR (75) NOT NULL).
ALTER: associate degree alter command modifies associate degree existing info table. This command will add up the further column, drop existing columns and even modification the information kind of columns concerned during an info table. associate degree alters command syntax is ALTER object sort object name parameters. ALTER TABLE worker ADD DOB Date.
Read also computer science & technology related article –