Monday, November 3, 2014

Data Definition Language for Laptop Bekas

Laptop Bekas

The data definition language concept for laptop bekas in and name was first introduced in relation to the Codasyl database model, where the schema of the database was written in a language syntax describing the records, fields, and sets of the user data model.Later it was used to refer to a subset of Structured Query Language (SQL) for creating tables and constraints. SQL-92 introduced a schema manipulation language and schema information tables to query schemas. These information tables were specified as SQL/Schemata in SQL:2003. The term DDL is also used in a generic sense to refer to any formal language for describing data or information structures.

Many data description languages use a declarative syntax to define fields and data types. SQL, however, uses a collection of imperative verbs whose effect is to modify the schema of the database by adding, changing, or deleting definitions of tables or other objects. These statements can be freely mixed with other SQL statements, so the DDL is not truly a separate language.

To make a new database, table, index, or stored procedure.

A CREATE statement in SQL creates an object in a relational database management system (RDBMS). In the SQL 1992 specification, the types of objects that can be created are schemas, tables, views, domains, character sets, collations, translations, and assertions. Many implementations extend the syntax to allow creation of additional objects, such as indexes and user profiles. Some systems (such as PostgreSQL) allow CREATE, and other DDL commands, inside a transaction and thus they may be rolled back.
CREATE TABLE statement

A commonly used CREATE command is the CREATE TABLE command. The typical usage is:

CREATE TABLE [table name] ( [column definitions] ) [table parameters].

column definitions: A comma-separated list consisting of any of the following
    Column definition: [column name] [data type] {NULL | NOT NULL} {column options}
    Primary key definition: PRIMARY KEY ( [comma separated column list] )
    Constraints: {CONSTRAINT} [constraint definition]
    RDBMS specific functionality
For example, the command to create a table named employees with a few sample columns would be:
CREATE TABLE employees (
    id            INTEGER      PRIMARY KEY,
    first_name    VARCHAR(50) NOT NULL,
    last_name     VARCHAR(75) NOT NULL,
    fname         VARCHAR(50) NOT NULL,
    dateofbirth   DATE         NULL

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