Αποτελέσματα Αναζήτησης
•Overview of the SQL Query Language •SQL Data Definition •Basic Query Structure of SQL Queries •Additional Basic Operations •Set Operations •Null Values
1.1 Data Definition Language (DDL) The Data Definition Language (DDL) manages table and index structure. The most basic items of DDL are the CREATE, ALTER, RENAME and DROP statements: • CREATE creates an object (a table, for example) in the database. • DROP deletes an object in the database, usually irretrievably.
SQL allows users to access data in relational database management systems, such as Oracle, Sybase, Informix, Microsoft SQL Server, Access, and others, by allowing users to describe the data the user wishes to see. SQL also allows users to define the data in a database, and manipulate that data.
For example, to add one to the weight of an observation in the kids table where id is 101311 and age is between 9 and 10, we could use: UPDATE kids SET weight=weight + 1 WHERE id=’101311’ AND age BETWEEN 9 and 10; To change some of the values of columns of a table, you can use the UPDATE command.
access data from the database. The Structured Query Language (SQL) is the most popular query language used by major relational database management systems such as MySQL, ORACLE, SQL Server, etc. SQL is easy to learn as the statements comprise of . descriptive English words and are not case sensitive. We can create and interact with a database ...
Structured Query Language (SQL) is made up of two sub-languages: SQL Data Manipulation Language (DML) SELECT statements perform queries. INSERT, UPDATE, DELETE statements modify the instance of a table. SQL Data Definition Language (DDL) CREATE, DROP statements modify the database schema. GRANT, REVOKE statements enforce the security model.
SQL is commonly used to: (1) Create databases and the objects within them. (2) Store data in databases. (3) Change and analyze data. (4) Get data back in reports, web pages, etc.
