Overview of SQL

SQL is nonprocedural language for accessing a database. You run SQL statements commands to perform various tasks, such as retrieving data from tables in Oracle Database XE. The SQL language automatically handles how to navigate the database and perform the desired task. All database operations are performed using SQL statements. With SQL statements you can perform the following:

■ Query, insert, and update data in tables

■ Format, perform calculations on, store, and print from query results

■ Examine table and object definitions

Oracle SQL statements are divided into several categories:

 ■ Data Manipulation Language (DML) statements These statements query, insert, update, and delete data in tables.

■ Transaction Control statements These statements commit or roll back the processing of transactions. A group of changes that you make is referred to as a transaction.

■ Data Definition Language (DDL) statements These statements create, alter, and drop database objects.

A statement consists partially of SQL reserved words, which have special meaning in SQL and cannot be used for any other purpose. For example, SELECT and UPDATE are reserved words and cannot be used as table names.

List of the SQL reserved words

 ACCESS, ADD*, ALL*, ALTER*, AND*, ANY*, AS*, ASC*, AUDIT

 BETWEEN*, BY*, CHAR*, CHECK*, CLUSTER, COLUMN, COMMENT, COMPRESS, CONNECT*, CREATE*, CURRENT*

 DATE*, DECIMAL*, DEFAULT*, DELETE*, DESC*, DISTINCT*, DROP*

 ELSE*, EXCLUSIVE, EXISTS

 FILE, FLOAT*, FOR*, FROM*

 GRANT*, GROUP*

 HAVING*

 IDENTIFIED, IMMEDIATE*, IN*, INCREMENT, INDEX, INITIAL, INSERT*, INTERSECT*, INTO*, IS*

 LEVEL*, LIKE*, LOCK, LONG

 MAXEXTENTS, MINUS, MLSLABEL, MODE, MODIFY

 NOAUDIT, NOCOMPRESS, NOT*, NOWAIT, NULL*, NUMBER

 OF*, OFFLINE, ON*, ONLINE, OPTION*, OR*, ORDER*

 PCTREE, PRIOR*, PRIVLEGES*, PUBLIC*

 RAW, RENAME, RESOURCE, REVOKE*, ROW, ROWID, ROWNUM, ROWS*

SSELECT*, SESSION*, SET*, SHARE, SIZE*, SMALLINT*, START, SUCCESSFUL, SYNONYM, SYSDATE

TABLE*, THEN*, TO*, TRIGGER

UID, UNION*, UNIQUE*, UPDATE*, USER*

VALIDATE, VALUES*, VARCHAR*, VARCHAR2, VIEW*

WHENEVER*, WHERE, WITH*