Database plays an important and crucial role. The most important 4GL capability of RDBMS is STRUCTURED QUERY LANGUAGE (SQL).
FEATURES OF STRUCTURED QUERY LANGUAGE (SQL)
- Recovery and Concurrency.
- Integrity Constraints.
CLASSIFICATION OF SQL STATEMENTS
SQL Database is differentiating into three sub-languages.
1. DATA DEFINITION LANGUAGE (DDL)
It is used to define the data structure in the database. It contains the necessary statements for creating, manipulating, altering and deleting the tables.
2. DATA MANIPULATION LANGUAGE (DML)
DML uses to manipulate the database. It contains statements and updates, deletes, insert, select data stored of data in the database.
3. DATA CONTROL LANGUAGE (DCL)
It is used for controlling data stored in the database. It contains statements to give permission, control transaction of data in the database.
RULES FOR SQL COMMANDS
- SQL statements are not case-sensitive.
- SQL statements can be in one or more files.
- Keywords cannot be abbreviated.
- Only one statement can be current at any time within the buffer and it can be run in the continuous line by placing a semicolon (;) at the end clause.
EXECUTING STRUCTURED QUERY LANGUAGE STATEMENTS
- 1Place a semicolon at the end of the last clause.
- 2Place a slash on the last line of the buffer.
- 3Place a slash at the SQL prompt.
- Issue a SQL * Plus RUN command at the SQL prompt.
PROPERTIES OF A TABLE
- The table creates at any time.
- There is no need to specify the size of the table.
- The table structure modifies any time.
- Tables may acquire more space automatically. If the initial size is fill up.
RULES TO NAME A TABLE
- The name must begin with a letter A-Z or a-z.
- You can use either upper case or lower case letters both are same.
- The length of table name is up to 30 characters.
- The name is not a SQL pre-reserve word.