Structured Query Language

Stuctured query language (SQL) is

• The American National Standard Institute (ANSI) standard language for operating relational database
• Efficient, easy to learn and use
• Functionality complete (With SQL, you can define, retrieve, and manipulate data in tables

Sample of SQL syntax :

     select  employee_name, employee_number, salary

    from  employee_table

   where  salary > 1000000;

The SQL language is subdivided into several language elements, including:

• Clauses, which are constituent components of statements and queries. (In some cases, these are optional.)
• Expressions, which can produce either scalar values, or tables consisting of columns and rows of data.
• Predicates, which specify conditions that can be evaluated to SQL three-valued logic (3VL)(true/false/unknown) or Boolean truth values and which are used to limit the effects of statements and queries, or to change program flow. 

          Image below show you about 3VL :

          

• Statements, which may have a persistent effect on schemata and data, or which may control transactions, program flow, connections, sessions, or diagnostics.

SQL Statement consist of :

1. Data Manipulation Language, consist of several comment are :

• Select 
• Insert
• Update
• Delete
• Merge 

2. Data Definition Language, consist of several comment are :

• Create
• Alter
• Drop
• Rename
• Truncate
• Comment

3. Data Control Language, consist of several comment are :

• Grant
• Revoke

4. Transaction Control, consist of several comment are :

• Commit
• Rollback
• Savepoint