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DBMS Training & SQL Tutorial :
SQL Basics and SQL Data Types

apid   Theory you need to know! 

SQL Concepts :

  • SQL stands for Structured Query Language.

  • SQL statements cannot be executed without a DBMS.

  • SQL is used to perform various operations on the data in the database like creating, modifying & deleting tables, maintaining data integrity and retrieving the data.

  • For the RDBMS, an SQL program is just a single statement and is executed as a whole.

  • An SQL statement written on a Windows platform gives the same output on a Linux platform. Thus, SQL statements are platform independent however not necessarily database vendor independent.

  • SQL is a set level language as it operates upon a set of records. Languages that operate on one record at a time are known as record level languages.

SQL Environments :
  • Embedded and Dynamic SQL are the two types of SQL environments.

  • Through Embedded SQL, we can create programs that access the database through SQL statements embedded in it.

  • In Dynamic SQL, the SQL statements are not embedded in the program but are created dynamically.

  • If the names of the database objects change, it is easier to change the dynamic SQL statements as compared to the embedded SQL statements.

SQL Data Types :
  • SQL data types are the same across platforms. For example a INTEGER will occupy 4 bytes on both a Windows and a Linux platform.

  • The CLOB data type is used to store large amounts of formatted text like catalogs, brochures, books, etc.

  • The BINARY STRING data type can be used to store audio, video and image files. The data is stored in form of a sequence of bytes.

  • CHAR(length) is a fixed length character string data type.

  • BIT(length) data type can be used to store fixed length bit strings. However, BIT VARYING(length) can be used to store variable length bit strings.

  • A NULL value is used to represent unknown data.

  • A national character set literal is represented by preceding it by N (example N'Jack').

  • If we want to include single quotes in a string constant, it is written as two consecutive single quotes.

  • Two strings can be concatenated using two consecutive bar characters ( || ). For example, ('Mr. ' || 'Roger ' || 'Abraham') returns the string Mr. Roger Abraham.

  • Symbolic constants allow us to easily access frequently required information. For example, CURRENT_DATE gives us the date and CURRENT_TIME gives us the current time.

  • The POSITION(string1 IN string2) function returns the starting position of string1 in string2.


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