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Posts Tagged ‘SQL’

What is SQL, PL/SQL, T-SQL and difference between them

May 3, 2015 14 comments

Today I got an email from a student who is pursuing his Bachelors degree in Computer Application (BCA). He visited my blog and sent me an email regarding his confusion with terms like SQL, T-SQL, PL/SQL, and asked me what is differences between them and how are they related? I had a chat with him and told the basic differences, but he further asked me how they are related to Microsoft SQL Server, Oracle, MySQL, etc? As he is studying SQL only based upon Oracle in his course curriculum, these all terms were not clear to him, so I cleared all his doubts while chatting with him.

After a while I had a same reminiscence that when I was a student I also had these doubts and confusions, and there was nobody to guide me, but I gradually came to know about this and it took some time. Thus, I’am taking this opportunity to put all these things together here in a single blog post for my readers (specially students) and for my reference as well.
 

–> SQL: stands for Structured Query Language and is pronounced as Sequel, and in early days it was also known as SEQUEL only.

– IBM in early 1970s developed SEQUEL which stands for Structured English QUEry Langauge for their RDBMS. The acronym was later changed to SQL, as SEQUEL was already trademarked by some UK based aircraft company.
 

–> PL/SQL: stands for Procedural Language/Structured Query Language and is used with Oracle database to create PL/SQL units such as Procedures, Functions, Packages, Types, Triggers, etc. which are stored in the database for reuse by applications that use any of the Oracle Database programmatic interfaces.

– Oracle in 1970s known as “Relational Software” saw SQL potential and influenced by Boyce, Codd and Chamberlin developed their own RDBMS product which was commercially available as Oracle Database. Oracle is supported on many Operating Systems like Windows, Linux, Solaris, AIX, OpenVMS, etc. [Oracle Database]
 

–> DB2: IBM during early 1980s made SQL commercially available with its product known as IBM DB2 from its prototype “System R”. [IBM DB2]
 

–> SQL Standardization: Later in 1986 SQL was adopted as a Standard by ANSI (American National Standards Institute) as SQL-86, and today the latest Standard is known as SQL:2011

✔ As a standarg SQL should support following:

– Language elements: Clauses, Expressions, Predicates, Queries, Statements.
– Operators: =, , >, =, <=, BETWEEN, LIKE, IN, NOT IN, IS, IS NOT, AS, etc.
– Conditional expressions: CASE, IF ELSE
– Queries: which include SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, etc.
– Data Types: Numeric, Char, Bit, Date and Time
– NULL or 3VL (Three value Logic)
– DDL, DML, TCL
 

–> T-SQL: stands for Transact-SQL, and is Sybase & Microsoft’s proprietary extension. T-SQL is very similar to PL/SQL, one can create T-SQL units such as Procedures, Functions, Types, Triggers, etc. as mentioned above.

– In 1987 Sybase shipped their first RDBMS product known as Sybase SQL Server. [Sybase]

– In 1988-89 Microsoft had an agreement with Sybase and ported the Sybase RDBMS to OS/2 platform and marketed it as Microsoft SQL Server 1.0, which was equivalent to Sybase SQL Server 3.0. [Microsoft SQL Server]

– In 1993 Sybase and Microsoft dissolved their partnership, and Microsoft bought the SQL Server code base from Sybase and both went different streams to develop their own product.

– Till SQL Server 2000 Microsoft has Sybase code base, and this was completely written in SQL Server 2005.

– Microsoft SQL Server is only supported on Windows Operating Systems.
 

–> MySQL: was founded by a Swedish Company MySQL AB in 1995 and is the most widely used open-source RDBMS. The MySQL development project has made its source code available under the terms of the GNU General Public License. MySQL does not currently comply with the full SQL standard. In 2008 Oracle corporation completely acquired MySQL. MySQL is supported on many Operating Systems like Windows, Linux, Solaris, OS X and FreeBSD. [MySQL.com]
 

–> FoxPRO and dBase: were very popular DataBase Management System (DBMS) products in mid 1980s and 1990s. They lack some RDBMS features and are out of support now, but are still being used in various legacy systems.

– FoxPRO is supported by Microsoft and was a text-based Procedural programming language and DBMS, for MD DOS, Windows, and UNIX. Microsoft Visual FoxPRO 9.0 being the latest and probably the last version published in 2007. [FoxPRO msdn]

– dBase was a very popular DBMS package including core Database engine, a Query system, a Forms engine and a xBase programming language with *.dbf file format. [dBase.com]
 

–> Here is a complete timeline that shows SQL and how it got evolved as different Products by different Vendors/Companies (click on the image to expand):
 

RDBMS_timeline.svg
 

–> There are many other popular SQL Products/System softwares available in market, and major of them are:
1. Oracle database
2. Microsoft SQL Server
3. IBM DB2
4. MySQL
5. PostgreSQL
6. Teradata
 


 

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An introduction to SQL and its Components

February 3, 2009 Leave a comment

–>Introduction:

SQL or Structured Query Language is a language that provides an interface to relational database systems. The proper pronunciation of SQL is “ess cue ell,” and not “sequel” as is commonly heard. SQL was developed by IBM in the 1970s for use in System R, and is a de facto standard, as well as an ISO and ANSI standard. In common usage SQL also encompasses DML (Data Manipulation Language), for INSERTs, UPDATEs, DELETEs and DDL (Data Definition Language), used for creating and modifying tables and other database structures. The development of SQL is governed by standards. A major revision to the SQL standard was completed in 1992, called SQL2. SQL3 support object extensions and are (partially?) implemented in Oracle8 and 9i.

SQL (Structured Query Language) is a database computer language designed for managing data in relational database management systems (RDBMS). Its scope includes data query and update, schema creation and modification, and data access control. SQL was one of the first languages for Edgar F. Codd’s relational model in his influential 1970 paper, “A Relational Model of Data for Large Shared Data Banks” and became the most widely used language for relational databases.
 

–>Language elements:

The SQL language is sub-divided into several language elements, including:

1. Clauses which are in some cases optional, constituent components of statements and queries.

2. Expressions which can produce either scalar values or tables consisting of columns and rows of data.

3. Predicates which specify conditions that can be evaluated to SQL three-valued logic (3VL) Boolean truth values and which are used to limit the effects of statements and queries, or to change program flow.

4. Queries which retrieve data based on specific criteria.

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

6. SQL statements also include the semicolon (“;”) statement terminator. Though not required on every platform, it is defined as a standard part of the SQL grammar.

7. Insignificant whitespace is generally ignored in SQL statements and queries, making it easier to format SQL code for readability.
 

–> Queries:

The most common operation in SQL is the query, which is performed with the declarative SELECT statement. SELECT retrieves data from one or more tables, or expressions. Standard SQL statements have no persistent effects on the database. Some non-standard implementations of SELECT can have persistent effects, such as the SELECT INTO syntax that exists in some databases.

Queries allow the user to describe desired data, leaving the database management system (DBMS) responsible for planning, optimizing, and performing the physical operations necessary to produce that result as it chooses.

A Query includes a list of columns to be included in the final result immediately following the SELECT keyword. An asterisk (“*”) can also be used to specify that the query should return all columns of the queried tables. SELECT is the most complex statement in SQL, with optional keywords and clauses that includes:

1. The FROM clause which indicates the table(s) from which data is to be retrieved. The FROM clause can include optional JOIN subclauses to specify the rules for joining tables.

2. The WHERE clause includes a comparison predicate, which restricts the rows returned by the query. The WHERE clause eliminates all rows from the result set for which the comparison predicate does not evaluate to True.

3. The GROUP BY clause is used to project rows having common values into a smaller set of rows. GROUP BY is often used in conjunction with SQL aggregation functions or to eliminate duplicate rows from a result set. The WHERE clause is applied before the GROUP BY clause.

4. The HAVING clause includes a predicate used to filter rows resulting from the GROUP BY clause. Because it acts on the results of the GROUP BY clause, aggregation functions can be used in the HAVING clause predicate.

5. The ORDER BY clause identifies which columns are used to sort the resulting data, and in which direction they should be sorted (options are ascending or descending). Without an ORDER BY clause, the order of rows returned by an SQL query is undefined.
 

–> A simple SELECT example:

SELECT *
FROM dbo.Book
WHERE price > 100.00
ORDER BY title;

 

–> With SQL you can:

– Create new Databases.
– Create new Tables in a database.
– Execute Queries against a database.
– Insert records in a database.
– Update records in a database.
– Delete records from a database.
– Retrieve data from a database.
– Create stored procedures in a database.
– Create views in a database.
– Set permissions on tables, procedures, and views.
 

For the complete history check my following [blog post].