SQL Basics: Overview and Introduction

Rumman Ansari   Software Engineer   2024-07-05 05:39:32   8231  Share
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What is SQL

SQL stands for Structured Query Language and can be pronounced as SQL or sequel – (Structured Query Language) . Defined, SQL is a query language used for accessing and modifying information in one or more data tables and rows of a database.

SQL DataBase

In a simple manner, SQL is a non-procedural, English-like language that processes data in groups of records rather than one record at a time. Few SQL functions of are:

  • Store data
  • Modify data
  • Retrieve data
  • Delete data
  • Create tables and other database objects

A Brief History of SQL

  • 1970 − Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases.

  • 1974 − Structured Query Language appeared.

  • 1978 − IBM worked to develop Codd's ideas and released a product named System/R.

  • 1986 − IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software which later came to be known as Oracle.

SQL Database Design

IBM first developed SQL in 1970s. Also it is an ANSI/ISO standard. It has become a Standard Universal Language used by most of the relational database management systems (RDBMS). Some of the RDBMS systems are: Oracle, Microsoft SQL server, Sybase etc.

Most of these have provided their own implementation extensions, thus enhancing their RDBMS system features and making it a powerful tool. These RDBMS systems, all use the popular SQL commands SELECT, UPDATE, DELETE, INSERT, WHERE in similar format.

SQL Database Table

SQL database is constructed of a number of tables. In a business, SQL tables would be used to divide and simplify the different areas of the operation: Table for Customers, one for Vendors, Employees and so on.

SQL Database Table Columns

Each SQL table is made up of a number of columns, referred to as fields and run along the top of the table. Sql columns or fields have their content (object/data/info) defined into character types; such as text, date, numeric, integer, length to name a few.

SQL Database Table Rows

Each SQL table row, referred to a record, is located in the left column of the table. Sql record row will contain a string of data containing data matching up to each column field across the top. So, in a Customer table each customer record would consist of one row with data for the customer ID number, customer name, address, phone ... email and so on.

Simple Overview of various SQL query

SQL Query Types

SELECT Statement Retrieve records from a table
SELECT LIMIT Statement Retrieve records from a table and limit results
SELECT TOP Statement Retrieve records from a table and limit results
INSERT Statement Insert records into a table
UPDATE Statement Update records in a table
DELETE Statement Delete records from a table
TRUNCATE TABLE Statement Delete all records from a table (no rollback)
UNION Operator Combine 2 result sets (removes duplicates)
UNION ALL Operator Combine 2 result sets (includes duplicates)
INTERSECT Operator Intersection of 2 result sets
MINUS Operator Result set of one minus the result set of another
EXCEPT Operator Result set of one minus the result set of another

SQL Comparison Operators

Comparison Operators Operators such as =, <>, !=, >, <, and so on

SQL Joins

JOIN Tables Inner and Outer joins

SQL Aliases

ALIASES Create a temporary name for a column or table

SQL Clauses

DISTINCT Clause Retrieve unique records
FROM Clause List tables and join information
WHERE Clause Filter results
ORDER BY Clause Sort query results
GROUP BY Clause Group by one or more columns
HAVING Clause Restrict the groups of returned rows

SQL Functions

COUNT Function Return the count of an expression
SUM Function Return the sum of an expression
MIN Function Return the min of an expression
MAX Function Return the max of an expression
AVG Function Return the average of an expression

SQL Conditions

AND Condition 2 or more conditions to be met
OR Condition Any one of the conditions are met
AND & OR Combining AND and OR conditions
LIKE Condition Use wildcards in a WHERE clause
IN Condition Alternative to multiple OR conditions
NOT Condition Negate a condition
IS NULL Condition Test for NULL value
IS NOT NULL Condition Test for NOT NULL value
BETWEEN Condition Retrieve within a range (inclusive)
EXISTS Condition Condition is met if subquery returns at least one row

SQL Tables and Views

CREATE TABLE Create a table
CREATE TABLE AS Create a table from another table's definition and data
ALTER TABLE Add, modify or delete columns in a table; rename a table
DROP TABLE Delete a table
GLOBAL TEMP Tables Tables that are distinct within SQL session
LOCAL TEMP Tables Tables that are distinct within modules and embedded SQL program
SQL VIEW Virtual tables (views of other tables)

No Program Data.

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