SQL 5 Minutes Read

SQL CHEAT SHEET (5 Minutes Read of Structured Query Language (SQL))

SQL (Structured Query Language) is a standardised programming language used to manage relational databases and execute various operations on related data. SQL, which was developed in the 1970s, is now widely used not only by database administrators but also by developers building data integration scripts and data analysts wanting to set up and perform analytical queries. 

SQL is used to modify database table and index structures, add, update, and delete rows of data, and retrieve subsets of information from inside a database for transaction processing and analytics applications. Queries and other SQL operations take the form of statements, which are regularly used instructions. Select, add, insert, update, delete, create, change, and truncate are all SQL statements.

In this blog, we will learn how to perform basic operations in SQL. Get function for inserting data, update data, deleting data, grouping data, order data, etc. If you have started using SQL this is the best reference guide.

SQL Facts 

SQL stands for Structured Query Language. 

SQL is pronounced "sequel". 

SQL is a declarative language. 

SQL is used to access & manipulate data in databases. 

Top SQL DBs are MS SQL Server, Oracle, DB2, and MYSQL. 

Database Definitions 

RDBMS (Relational Database Management System) - Software that stores and manipulates data arranged in relational database tables. 

Table - A set of data arranged in columns and rows. The columns represent characteristics of stored data and the rows represent actual data entries. 

How to select data from a table 

SELECT <Column List> 

FROM <Table Name> 

WHERE <Search Condition> 

Example: SELECT FirstName, LastName, OrderDate 

FROM Orders WHERE OrderDate > '15/12/2020

SQL Commands Categories 

Data Query Language (DQL) 

• SELECT - Retrieve data from table(s) 

Data Manipulation Language (DML) 

• INSERT - Insert data into db table 
• UPDATE - Update data in db table 
• DELETE - Delete data from table 

Data Definition Language (DDL) 

• CREATE - Create db object (table, view, etc.) 
• ALTER - Modify db object (table, view, etc.) 
• DROP - Delete db object (table, view, etc.) 

Data Control Language (DCL) 

• GRANT - Assign privilege 
• REVOKE - remove privilege 

How to insert data in a table 

INSERT INTO <Table Name> 

(<Column List>) VALUES (<Values>)

 

Example: 

INSERT INTO Orders (FirstName, LastName, OrderDate) VALUES ('VXYZ', 'ABCDE', '15/12/2020'

How to update data in a table 

UPDATE <Table Name> 

SET <Column1>= <Value1>, <Column2> = <Value2>, 

WHERE <Search Condition> 

Example: 

UPDATE Orders 

SET FirstName = 'VXYZ', LastName 'Who' WHERE LastName='Wo' 

How to group data and use aggregates 

SELECT <Column List>, <Aggregate Function>(<Column Name>) 

FROM <Table Name> 

WHERE <Search Condition> 

GROUP BY <Column List> 

Example: 

SELECT LastName, SUM(OrderValue) 

FROM Orders 

WHERE OrderDate > '15/12/2020' 

GROUP BY LastName 

How to select data from more than one table 

SELECT <Column List> 

FROM <Table1> XYZ <Table2> 

ON <Table1>.<Column1>=<Table2>.<Column1> 

Example: 

SELECT Orders.LastName, Countries.CountryName 

FROM Orders JOIN Countries ON 

Orders.CountrylID = Countries.lID

How to delete data from a table 

DELETE FROM <Table Name> 

WHERE <Search Condition> 

Example: 

DELETE FROM Orders 

WHERE OrderDate < '15/12/2020' 

How to order data 

SELECT <Column List> 

FROM <Table Name>

WHERE <Search Condition>

ORDER BY <Column List>

Example: 

SELECT FirstName, 

LastName, OrderDate 

FROM Orders  

WHERE OrderDate > '15/12/2020'  

ORDER BY OrderDate 

Using UNION 

SELECT <Column List> FROM <Table1> 

UNION 

SELECT <Column List> FROM <Table2> 

Example: 

SELECT FirstName, LastName FROM Orders2020 

UNION 

SELECT FirstName, LastName FROM Orders2021 

CREATE TABLE 

CREATE TABLE <Table Name> 

( Column1 DataType,

Column2 DataType,

Column3 DataType,

...   )

CREATE TABLE Orders    

( FirstName CHAR(100), 

LastName CHAR(100), 

OrderDate DATE, 

OrderValue Currency ) 

Any comments or suggestions are welcome.

Thanks for reading this blog.