mysql

Synopsis

To get introduced to SQL, we first need to know about Databases and Database Management Systems(DBMS). Data is basically a collection of facts related to some object. A Database is a collection of small units of data arranged in a systematic manner. A Relational Database Management System is a collection of tools that allows the users to manipulate, organize and visualize the contents of a database while following some standard rules that facilitate fast response between the database and the user side.

After getting introduced to the concept of data, databases and DBMS/RDBMS, we can finally learn about SQL. SQL or Structured Query Language is basically the language that we (the user) use to communicate with the Databases and get our required interpretation of data out of it. It is used for storing, manipulating and retrieving data out of a database.

SQL Features

The following functionalities can be performed on a database using SQL:

Create a Database or Delete a Database
Create a table or Alter a table or Delete a table from a Database
SELECT data from tables
INSERT data into tables
UPDATE data in tables
DELETE data from tables
Create Views in the database
Execute various aggregate functions

Basic SQL

Create Database and drop database

COMMAND	SYNTAX	DESCRIPTION
CREATE DATABASE	CREATE DATABASE database-name	Used to create new SQL database in the server
DROP DATABASE	CREATE DATABASE database-name	Used to drop the existing database

String Datatype

The table below lists all the String datatype available in SQL, along with their descriptions:

Datatype	Description
CHAR(size)	A fixed-length string containing numbers, letters or special characters. Length may vary from 0-255.
VARCHAR(size)	Variable-length string where the length may vary from 0-65535. Similar to CHAR.
TEXT(size)	Can contain a string of size up to 65536 bytes.
TINY TEXT	Can contain a string of up to 255 characters.
MEDIUM TEXT	Can contain a string of up to 16777215 characters.
LONG TEXT	Can contain a string of up to 4294967295 characters.
BINARY(size)	Similar to CHAR() but stores binary byte strings.
VARBINARY(size)	Similar to VARCHAR() but stores binary byte strings.
BLOB(size)	Holds blobs up to 65536 bytes.
TINYBLOB	It is used for Binary Large Objects and has a maximum size of 255bytes.
MEDIUMBLOB	Holds blobs up to 16777215 bytes.
LONGBLOB	Holds blobs upto 4294967295 bytes.
ENUM(val1,val2)	String object that can have only 1 possible value from a list of size at most 65536 values in an ENUM list. If no value is inserted, a blank value is inserted.
SET(val1,val2,…)	String object with 0 or more values, chosen from a list of possible values with a maximum limit of 64 values.

Numeric Datatype:

The table below lists all the Numeric Datatype in SQL along with their descriptions:

Datatype	Description
BIT(size)	Bit-value type, where size varies from 1 to 64. Default value: 1
INT(size)	Integer with values in the signed range of -2147483648 to 2147483647 and values in the unsigned range of 0 to 4294967295.
TINYINT(size)	Integer with values in the signed range of -128 to 127 and values in the unsigned range of 0 to 255.
SMALLINT(size)	Integer with values in the signed range of -32768 to 32767 and values in the unsigned range of 0 to 65535.
MEDIUMINT(size)	Integer with values in the signed range of -8388608 to 8388607 and values in the unsigned range of 0 to 16777215.
BIGINT(size)	Integer with values in the signed range of 9223372036854775808 to 9223372036854775807 and values in the unsigned range of 0 to 18446744073709551615.
BOOLEAN	Boolean values where 0 is considered as FALSE and non-zero values are considered TRUE.
FLOAT (p)	The floating-point number is stored. If the precision parameter is set between 0 to 24, the type is FLOAT() else if it lies between 25 to 53, the datatype is DOUBLE().
DECIMAL(size,d)	Decimal number with a number of digits before decimal place set by size parameter, and a number of digits after the decimal point set by d parameter. Default values: size = 10, d = 10. Maximum Values: size = 65, d = 30.

Date/Time Datatype:

The datatype available in SQL to handle Date/Time operations effectively are called the Date/Time datatype.
The table listed below all the Date/Time variables in SQL along with their description:

Datatype	Description
DATE	Stores date in YYYY-MM-DD format with dates in the range of ‘1000-01-01’ to ‘9999-12-31’.
TIME(fsp)	Stores time in hh:mm:ss format with times in the range of ‘-838:59:59’ to ‘838:59:59’.
DATETIME(fsp)	Stores a combination of date and time in YYYY-MM-DD and hh:mm:ss format, with values in the range of ‘1000-01-01 00:00:00’ to ‘9999-12-31 23:59:59’.
TIMESTAMP(fsp)	It stores values relative to the Unix Epoch, basically a Unix Timestamp. Values lie in the range of ‘1970-01-01 00:00:01’ UTC to ‘2038-01-09 03:14:07’ UTC.
YEAR	Stores values of years as a 4digit number format, with a range lying between -1901 to 2155.

Tables

COMMAND	SYNTAX	DESCRIPTION
CREATE TABLE	CREATE TABLE table_name (column1 datatype,column2 datatype,column3 datatype)	Used to create new table
DROP DATABASE	CREATE DATABASE database-name	Used to drop the existing database
TRUNCATE TABLE	TRUNCATE TABLE table_name	used to delete the data inside a table, but not the table itself.

Alter Table

COMMAND	SYNTAX	DESCRIPTION
ALTER TABLE ADD	ALTER TABLE table_name ADD column_name datatype	Used to add column in existing table
ALTER TABLE DROP	ALTER TABLE table_name DROP COLUMN column_name	Used to drop column in existing table
ALTER TABLE MODIFY	ALTER TABLE table_name MODIFY COLUMN column_name datatype	Used to modify column in existing table

Insert Table

COMMAND	SYNTAX	DESCRIPTION
INSERT INTO	INSERT INTO table_name (column1, column2, column3, …) VALUES (value1, value2, value3, …);	Used to insert data for particular columnn to add new records into existing table
INSERT INTO	INSERT INTO table_name VALUES (value1, value2, value3, …);	used to insert new record in existing table with all column

Update Table

COMMAND	SYNTAX	DESCRIPTION
UPDATE	UPDATE table_name SET column1 = value1, column2 = value2, … WHERE condition;	Used to update data for particular row for existing records in existing table
UPDATE	UPDATE table_name SET column1 = value1, column2 = value2, … ;	Used to update data for all row exist in existing table

Delete Table

COMMAND	SYNTAX	DESCRIPTION
DELETE	DELETE FROM table_name WHERE condition;	Used to delete data for particular row for existing records in existing table
DELETE	DELETE FROM table_name;	Used to delete data for all row exist in existing table

Important Sql Keywords

Keyword	Description	Example
ADD	Will add a new column to an existing table.	ALTER TABLE student ADD email_address VARCHAR(255)
ALTER TABLE	Adds edits or deletes columns in a table	ALTER TABLE student DROP COLUMN email_address
ALTER COLUMN	Can change the datatype of a table’s column	ALTER TABLE student ALTER COLUMN phone VARCHAR(15)
AS	Renames a table/column with an alias existing only for the query duration.	SELECT name AS student_name, phone FROM student
ASC	Used in conjunction with ORDER BY to sort data in ascending order.	SELECT column1, column2, … FROM table_name ORDER BY column1, column2, … ASC
DESC	Used in conjunction with ORDER BY to sort data in descending order.	SELECT column1, column2, … FROM table_name ORDER BY column1, column2, … DESC
CHECK	Constrains the value which can be added to a column.	CREATE TABLE student(fullName varchar(255), age INT, CHECK(age >= 18))
CREATE DATABASE	Creates a new database.	CREATE DATABASE student;
DEFAULT	Sets the default value for a given column.	CREATE TABLE products(ID int, name varchar(255) DEFAULT ‘Username’, from date DEFAULT GETDATE())
DELETE	Delete values from a table.	DELETE FROM users WHERE user_id= 674
DROP COLUMN	Deletes/Drops a column from a table.	ALTER TABLE student DROP COLUMN name
DROP DATABASE	Completely deletes a database with all its content within.	DROP DATABASE student
DROP DEFAULT	Removes a default value for a column.	ALTER TABLE student ALTER COLUMN age DROP DEFAULT
DROP TABLE	Deletes a table from a database.	DROP TABLE students
FROM	Determines which table to read or delete data from.	SELECT * FROM students
IN	Used with WHERE clause for multiple OR conditionals.	SELECT * FROM students WHERE name IN(‘Scaler’, ‘Interviewbit’,‘Academy’)
ORDER BY	Used to sort given data in Ascending or Descending order.	SELECT * FROM student ORDER BY age ASC
SELECT DISTINCT	Works in the same war as SELECT, except that only unique values are included in the results.	SELECT DISTINCT age from student
TOP	Used in conjunction with SELECT to select a fixed number of records from a table.	SELECT TOP 5 * FROM students
VALUES	Used along with the INSERT INTO keyword to add new values to a table.	INSERT INTO Customers (CustomerName, City, Country) VALUES (‘Cardinal’, ‘Stavanger’, ‘Norway’)
WHERE	Filters given data based on some given condition.	SELECT * FROM students WHERE age >= 18
UNIQUE	Ensures that all values in a column are different.	UNIQUE (ID)
UNION	Used to combine the result-set of two or more SELECT statements.	SELECT column_name(s) FROM Table1 UNION SELECT column_name(s) FROM Table2
UNION ALL	Combines the result set of two or more SELECT statements(it allows duplicate values)	SELECT City FROM table1 UNION ALL SELECT City FROM table2 ORDER BY City;
SELECT TOP	Used to specify the number of records to return.	SELECT TOP 3 * FROM Students
LIMIT	Puts a restriction on how many rows are returned from a query.	SELECT * FROM table1 LIMIT 3
UPDATE	Modifies the existing records in a table.	UPDATE Customers SET ContactName = ‘Scaler’, City = ‘India’ WHERE CustomerID = 1;
SET	Used with UPDATE to specify which columns and values should be updated in a table.	UPDATE Customers SET ContactName = ‘Scaler’, City= ‘India’ WHERE
IS NULL	Column values are tested for NULL values using this operator.	SELECT CustomerName, ContactName, Address FROM Customers WHERE Address IS NULL
LIKE	Used to search for a specified pattern in a column.	SELECT * FROM Students WHERE Name LIKE ‘a%’
ROWNUM	Returns a number indicating the order in which Oracle selects the row from a table or set of joined rows.	SELECT * FROM Employees WHERE ROWNUM < 10;
GROUP BY	Groups rows that have the same values into summary rows.	SELECT COUNT(StudentID), State FROM Students GROUP BY State
HAVING	Enables the user to specify conditions that filter which group results appear in the results.	HAVING COUNT(CustomerID) > 5

Clauses in SQL

Name	Description	Example
WHERE	Used to select data from the database based on some conditions.	SELECT * from Employee WHERE age >= 18;
AND	Used to combine 2 or more conditions and returns true if all the conditions are True.	SELECT * from Employee WHERE age >= 18 AND salary >= 45000 ;
OR	Similar to AND but returns true if any of the conditions are True.	Select * from Employee where salary >= 45000 OR age >= 18
LIKE	Used to search for a specified pattern in a column.	SELECT * FROM Students WHERE Name LIKE ‘a%’;
LIMIT	Puts a restriction on how many rows are returned from a query.	SELECT * FROM table1 LIMIT 3;
ORDER BY	Used to sort given data in Ascending or Descending order.	SELECT * FROM student ORDER BY age ASC
GROUP BY	Groups rows that have the same values into summary rows.	SELECT COUNT(StudentID), State FROM Students GROUP BY State;
HAVING	It performs the same as the WHERE clause but can also be used with aggregate functions.	SELECT COUNT(ID), AGE FROM Students GROUP BY AGE HAVING COUNT(ID) > 5;

SQL Operators

There are 3 main types of operators: Arithmetic, Comparision and Logical operators, each of which will be described below.

Arithmetic Operators

Arithmetic Operators allows the user to perform arithmetic operations in SQL. The table below shows the list of arithmetic operators available in SQL:

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulo

Bitwise Operators

Bitwise operators are used to performing Bit manipulation operations in SQL. The table below shows the list of bitwise operators available in SQL:

Operator	Description
&	Bitwise AND
!\|	Bitwise OR
^	Bitwise XOR

Relational Operators

Relational operators are used to performing relational expressions in SQL, i.e those expressions whose value either result in true or false. The table below shows the list of relational operators available in SQL:

Operator	Description
=	Equal to
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to
<>	Not equal to

Compound Operators

Compound operators are basically a combination of 2 or more arithmetic or relational operator, which can be used as a shorthand while writing code. The table below shows the list of compound operators available in SQL:

Operator	Description
+=	Add equals
-=	Subtract equals
*=	Multiply equals
/=	Divide equals
%=	Modulo equals
&=	AND equals
!\|=	OR equals
^=	XOR equals

Logical Operators

Logical operators are used to combining 2 or more relational statements into 1 compound statement whose truth value is evaluated as a whole. The table below shows the SQL logical operators with their description:

Operator	Description
ALL	Returns True if all subqueries meet the given condition.
AND	Returns True if all the conditions turn out to be true
ANY	True if any of the subqueries meet the given condition
BETWEEN	True if the operand lies within the range of the conditions
EXISTS	True if the subquery returns one or more records
IN	Returns True if the operands to at least one of the operands in a given list of expressions
LIKE	Return True if the operand and some given pattern match.
NOT	Displays some record if the set of given conditions is False
OR	Returns True if any of the conditions turn out to be True
SOME	Returns True if any of the Subqueries meet the given condition.

Function in sql

SQL Server Numeric Functions

The table below lists some of the Numeric functions in SQL with their description:

Name	Description
ABS	Returns the absolute value of a number.
ASIN	Returns arc sine value of a number.
AVG	Returns average value of an expression.
COUNT	Counts the number of records returned by a SELECT query.
EXP	Returns e raised to the power of a number.
FLOOR	Returns the greatest integer <= the number.
RAND	Returns a random number.
SIGN	Returns the sign of a number.
SQRT	Returns the square root of a number.
SUM	Returns the sum of a set of values.

SQL Server Date Functions

The table below lists some of the Date functions in SQL with their description:

Name	Description
CURRENT_TIMESTAMP	Returns current date and time.
DATEADD	Adds a date/time interval to date and returns the new date.
DATENAME	Returns a specified part of a date(as a string).
DATEPART	Returns a specified part of a date(as an integer).
DAY	Returns the day of the month for a specified date.
GETDATE	Returns the current date and time from the database.

SQL Server Advanced Functions

The table below lists some of the Advanced functions in SQL with their description:

Name	Description
CAST	Typecasts a value into specified datatype.
CONVERT	Converts a value into a specified datatype.
IIF	Return a value if a condition evaluates to True, else some other value.
ISNULL	Return a specified value if the expression is NULL, else returns the expression.
ISNUMERIC	Checks if an expression is numeric or not.
SYSTEM_USER	Returns the login name for the current user
USER_NAME	Returns the database user name based on the specified id.

Joins in SQL

COMMAND	SYNTAX	DESCRIPTION
INNER JOIN	SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name;	selects records that have matching values in both tables.
LEFT JOIN	SELECT column_name(s) FROM table1 LEFT JOIN table2 ON table1.column_name = table2.column_name;	returns all records from the left table (table1), and the matching records from the right table (table2). The result is 0 records from the right side, if there is no match.
RIGHT JOIN	SELECT column_name(s) FROM table1 RIGHT JOIN table2 ON table1.column_name = table2.column_name;	returns all records from the right table (table2), and the matching records from the left table (table1). The result is 0 records from the left side, if there is no match.
FULL JOIN	SELECT column_name(s) FROM table1 FULL OUTER JOIN table2 ON table1.column_name = table2.column_name WHERE condition;	returns all records when there is a match in left (table1) or right (table2) table records.
SELF JOIN	SELECT column_name(s) FROM table1 T1, table1 T2 WHERE condition;	A self join is a regular join, but the table is joined with itself.