added readme and ddl commands

Author: AnuragAnalog

README.md

@@ -0,0 +1,106 @@
+# MySQL cheatsheet
+
+I have even uploaded the .sql file which you can run and directly run them in the sql prompt.
+
+### General Commands
+To run sql files
+```sql
+source <filename>.sql;
+```
+
+## Data Definition Language (DDl)
+
+#### Create Database
+```sql
+create database cheatsheet;
+```
+
+#### Use Database
+```sql
+use cheatsheet;
+```
+
+#### Show Databases
+```sql
+show databases;
+```
+
+#### Create Table
+```sql
+create table employee
+(
+    employee_id int primary key,              -- Setting primary key(1st method)
+    first_name varchar(50),
+    last_name varchar(50),
+    dept_number int,
+    age int,
+    salary real
+);
+
+create table department
+(
+    dept_number int,
+    dept_name varchar(50),
+    dept_location varchar(50),
+    emp_id int,
+    primary key(dept_number)                -- Setting primary key(2nd method)
+);
+```
+
+#### Show Tables
+```sql
+show tables;
+```
+
+#### Describe Table
+```sql
+describe employee;
+desc employee;
+show columns in employee;
+```
+
+#### Rename Table
+```sql
+rename table employee to employee_table;
+alter table employee_table rename to employee;
+```
+
+#### Renaming Column
+```sql
+alter table employee change column employee_id emp_id int;
+```
+
+#### Add Constraint to Column
+```sql
+alter table employee change column first_name first_name varchar(50) not null;
+```
+
+#### Add Column
+```sql
+alter table employee add column salary real;
+```
+
+#### Drop Column
+```sql
+alter table employee drop column salary;
+```
+
+#### Modify the Datatype of column
+```sql
+alter table employee modify column salary int;
+```
+
+#### Truncate Table
+```sql
+truncate employee;
+```
+
+#### Drop Table
+```sql
+drop table department;
+```
+
+#### Drop Database
+```sql
+drop database cheatsheet;
+```

ddl-commands.sql

@@ -0,0 +1,64 @@
+
+-- Creating database
+create database cheatsheet;
+
+-- Viewing the databases
+show databases;
+
+-- using the database
+use cheatsheet;
+
+create table employee
+(
+    employee_id int primary key,              -- Setting primary key(1st method)
+    first_name varchar(50),
+    last_name varchar(50),
+    dept_number int,
+    age int,
+    salary real
+);
+
+create table department
+(
+    dept_number int,
+    dept_name varchar(50),
+    dept_location varchar(50),
+    emp_id int,
+    primary key(dept_number)                -- Setting primary key(2nd method)
+);
+
+-- veiwing tables in the selected database
+show tables;
+
+-- print the structure of the table
+describe employee;
+desc employee;
+show columns in employee;
+
+-- renaming of table
+rename table employee to employee_table;
+alter table employee_table rename to employee;
+
+-- reanaming a column
+alter table employee change column employee_id emp_id int;
+
+-- add a constraint to column
+alter table employee change column first_name first_name varchar(50) not null;
+
+-- add column
+alter table employee add column salary real;
+
+-- drop a column
+alter table employee drop column salary;
+
+-- modify the datatype
+alter table employee modify column salary int;
+
+-- truncate a table
+truncate employee;
+
+-- drop table
+drop table department;
+
+-- drop database
+drop database cheatsheet;