Merge pull request #10 from sanket95droid/constraints

#5 Added Constraints

Author: AnuragAnalog

README.md

@@ -462,6 +462,56 @@ release savepoint sv_pt;
 commit;
 ```
 
+## Constraints
+
+#### Not Null
+```sql
+alter table Employee
+change
+    Age
+    Age int NOT NULL;
+```
+
+#### Unique
+```sql
+alter table Employee
+add constraint u_q unique(ID);
+```
+```sql
+alter table Employee -- drop the constraint
+drop constraint u_q;
+```
+
+#### Primary Key
+```sql
+alter table Employee
+add constraint p_k primary key(ID);
+```
+```sql
+alter table Employee -- drop the constraint
+drop constraint p_k;
+```
+
+#### Check
+```sql
+alter table Employee
+add constraint Age check (age>=30);
+```
+```sql
+alter table Employee -- drop the constraint
+drop check Age;
+```
+
+#### Default
+```sql
+alter table Employee
+alter Age set default 10;
+```
+```sql
+alter table Employee -- drop the constraint
+alter Age drop default;
+```
+
 ## Cloning
 
 #### Duplicate a Table Schema

constraints.sql

@@ -0,0 +1,52 @@
+-- creating basic database layout for using constraints
+
+create database cheatsheet;
+use cheatsheet;
+
+create table Employee (
+    ID int,
+    FirstName varchar(255),
+    LastName varchar(255),
+    Age int
+)
+
+insert into employees values (1, "Vikas", "Ahlawat", 30);
+insert into employees values (2, "nikita", "Jain", 25);
+insert into employees values (3, "Ashish", "Kumar", 32);
+insert into employees values (4, "Nikhil", "Sharma", 27);
+insert into employees values (5, "anish", "kadian", 43);
+
+-- NOT NULL CONSTRAINT
+alter table Employee
+change
+    Age
+    Age int NOT NULL;
+
+--UNIQUE CONSTRAINT
+alter table Employee
+add constraint u_q unique(ID);
+
+alter table Employee
+drop constraint u_q;
+
+--PRIMARY KEY CONSTRAINT
+alter table Employee
+add constraint p_k primary key(ID);
+
+alter table Employee
+drop constraint p_k;
+
+--CHECK CONSTRAINT
+alter table Employee
+add constraint Age check (age>=30);
+
+alter table Employee
+drop check Age;
+
+--DEFAULT CONSTRAINT
+alter table Employee
+alter Age set default 10;
+
+alter table Employee
+alter Age drop default;
+