adding constraints.sql

Author: Shahbaz Khan

Constraints.sql

@@ -0,0 +1,26 @@
+--1.Unique:It ensures that an attribute can't caontain duplicate values
+--2.Not Null: Particular attribute can't be left without value
+/*3.Primary Key: It is both unique as well as not null 
+4.Check: Checks and ensures that input in specific attribute is
+           within  the domain conditions or constraints  specified in
+           check
+        Example-  check(age>10) will ensure that age attribute can
+                    values more than 10 only.
+5. Foreign Key: When primary key of one table is used as a refrence 
+                in another table
+
+               A. Including a foreign key while creating the table */
+               create table course(
+                   cid varchar2(10),
+                   cname varchar2(20),
+                   eid int refrences empl1(roll_no) 
+               )
+            --B.Including a foreign key in already created table
+            alter table course add constraint fk
+            foreign key(eid) refrences empl1(roll_no)
+
+  /*6.Default: It provides default inputs for an attribute if no
+                data is given for that particular attribute
+
+                Example:
+                    salary int dafault 10000