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Make Unique Column in Database Table

In this section you will learn, how to define a unique key in a column of a database table.

Make Unique Column in Database Table

Make Unique Column in Database Table

     

In this section you will learn, how to define a unique key in a column of a database table. While declaring unique key in a column we should check whether this column is eligible to store a unique values or not because if the column has been declared as unique then it can't store a duplicate values.  If we ever try to insert the duplicate data in the unique column then it will show an error message to you that you are trying to insert the duplicate value. 

Description of program:

After making a connection with the database firstly compile this program, only after that it will run,  Now give the table name and column name to which you want to make a unique column.  After assigning the unique key to a column the SQL statement is executed with the help of some java methods. If column name becomes unique then shows "Query OK, n rows affected." otherwise, displays a message "Table or column is not found!".

Description of code:

ALTER TABLE  table_name   ADD   UNIQUE(col_name):;
Above code is used to make unique of any column . It takes table name and column name.

Here is the code of program:

import java.io.*;
import java.sql.*;

public class MakeUniqueColumn{
  public static void main(String[] args) {
  System.out.println("Make unique column example!");
  Connection con = null;
  try{
  Class.forName("com.mysql.jdbc.Driver");
  con = DriverManager.getConnection
("jdbc:mysql://localhost:3306/jdbctutorial","root","root");
  try{
  Statement st = con.createStatement();
  BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
  System.out.println("Enter table name: ");
  String table = bf.readLine();
  System.out.println("Enter column name that you want to unique values: ");
  String col = bf.readLine();
  int n = st.executeUpdate("ALTER TABLE "+table+" ADD UNIQUE"+"("+col+")");
  System.out.println("Query OK, "+n+" rows affected.");
  }
  catch (SQLException s){
  System.out.println("Table or column is not found!");
  }
  }
  catch (Exception e){
  e.printStackTrace();
  }
  }
} 

Database Table: Student Table

Stu_id Stu_name Stu_sub Stu_marks
100 vinod computer NULL
101 raju math NULL
102 ranjan bio NULL
103 Aman phy NULL

Output of program:

C:\vinod\jdbc\jdbc\jdbc-mysql>javac MakeUniqueColumn.java

C:\vinod\jdbc\jdbc\jdbc-mysql>java MakeUniqueColumn
Make unique column example!
Enter table name:
Student
Enter column name that you want to unique values:
Stu_id
Query OK, 4 rows affected.

Make unique values: Student Table

Stu_id Stu_name Stu_sub Stu_marks
100 vinod computer NULL
101 raju math NULL
102 ranjan bio NULL
103 Aman phy NULL

Download this example.

Tutorials

  1. Change Column Name in MySQL
  2. Java Mysql Connection Example
  3. JDBC Example with MySQL
  4. Jdbc Mysql Connection String
  5. Jdbc Mysql Connection Url
  6. Getting Column Names from a database table in Java
  7. Count Rows from a Database Table
  8. JDBC Example with MySQL
  9. Write Text File to Table
  10. Inserting Image in Database Table
  11. Insert Data in Table Using Stored Procedure
  12. Copy One Database Table to Another
  13. Copy Table in a MySQL Database
  14. Set Timestamp by using the Prepared Statement
  15. Set Time by using the Prepared Statement
  16. Set Date by using the Prepared Statement
  17. Prepared Statement Set Big Decimal
  18. Set byte, short and long data types by using the Prepared Statement
  19. Set Data Types by using Prepared Statement
  20. Using the Prepared Statement Twice
  21. Deleting Records using the Prepared Statement
  22. Count Records using the Prepared Statement
  23. Inserting Records using the Prepared Statement
  24. Update Records using Prepared Statement
  25. Select Records Using Prepared Statement
  26. Prepared Statement With Batch Update
  27. Statement Batch Update
  28. Prepared Statement Set Object
  29. Cross Join Tables in a Specific Database
  30. Join tables with the NATURAL RIGHT JOIN operation
  31. Join tables with the NATURAL LEFT JOIN operation
  32. Join tables in the specific database
  33. Delete a Column from a Database Table
  34. Delete a Specific Row from a Database Table
  35. Deleting All Rows from a Database Table
  36. Sum of Column in a Database Table
  37. Arrange a Column of Database Table
  38. Arrange a Column of Database Table
  39. Remove Unique Column in Database Table
  40. Make Unique Column in Database Table