Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to drop constraint on a column of a table in a database using JDBC API?
You can drop a constraint on a column of a table using the ALTER TABLE command.
Syntax
ALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint;
Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:
+--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | UNI | NULL | | | CustomerName | varchar(255) | YES | | NULL | | | DispatchDate | date | YES | | NULL | | | DeliveryTime | time | YES | | NULL | | | Price | int(11) | YES | | NULL | | | Location | text | YES | | NULL | | | ID | int(11) | NO | PRI| NULL | | +--------------+--------------+------+-----+---------+-------+
Following JDBC program establishes connection with MySQL database, and drops a constraint named MyUniqueConstraint from the Sales table.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class DroppingConstraint {
public static void main(String args[]) throws SQLException {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql://localhost/mydatabase";
Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connection established......");
//Creating the Statement
Statement stmt = con.createStatement();
//Query to alter the table
String query = "ALTER TABLE Sales DROP INDEX MyUniqueConstraint";
//Executing the query
stmt.executeUpdate(query);
System.out.println("Constraint dropped......");
}
}Output
Connection established...... Constraint dropped......
Since we dropped UNIQUE constraint named MyUniqueConstraint, (which is on the column ProductName) from the sales table, if you get the description of the Sales table using the describe command you can observe that the Key value UNI added opposite to ProductName, removed.
mysql> describe sales; +--------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName | varchar(255) | YES | | NULL | | | CustomerName | varchar(255) | NO | | NULL | | | DispatchDate | date | YES | | NULL | | | DeliveryTime | time | YES | | NULL | | | Price | int(11) | YES | | NULL | | | Location | text | YES | | NULL | | | ID | int(11) | NO | PRI | NULL | | +--------------+--------------+------+-----+---------+-------+ 7 rows in set (0.00 sec)
Updated on: 30-Jul-2019
227 Views
Advertisements