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Java DatabaseMetaData supportsUnion() method with example.
The SQL UNION clause/operator is used to combine the results of two or more SELECT statements without returning any duplicate rows.
To use this UNION clause, each SELECT statement must have
- The same number of columns selected
- The same number of column expressions
- The same data type and
- Have them in the same order
But they need not have to be in the same length.
The basic syntax of a UNION clause is as follows −
Syntax
SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition] UNION SELECT column1 [, column2 ] FROM table1 [, table2 ] [WHERE condition]
The supportsUnion() method of the DatabaseMetaData interface is used to determine whether the underlying database supports SQL UNION clause/operator.
This method returns a boolean value which is −
- True, when the underlying database supports SQL UNION clause/operator.
- False, when the underlying database doesn't support SQL UNION clause/operator.
To determine whether the underlying database supports SQL GROUP BY clause −
- Make sure your database is up and running.
- Register the driver using the registerDriver() method of the DriverManager class. Pass an object of the driver class corresponding to the underlying database.
- Get the connection object using the getConnection() method of the DriverManager class. Pass the URL the database and, user name, password of a user in the database, as String variables.
- Get the DatabaseMetaData object with respect to the current connection using the getMetaData() method of the Connection interface.
- Finally, invoke the supportsUnion() method of the ResultSetMetaData interface and save the value it returns in a boolean variable say, bool. If this value is true, underlying database supports SQL UNION clause/operator else it doesn't.
Following JDBC program establishes connection with MySQL database, and determines and prints whether it supports SQL UNION clause/operator.
Example
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.DriverManager;
import java.sql.SQLException;
public class DatabaseMetadata_supportsUnion {
public static void main(String args[]) throws SQLException {
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String url = "jdbc:mysql://localhost/mydatabase";
Connection con = DriverManager.getConnection(url, "root", "password");
System.out.println("Connection established......");
//Retrieving the meta data object
DatabaseMetaData metaData = con.getMetaData();
//Determining whether the underlying database supports SQL UNION clause
boolean bool = metaData.supportsUnion();
if(bool) {
System.out.println("Underlying database supports SQL UNION clause");
} else {
System.out.println("Underlying database doesnot support SQL UNION clause");
}
}
}Output
Connection established...... Underlying database supports SQL UNION clause
Updated on: 30-Jul-2019
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