Java: Cannot use the "USE" keyword from MySQL?

Question

I have two SQL files:

query1.sql

SELECT * FROM laptop_store.gpu;

query2.sql

USE laptop_store;
SELECT * FROM gpu

Excecuting both in MySQL Workbench 8.0 CE will display the same result :

result:

When I copy everything from two SQL code and run it in java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class NewClass {
    static String queryString1 = "SELECT * FROM laptop_store.gpu";

    static String queryString2 = "USE laptop_store;\n" +
                                 "SELECT * FROM gpu";

    public static void main(String[] args) {
       try{      
          Class.forName("com.mysql.cj.jdbc.Driver");  
          Connection con = DriverManager.getConnection( 
              "jdbc:mysql://localhost:3306/laptop_store","root","tomnisa123");          

          Statement statement = con.createStatement();   

          //Change SQL code here:
          ResultSet rs = statement.executeQuery(queryString1); 

          ResultSetMetaData rsmd = rs.getMetaData();

          int colCount = rsmd.getColumnCount();

            while(rs.next()) {
                for (int i = 1; i <= colCount; i++){          
                    System.out.print(rs.getString(i) + "  ");
                }
                System.out.println();
            }

          con.close();  

       } catch(Exception e){ 
        System.out.println(e);
       }  
    }  
}

Only the first one is success

success .

But the second one shows an error:

java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT * FROM gpu' at line 2

Why I cannot use the "USE" keyword from MySQL?

Why do you want to? You're already using the `laptop_store` database, the `USE` line is unnecessary. — T.J. Crowder, May 04 '19 at 10:42
Pretty sure the Java MySQL client functions createStatement and executeQuery does not support multiple SQL statements separated by semicon. — Raymond Nijland, May 04 '19 at 10:48

Stephen C · Accepted Answer · 2019-05-05T05:02:59.343

Apparently, the problem is that you are trying to execute two SQL statements in a single executeQuery call. You can't do that. Run the "use" in a separate execute calls.

But the question is why are you using the use statement?

If you are using it for no particular reasons ... don't.
If you are using it to make sure that you are using the correct database, that is unnecessary. The database / schema to be used is specified in the connection URL.
```
 "jdbc:mysql://localhost:3306/laptop_store"
                              ^^^^^^^^^^^^
```
If you are using it to dynamically switch between databases / schemas, it may be better to use a separate connection for each database.

Java: Cannot use the "USE" keyword from MySQL?

1 Answers1