SQL Exception:can not create table

Question

when i run the code this error follows

Exception in thread "main" java.sql.SQLException: Can't create table 'Sensors_db.one' (errno: 121)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
    at com.mysql.jdbc.PreparedStatement.execute(PreparedStatement.java:1362)
    at sensordev.SensorDev.sensorPage(SensorDev.java:283)
    at sensordev.SensorDev.main(SensorDev.java:893)

following is my my code

String type = "37";
        String senName = "one";
        String query;
        switch(type){
            case "37":{

                query = "CREATE TABLE IF NOT EXISTS `"+ senName +"` ("
                        + "  `Name` VARCHAR(45) NOT NULL,"
                        + "  `State` VARCHAR(45) NOT NULL,"
                        + "  `Time` TIME NOT NULL,"
                        + "  PRIMARY KEY (`Time`, `State`),"
                        + "  INDEX `fk_dummy_1_idx` (`Name` ASC),"
                        + "  CONSTRAINT `fk_dummy_1`"
                        + "    FOREIGN KEY (`Name`)"
                        + "    REFERENCES `Sensors_db`.`sensorInfo` (`SName`)"
                        + "    ON DELETE NO ACTION"
                        + "    ON UPDATE NO ACTION);";
                defaultStmt = conn.prepareStatement(query);
                 defaultStmt.execute();

'conn' is my database instance and 'defaultStmt' is a PreparedStatement

Answer 1

err 121 indicates that the constraint name is already used. Change your constraint name. Constraint name should be unique within your database.

To see if the constraint already exists.

SELECT
    table_name
FROM
    information_schema.table_constraints
WHERE
    constraint_type = 'FOREIGN KEY'
    AND table_schema = DATABASE() AND
    constraint_name = 'fk_dummy_1'