I have a mysql database that I am trying to retrieve from our website host (godaddy). I followed a format that seems to be right but it tells me that:
java.sql.SQLException: No database selected
Code:
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try {
// STEP 2: Register JDBC driver
Class.forName(JDBC_DRIVER);
// STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
// STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql;
sql = "SELECT * FROM item_master";
ResultSet rs = stmt.executeQuery(sql); //<-- This is where the error is.
// STEP 5: Extract data from result set
while (rs.next()) {
// Retrieve by column name
int id = rs.getInt("id");
// Display values
System.out.print("ID: " + id);
}
...
}
I did a print statement of the conn to maybe think the connection could of been null and was shown this:
com.mysql.jdbc.JDBC4Connection#2a6*****
Anyone have any ideas what could cause something like this?
Your URL for your database should include your database name. This is normally your URL followed by a "/DBNAME".
String URL = "jdbc:mysql://localhost:3306/mydb";
Where "mydb" is your database name.
What is the value of DB_URL? As far as I am aware, the URL needs to be of the form:
"WEBURL/DATABASENAME:PORT"
Are you just trying to connect to the WEBURL, without specifying a DATABASE?
I had the same problem.
Just run one more query (before your 'SELECT' statement) to connect to your database.
First:
sql = "USE <yourdatabase>";
ResultSet rs = stmt.executeQuery(sql);
And after:
sql = "SELECT * FROM item_master";
rs = stmt.executeQuery(sql);
Related
I'm trying to programmatically update H2 in memory database in my code. For some strange reason I cannot seem to be able to get the create a schema or table. No errors, it just doesn't seem to work. I can create a table using the method below but not a schema
Statement stmt = null;
Class.forName("org.h2.Driver");
try (Connection conn = DriverManager.getConnection("jdbc:h2:tcp://localhost:9090/mem:test", "sa","")) {
//STEP 3: Execute a query
System.out.println("Creating schema in given database...");
stmt = conn.createStatement();
String sql = "CREATE SCHEMA IF NOT EXISTS TEST";
stmt.executeUpdate(sql);
System.out.println("Created schema in given database...");
stmt.close();
The H2 jdbc url, to my knowledge, should be "jdbc:h2:mem:test". Try with this one. See if it helps.
I need to select rows from mysql table based on various criteria, for example Colour= Black, or size= L.
The code works without the preparedstatement and the question marks, but whenever I attempt to use the question marks the code does not run.
I have read something about typing the question mark like \'?'// but I am not sure about the exact format.
String URL = "jdbc:mysql://localhost:3306/clothing";
String USERNAME = "root";
String PASSWORD = "password";
Connection con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
Statement stmt = con.createStatement();
String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ? AND Size = ?;";
ResultSet rs = stmt.executeQuery(sql);
PreparedStatement preparedStmt = con.prepareStatement(sql);
preparedStmt.setString(1, Data1);
preparedStmt.setString(2, Data2);
Also, Size is written out in orange colour, but the error happens also when I only use this sql String
String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ?;";
I have looked at like 20 different answers, but didnt find anything helpful, so thanks in advance for any help!
You are executing the query using a normal java.sql.Statement, not using a java.sql.PreparedStatement. This won't work because a normal Statement does not support parameterized queries. So, remove the creation and execution of the Statement, and make sure you execute the statement using the PreparedStatement:
String URL = "jdbc:mysql://localhost:3306/clothing";
String USERNAME = "root";
String PASSWORD = "password";
String sql= "SELECT * FROM clothing.Lostandfound WHERE Colour = ? AND Size = ?;";
try (Connection con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
PreparedStatement preparedStmt = con.prepareStatement(sql)) {
preparedStmt.setString(1, Data1);
preparedStmt.setString(2, Data2);
try (ResultSet rs = preparedStmt.executeQuery()) {
// process result set
}
}
Also note the addition of try-with-resources, which will ensure connections, statements and result sets are closed correctly.
In mysql the system variable "max_connections" has value 100.
But i am trying to override this value programatically by pass key-value pair in jdbc connection string
as "jdbc:mysql://localhost/test?maxConnections=3".
But it seems like it is not reflecting any change.
Here below I made maxConnection to 3 but still in below example I am able to create 40 connections.
Note I have not closed connection in each iteration purposely.Just to see if the key value added in jdbc connection string is taking effect.If it takes effect then it should give exception of "Too many Connections"
See below code for reference:
public class JDBCOne {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
for(int i=1;i<=35;i++)
{
Connection conn = null;
Statement stmt = null;
Class.forName("com.mysql.jdbc.Driver");
System.out.println("Connecting to database...:"+i);
conn = DriverManager.getConnection("jdbc:mysql://localhost/test?maxConnections=3", "root", "root");
stmt = conn.createStatement();
Integer id = null;
String name = null;
Double amount = null;
String sql = "SELECT * FROM emp where id=1";
ResultSet rs = stmt.executeQuery(sql);
while (rs.next()) {
id = rs.getInt("id");
name = rs.getString("name");
amount = rs.getDouble("amount");
}
System.out.println("id-" + id);
}
System.out.println("Goodbye!");
}
}
max_connections is a global MySQL server variable governing the number of connections the server accepts from all programs connecting to it.
It's not a configuration string parameter, though. So, if you try to change it with a connection string, You Can't Do That™.
See this. https://dev.mysql.com/doc/connector-j/5.1/en/connector-j-reference-configuration-properties.html
You can set it using set global max_connections = 200; if you have the SUPER privilege.
e.g.:
try (PreparedStatement pstmt = conn.prepareStatement("SET GLOBAL max_connections = ?")) {
pstmt.setInt(1, 200);
pstmt.execute();
} catch (SQLException ex) {
throw new RuntimeException(ex);
}
I can't say for sure, but it may be possible that com.mysql.jdbc.Driver is closing some of the connections when conn and/or stmt go out of scope.
You could try putting them outside the for loop:
Connection conn = null;
Statement stmt = null;
for(int i=1;i<=35;i++)
{
You could verify if connections are staying open by running the following MySQL command:
SHOW PROCESSLIST;
I'm trying to execute multiple sql commands, but it gives me "error in your SQL syntax;"
Db_Connection dbconn = new Db_Connection();
Connection myconnection = dbconn.Connection();
String sqlString = "SELECT DISTINCT std_id FROM std_crs WHERE crs_id ='222123'; "
+ "SELECT * FROM cplus_grades ;";
Statement myStatement = myconnection.createStatement();
boolean results = myStatement.execute(sqlString);
do {
if (results) {
ResultSet rs = myStatement.getResultSet();
while (rs.next()) {
}
rs.close();
}
results = myStatement.getMoreResults();
} while(results);
myStatement.close();
I did a small test with three JDBC drivers:
MS SQL: works, returns two result sets
MySQL: fails with a syntax error - that is what you are seeing
HSQLDB: runs, but returns only one result set.
So I guess it simply depends on the JDBC driver if this technique works. Maybe it works only in MS SQL JDBC.
UPDATE:
It also works with Postgres.
please
1. String dbUrl = "jdbc:mysql://yourDatabase?allowMultiQueries=true";
this should be your jdbc connection url
I am having problem retrieving OUT parameter from mysql stored procedure in java.
CALL proc_after_topic_add('newtest',#result);
SELECT #result;
this query gives me desired out parameter but how would i retrieve it in java.I tried using CallableStatement but i get
java.sql.SQLException: Callable statments not supported.
error.Please guys help me.
I have tried following
String sql = "CALL proc_after_topic_add(?,?);";
CallableStatement cstmt = conn.prepareCall(sql);
cstmt.setString(1, topicname);
cstmt.registerOutParameter(2, java.sql.Types.INTEGER);
ResultSet rs = cstmt.executeQuery();
if (rs.next()) {
if (rs.getInt(1) == 1) {
res = 0;
} else {
res = -1;
}
}
I havent posted stored procedure code because there is nothing wrong with it.
PS:I a using mysql 5.5.21 and yes i should probably mention i am using mysql connector 3.0.15
Okay this is solved.For anyone who encounters the same problem,just download latest version of mysql connector.
Error in this line
cstmt.registerOutParameter(2, java.sql.Types.INTEGER);
change like this
String sql = "CALL proc_after_topic_add(?,?);";
cstmt.registerOutParameter(2, java.sql.Types.INTEGER);
Create a schema test and create a table employee in schema with 2 columns.
id and employeename and insert some data.
Use this Stored Procedure.
DELIMITER $$
DROP PROCEDURE IF EXISTS `test`.`get_count_name1` $$
CREATE PROCEDURE `test`.`get_count_name1`(IN the_name VARCHAR(64),OUT
the_count INT)
BEGIN
SELECT COUNT(*) INTO the_count from employee where employeename=the_name;
END$$
DELIMITER ;
Use this example.
username and password are root and root for me. change as per your
requirement. Here i am counting the occurence of employeename="deepak"
import java.sql.*;
public class JDBCExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/test";
// Database credentials
static final String USER = "root";
static final String PASS = "root";
public static void main(String[] args) {
Connection conn = null;
CallableStatement stmt = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
String sql = "{call get_count_name1 (?, ?)}";
stmt = conn.prepareCall(sql);
//Bind IN parameter first, then bind OUT parameter
String name = "Deepak";
stmt.setString(1, name); // This would set ID as 102
// Because second parameter is OUT so register it
stmt.registerOutParameter(2, java.sql.Types.INTEGER);
//Use execute method to run stored procedure.
System.out.println("Executing stored procedure..." );
stmt.execute();
int count=stmt.getInt(2);
System.out.println(count);
stmt.close();
conn.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}// nothing we can do
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
}//end main
}//end JDBCExample