Is there a way to pass an array of strings for a "WHERE country IN (...)" query?
something like this:
String[] countries = {"France", "Switzerland"};
PreparedStatement pstmt = con.prepareStatement("SELECT * FROM table WHERE country IN (?...)");
pstmt.setStringArray(1, countries);
pstmt.executeQuery();
an ugly workaround would be to create the query based on the size of the array
String[] countries = {"France", "Switzerland"};
if (countries.size() == 0) { return null; }
String query = "SELECT * FROM table WHERE country IN (?";
for (int i = 1; i < countries.size; i++) { query += ", ?"; }
PreparedStatement pstmt = con.prepareStatement(query);
for (int i = 0; i < countries.size; i++) { pstmt.setString(1+i, countries[i]); }
pstmt.executeQuery();
but this looks really ugly.
any idea?
No, it's not possible. ORMs like Hibernate or wrapper APIs like Spring JDBC allows doing that. But with plain JDBC, you must do it yourself.
I think the work around would be formulating the entire query string at runtime and using a Statement object instead of PreparedStatement.
No way to try this.See here to other ways.But there is one exception, if you use oracle database then you can try this
If your database engine support IN (subquery), you can create a view or memory table to do it.
Related
Hi I'm using preparedStatement in Java to execute query in DB.
The table:
When it comes to update, delete and insert it's all fine, however when it comes to select( ex. I've done "SELECT ?,?,?,?,? from person" and set strings afterwards) and the following result is returned:
I'm assuming that because it's the strings that are replacing ? so it did not come out as expected:(please correct me if it's wrong)
Expected sql: "SELECT no,name,tel,birthday,address FROM person"
Actual sql: "SELECT \"no\",\"name\",\"birthday\",\"address\" FROM person"
I've tested the second one in in Navicat:
I'd like to understand that why executing this query statement would return a result like this?
If it would help here's Java code:
// Data Assist Object
public class DAO {
static String jdbcurl;
static String username;
static String password;
static{
try {
Class.forName("com.mysql.jdbc.Driver");
ResourceBundle rb = ResourceBundle.getBundle("db");
jdbcurl = rb.getString("jdbcurl");
username = rb.getString("username");
password = rb.getString("password");
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
}
// for insert, delete and update
public int modify(String sql, String[] args){
int x=0;
try(Connection con = DriverManager.getConnection( jdbcurl,username ,password);
PreparedStatement ps = con.prepareStatement(sql);){
for (int i = 0; i < args.length; i++) {
ps.setString(i+1, args[i]);
}
x =ps.executeUpdate();
System.out.println(x);
}catch(SQLException e){
e.printStackTrace();
}
return x;
}
// for select
public List<Map<String,String>> query(String sql, String[] params){
List<Map<String,String>> resList = new ArrayList<>();
try(Connection con = DriverManager.getConnection( jdbcurl,username ,password);
PreparedStatement ps = con.prepareStatement(sql);){
for (int i = 0; i < params.length; i++) {
ps.setString(i+1, params[i]);
}
try(ResultSet res =ps.executeQuery();){
ResultSetMetaData mdata = res.getMetaData();
int num = mdata.getColumnCount();
while(res.next()){
HashMap<String,String> data = new HashMap<>();
for (int i = 1; i <= num; i++) {
String result = res.getString(i);
String columnName = mdata.getColumnName(i);
data.put(columnName,result);
}
resList.add(data);
}
}
}catch(Exception e){
e.printStackTrace();
}
return resList;
}
public static void main(String[] args) throws SQLException {
DAO dao = new DAO();
String sql = "insert into person(name,tel,birthday,address) values(?,?,?,?)";
sql = "select ?,?,?,?,? from person";
List<Map<String,String>> res = dao.query(sql, new String[]{"no","name","tel","birthday","address"});
for(Map m:res){
System.out.print("no: "+m.get("no")+",");
System.out.print("name: "+m.get("name")+",");
System.out.print("tel: "+m.get("tel")+",");
System.out.print("birthday: "+m.get("birthday")+",");
System.out.println("address: "+m.get("address"));
}
}
}
Thanks for any help.
SQL basically works on a show me these columns where this criteria is true basis.
In the statement:
"SELECT \"no\",\"name\",\"birthday\",\"address\" FROM person"
You're getting
SELECT "no", "name", "birthday", "address" FROM person
when it actually hits the database. The "" operator creates a string in SQL. In plain English, that means that you're telling the database to return that specified set of strings for each row in person where the criteria you listed is met.
Since you didn't list a where clause, all rows are true by default so you get one row of strings for every single row in the person table. The first query is the same thing, but instead of directly passing the strings, you're adding them in as bind variables.
If you actually want to see the values in the table, write the query without the "'s
SELECT no, name, birthday, address FROM person
Unless otherwise specified, bind functions generally pass the value as a string. Which is why the query behaved the way it did. I don't recommend using bind variables in the select clause. That's a strange practice.
Edit:
As Adrian pointed out in the comments, " denotes columns in SQL. My apologies for not catching that. I assume that you meant to use the ' operator which actually denotes strings.
If not, something else is going on here entirely.
For the select you use the question marks in the WHERE clause, not where you list the fields you need as output.
Replace
sql = "select ?,?,?,?,? from person";
with
sql = "select no,name,tel,birthday,address from person";
For this particular query there is no binding to do. It will retrieve all the records from the table.
I have following question.
I'm using JDBC in my project and I made simple method to insert data into my database.
My problem is: What to do when I want to insert something like sysdate or just NULL to auto increment? To my method I send only strings and writing NULL to string doesn't work.
Can you give me any advice how to improve it?
This is the code with constant null in query, but it isn't what I want to.
public static void insertInto(String Table, ArrayList<String> values) throws SQLException
{
Connection conn = JavaConnectDB.ConnectDb();
OraclePreparedStatement pst = null;
StringBuilder Query = new StringBuilder("INSERT INTO " + Table + " VALUES (NULL, ");
for (int i = 0; i < values.size(); i++)
{
Query.append("? ");
if (i + 1 != values.size())
Query.append(", ");
}
Query.append(")");
pst = (OraclePreparedStatement) conn.prepareStatement(Query.toString());
for (int i = 0; i < values.size(); i++)
{
pst.setString(i + 1, values.get(i));
}
pst.executeUpdate();
}
This method creates query like "INSERT INTO TABLE VALUES (NULL, ?, ? ,?)" and then fills gaps with values from array.
There is java.sql.PreparedStatement.setNull(int, int)
Try, e.g.
pst.setNull(1, Types.BIGINT);
for (int i = 1; i < values.size(); i++)
{
pst.setString(i + 1, values.get(i));
}
Change Types.BIGINT for apporpriate type for your column.
Note, that values.get(0) is just ignored, but should present in the array.
Problem is the setString function. If you have a string "NULL" or "SYSDATE", it will result in the query being quoted ('NULL', 'SYSDATE'), so this will be inserted as string.
According to this answer, pst.setString(n, null) should do the trick already, so inserting SQL NULL values is yet relatively easy, just insert a Java null value into the array where you want the database value to be SQL NULL.
SYSDATE gets more delicate. But I think, here comes something more fundamental into play: how are you going to handle data types other than VARCHAR (see setString documentation). If you really wanted such a generic method, I would rather to pass ArrayList<Object> as parameter (or with ellipsis ...) and call the appropriate setXXX method for the specific Object type - or setObject with appropriate Type parameter set. You could then create your own class SysDate which could easily be detected.
Is the database layout known to your application? Then I'd rather recommend to have a separate insert method for each table accepting exactly the number of required parameters of correct type, such as
bool insertIntoTest(int someValue, Integer anotherValue, String andAnotherOne)
{
Connection conn = JavaConnectDB.ConnectDb();
OraclePreparedStatement pst
= (OraclePreparedStatement) conn.prepareStatement(
"INSERT INTO TEST (someValue, anotherValue) VALUES(?, ?)"
);
pst.setInt(1, someValue);
if(anotherValue == 0)
pst.setNull(2, Types.INTEGER);
else
pst.setInt(2, anotherValue);
// can handle null already...
pst.setString(3, andAnotherOne);
/* ... (execute, try/catch, return) */
}
Well you should define exactly what do ou want to do.
It's not possible to put null in an autoinkrement field on database by definition
Auto-increment allows a unique number to be generated when a new record is inserted into a table.
So if you want just to insert some filed to your table and delegate the genration of autoincrement to your database, you should create your query like that :
INSERT INTO TABLE VALUES (?, ? ,?).
Example :
Table employee(id,time,name)
Query :
INSERT INTO employee (time, name) VALUES (?, ?)
Is there an efficient way to obtain a list (preferably an array, a ResultSet will do) to SELECT a lot of rows.
For example:
Connection con = DriverManager.getConnection(host,username,password);
String sql = "SELECT * FROM table_name WHERE food = ? AND expiration > ?";
PreparedStatement stmt = con.prepareStatement(sql);
Using the above code, I want to get all the food from a given array that isn't expired.
String[] foodList = {"banana","apple","orange",...}
where the expiration date is a constant date (lets say 3 days ago). However, the way I have it is that the String and PreparedStatement are in a for loop that loop the number of foods in the array to individually check the expiration date. This creates a lot of ResultSets after I execute each individually.
Most SQL Databases support a IN (list) expression. This is roughly equivalent to providing a or expression:
SELECT id FROM table WHERE food IN ('Apple', 'Banana') AND exp < ?
is similar to
SELECT id FROM table WHERE (food = 'Apple' or food = 'Banana') AND exp < ?
In both cases some RDBMS can optimize it.
However first of all there is a limitation in the number of list items you can specify in the IN or number of characters you can use in the statement. So if your list can be variable long you need to be prepared to run multiple statements.
Secondly you cannot* set a array as an argument to a PreparedStatement and expect it to work with IN.
Unfortunately in plain JDBC all you can do is to concatenate a String. This is frowned upon, but there is no good alternative (unless you want to do something like giving the list of foods as a single list and use a "instring" expression).
Make sure to add as many ? (but not too many) as you expect parameters and then set them in the IN:
String[] foods = ...;
int remain = foods.length;
int start = 0;
while(remain > 0)
{ if (remain >= 100)
executeBatch(foods, start, 100); start+=100; remain-=100;
else if (remain >= 30)
executeBatch(foods, start, 30); start+=30; remain-=30;
else {
executeBatch(foods, start, 1); start+=1; remain-=1;
}
}
void executeBatch(String[] f, int off, int len)
{
StringBuilder sqlBuf = StringBuilder("... IN(");
for(int i=0;i<len;i++) {
sqlBuf.append((i!=0)?",?":"?");
}
String sql = sqlBuf.append(") AND exp < ?").toString();
PreparedStatement ps = c.prepareStatement(sql);
for(int i=0;i<foods.length;i++)
ps.setString(i+1, foods[i+off]);
ps.setTimestamp(foods.length+1, now);
....
}
This avoids to generate a lot of different SQL statement to compile. (Only 100,30 or 1 ?)). You can use the same logic for the OR case.
* not to be confused with ARRAY database type.
Probably not the most elegant solution, and you won't get any performance benefit from the prepared statement (but you will get parameter binding):
StringBuilder sql = new StringBuilder("SELECT * FROM table_name WHERE expiration > ? AND food IN (");
for (int i = 0; i < foodList.length; i++) {
if (i > 0) {
sql.append(',');
}
sql.append('?');
}
sql.append(")");
Connection con = DriverManager.getConnection(host, username, password);
PreparedStatement stmt = con.prepareStatement(sql.toString());
stmt.setDate(1, expirationDate);
for (int i = 0; i < foodList.length; i++) {
stmt.setString(i + 2, foodList[i]);
}
ResultSet rs = stmt.executeQuery();
/* ... Do Stuff ... */
How can I use a prepared statement to delete entries from a database? I have found that I must write the following code
String deleteSQL = "DELETE DBUSER WHERE USER_ID = ?
but I want to specify a clause with more than one variable. I have used the AND operator but it doesn't seem to work.
Here is an example if your syntax is not correct..
DELETE DBUSER WHERE USER_ID = ? and USER_NAME = ?;
you can append more conditions in where clause by using more AND ... operators.
OR if you have more than one USER_IDs to delete in a single query..
DELETE DBUSER WHERE USER_ID in (?, ?, ?, ?);
It's must work/ for example
Select from Employee e where e.ID < ? and e.ID >= ? order by e.ID
to set values use this:
int id1 = 1;
int id2 = 10;
preparedStatement.setInt(2, id1);
preparedStatement.setInt(1, id2);
for delete I use this code:
public synchronized boolean deleteNewsById(Integer[] idList)
throws NewsManagerException {
DatabaseConnection connection = pool.getConnection();
StringBuffer buffer = new StringBuffer();
buffer.append("(");
buffer.append(idList[0]);
for (int i = 1; i < idList.length; i++) {
buffer.append(",");
buffer.append(idList[i]);
}
buffer.append(")");
PreparedStatement statement = connection
.getPreparedStatement(DELETE_NEWS_BY_ID + buffer);
}
and sql query looks like this
private static final String DELETE_NEWS_BY_ID = "delete from NEWS where ID in ";
or simple write delete from NEWS where ID in (?,?,?) and set values like in first example
I think the response from Aleksei Bulgak is correct, but to perhaps more straightforwardly word it...you can set your parameters like this:
String stmt = "DELETE DBUSER WHERE USER_ID = ? and (USER_NAME = ? or USER_NAME = ?)";
preparedStatement.setInt(1, firstParam);
preparedStatement.setString(2, secondParam);
preparedStatement.setString(3, thirdParam);
...and for however many parameters(question marks) in your SQL (no matter if you're using IN or whatever you want), you should set that many parameters here(using setInt for ints, setString for Strings, etc). This goes for select and delete queries.
Are you looking for the IN operator which allows you to specify multiple values in the WHERE clause such as in my example.
String deleteSQL = "DELETE DBUSER WHERE USER_ID IN (?)"
Though in PreparedStatement IN clause alternatives there are some useful answers and links that you may want to take a look at such as Batch Statements in JDBC which discuss the pros and cons of different batching approaches. The IN approach I'm suggesting is part of that discussion. The end result is that you make just one trip to the database, rather than one per delete and that's better performing because of the reduced network activity required.
I want to do batch query DB for high performance, example sql to query based on different customer_id:
select order_id,
cost
from customer c
join order o using(id)
where c.id = ...
order by
I'm not sure how to do it using JDBC statement. I know I can use stored procedure for this purpose, but it's much better if I can just write sql in Java app instead of SP.
I'm using DBCP for my Java client and MySQL DB.
The JDBC Specification 4.0 describes a mechanism for batch updates. As such, the batch features in JDBC can be used for insert or update purposes. This is described in chapter 14 of the specification.
AFAIK there is not a mechanism for select batches, probably because there is no apparent need for that since, as others have recommended, you can simply retrieve all the rows that you want at once by properly constructing your query.
int[] ids = { 1, 2, 3, 4 };
StringBuilder sql = new StringBuilder();
sql.append("select jedi_name from jedi where id in(");
for (int i = 0; i < ids.length; i++) {
sql.append("?");
if(i+1 < ids.length){
sql.append(",");
}
}
sql.append(")");
System.out.println(sql.toString());
try (Connection con = DriverManager.getConnection(...)) {
PreparedStatement stm = con.prepareStatement(sql.toString());
for(int i=0; i < ids.length; i++){
stm.setInt(i+1, ids[i]);
}
ResultSet rs = stm.executeQuery();
while (rs.next()) {
System.out.println(rs.getString("jedi_name"));
}
} catch (SQLException e) {
e.printStackTrace();
}
Output
select jedi_name from jedi where id in(?,?,?,?)
Luke, Obiwan, Yoda, Mace Windu
Is there any reason why you would consider that you need a thing like a batch-select statement?
It is really does not matter what is your SQL statement (you can use as many nested joins as your DB can handle). Below is basic Java example (not DBCP). For DBCP example which is pretty similar you can check out their example.
Connection connect = DriverManager.getConnection(YOUR_CONNECTION_STRING);
// Statements allow to issue SQL queries to the database
Statement statement = connect.createStatement();
ResultSet resultSet = statement.executeQuery("select order_id, cost
from customer c
join order o using(id)
where c.id = ...
order by");