i am using jsp page and i can easily done simple select query but as i am new bee i don't know how to write a query ..in which i am on the basis of selected check box i want to show sorted data ...for that i write following code
java.sql.ResultSet rs;
out.println(sort.toString());
StringBuffer myquery=new StringBuffer("select * from message");
if(count != 0)
{
myquery.append(" ORDER BY ");
myquery.append(sort);
}
rs=stmt.executeQuery(myquery.toString());
in above..sort is the String that is contain column field on which i wnat to sort...but it is giving me sql query statment error how can i solve or rewrite statements..
Related
I'm using knex (+ objection) to generate a HAVING LIKE query. I am adding the below to my query:
/*
This is the shape of queryString and valuesObject
queryString: ' :property0: like :value0',
valuesObject: {
value0: '%7963e2e2-3b5c-499d-bf42-f9b14ea804f8%',
property0: 'logTypeId'
}
*/
// This is where I add them to the query builder
query.having(raw(queryString, valuesObject));
If the ID isn't matched by any rows then nothing is returned as expected, however if id matches one then all rows are being returned.
The start of the query builder looks like this:
const query = Account.query()
.select('prospect:audit.logTypeId as logTypeId')
.where('trident_account.id', accountId)
.first()
.withGraphFetched('[prospect.[audit.[logType, actionBy]]]')
.joinRelated('prospect.[audit]')
.limit(limit)
.offset(offset);
What could be causing this? I have an identical setup on other queries that give the desired result (filter by ID)
When I execute a SQL query from Java and store the boolean returned, the query always returns true which shouldn't be the case at all. So I emptied the table and fired the query again, and yet it returns true for the emptied table. I have attached a picture of the table. I want the query to return true or false, so I can store it in Java. Can someone please specify an alternate code for this, please?
This is my code on java for the query.
boolean avail = st.execute("SELECT EXISTS(SELECT * from sales WHERE product='"+n+"' AND ord_date='"+sqlDate+"');");
And this is my code for result set
Statement st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
This is the table, name of the table is 'sales'
I'm new to MySQL, a more specific approach is appreciated.
Statement.execute will return true regardless of what the query returns. You are still supposed to retrieve the actual result of the query.
Returns
true if the first result is a ResultSet object; false if it is an update count or there are no results
As you execute an EXISTS statement, there will always be a result (true or false). The actual value still has to be retrieved:
You must then use the methods getResultSet or getUpdateCount to retrieve the result, and getMoreResults to move to any subsequent result(s).
For reference: https://docs.oracle.com/javase/8/docs/api/java/sql/Statement.html#execute-java.lang.String-String
Also note that you are directly embedding strings into your query, this will leave you vulnerable to SQL injections. Please read: How can prepared statements protect from SQL injection attacks?. Recommended reading: Introduction to JDBC
The return value of Statement.execute() signals whether the query produces a result set (true) or - possibly - an update count (false). The query you execute is a select which will always produce a result set (even if empty). In other words, it will always return true for a select.
If you want to get the result of your query, then the recommend approach is to use executeQuery. However, you are also concatenating values into your query string, which is a bad idea because it leave you vulnerable to SQL injection. The recommended approach is to switch to prepared statements:
try (PreparedStatement pstmt = con.prepareStatement(
"SELECT EXISTS(SELECT * from sales WHERE product = ? AND ord_date = ?)")) {
pstmt.setString(1, n);
pstmt.setDate(2, sqlDate);
try (ResultSet rs = st.executeQuery() {
boolean avail = rs.next() && rs.getBoolean(1);
// use avail...
}
}
I want to get multiple columns from database in a single query and set it to the corresponding DTO object fields.
Error message:
java.lang.IllegalStateException: No data type for node:
org.hibernate.hql.internal.ast.tree.IdentNode
+-[IDENT] IdentNode: 'payment' {originalText=payment}
Query:
TypedQuery<Object[]> query = entityManager.createQuery("SELECT
payment, createdOn,responseMessage FROM PaymentLog log WHERE log.id
=:personId", Object[].class);
query.setParameter("personId",new BigInteger(basicEntityDto.getId()));
List<Object[]> results = query.getResultList();
for (Object[] log : results) {
paymentTransaction.setAmount(log[0].toString());
paymentTransaction.setDate(log[1].toString());
paymentTransaction.setDescription(log[2].toString());
transactionList.add(paymentTransaction);
}
P.S. I know I can use JPA constructor expression. But as I have to add the DTOs in a list of DTO(i.e. transactionList), so is there a way with JPA construction expression where I can do that by running the query only one time instead in a loop for every single DTO?
You can have the JPA provider transform the result set for you by means of a constructor expression:
http://www.objectdb.com/java/jpa/query/jpql/select#Result_Classes_Constructor_Expressions_
https://en.wikibooks.org/wiki/Java_Persistence/JPQL#Constructors
This requires that the specified class has a constructor matching the select expression. This would then look something like the below:
TypedQuery<PaymentTransaction> query = entityManager.createQuery("SELECT new PaymentTransaction (log.payment, log.createdOn, log.responseMessage ) FROM PaymentLog log WHERE log.id
=:personId", PaymentTransaction.class);
query.setParameter("personId",new BigInteger(basicEntityDto.getId()));
List<PaymentTransaction> results = query.getResultList();
In JPA 2.1 you can also so like the below:
https://en.wikibooks.org/wiki/Java_Persistence/Querying#ConstructorResult_.28JPA_2.1.29
What you could do is:
TypedQuery<PaymentLog> query = entityManager.createQuery("SELECT log FROM PaymentLog log WHERE log.id =:personId", PaymentLog.class);
query.setParameter("personId",new BigInteger(basicEntityDto.getId()));
List<PaymentLog> results = query.getResultList();
for (PaymentLog log : results) {
paymentTransaction.setAmount(log.getPayment());
paymentTransaction.setDate(log.getCreatedOn());
paymentTransaction.setDescription(log.getResponseMessage());
transactionList.add(paymentTransaction);
}
It is not a good idea to select everything from the database if you are not going to use it. If the selected fields were the only columns in the table then approach above works.
If you had a lot more columns in the table, the previous would still work, but this might be better:
TypedQuery<PaymentTransaction> query = entityManager.createQuery("SELECT new PaymentTransaction (log.payment, log.createdOn, log.responseMessage) FROM PaymentLog log WHERE log.id =:personId", PaymentTransaction.class);
query.setParameter("personId",new BigInteger(basicEntityDto.getId()));
List<PaymentTransaction> results = query.getResultList();
The above query will return an already created list of PaymentTransactions. You have to note that the class PaymentTransactionshould have a constructor that accept these fields in the given order. Otherwise it will cause an exception
Hi i have this managed bean where it makes MySQL queries, the problem here is the SQL statement makes a '=' condition instead of 'LIKE'
Here is the code in my managed bean.
Connection con = ds.getConnection();
try{
if (con == null) {
throw new SQLException("Can't get database connection");
}
}
finally {
PreparedStatement ps = con.prepareStatement(
"SELECT * FROM Clients WHERE Machine LIKE '53'");
//get customer data from database
ResultSet result = ps.executeQuery();
con.close();
List list;
list = new ArrayList();
while (result.next()) {
Customer cust = new Customer();
cust.setMachine(result.getLong("Machine"));
cust.setCompany(result.getString("Company"));
cust.setContact(result.getString("Contact"));
cust.setPhone(result.getLong("Phone"));
cust.setEmail(result.getString("Email"));
//store all data into a List
list.add(cust);
}
return list;
Here the SELECT command does not pull all the numbers in 'Machine' column which is like 53, but if i enter a whole value, such as the complete number (53544) in place of 53 then the result is pulled up. I am confused !!
Also if i replace the above select statement with SELECT * FROM Clients the entire database is stored in list. Any ideas ?
Use wildcards:
Like '%53%'
...means everything that contains '53'.
Like '%53' - it ends with 53
LIKE '53%' - it starts with 53
You can also use _ if You want to replace a single character.
You can find a descriptipn HERE
You sql query should be
"SELECT * FROM Clients WHERE Machine LIKE '%53%'
I've stumbled upon a very strange LINQ to SQL behaviour / bug, that I just can't understand.
Let's take the following tables as an example: Customers -> Orders -> Details.
Each table is a subtable of the previous table, with a regular Primary-Foreign key relationship (1 to many).
If I execute the follow query:
var q = from c in context.Customers
select (c.Orders.FirstOrDefault() ?? new Order()).Details.Count();
Then I get an exception: Could not format node 'Value' for execution as SQL.
But the following queries do not throw an exception:
var q = from c in context.Customers
select (c.Orders.FirstOrDefault() ?? new Order()).OrderDateTime;
var q = from c in context.Customers
select (new Order()).Details.Count();
If I change my primary query as follows, I don't get an exception:
var q = from r in context.Customers.ToList()
select (c.Orders.FirstOrDefault() ?? new Order()).Details.Count();
Now I could understand that the last query works, because of the following logic:
Since there is no mapping of "new Order()" to SQL (I'm guessing here), I need to work on a local list instead.
But what I can't understand is why do the other two queries work?!?
I could potentially accept working with the "local" version of context.Customers.ToList(), but how to speed up the query?
For instance in the last query example, I'm pretty sure that each select will cause a new SQL query to be executed to retrieve the Orders. Now I could avoid lazy loading by using DataLoadOptions, but then I would be retrieving thousands of Order rows for no reason what so ever (I only need the first row)...
If I could execute the entire query in one SQL statement as I would like (my first query example), then the SQL engine itself would be smart enough to only retrieve one Order row for each Customer...
Is there perhaps a way to rewrite my original query in such a way that it will work as intended and be executed in one swoop by the SQL server?
EDIT:
(longer answer for Arturo)
The queries I provided are purely for example purposes. I know they are pointless in their own right, I just wanted to show a simplistic example.
The reason your example works is because you have avoided using "new Order()" all together. If I slightly modify your query to still use it, then I still get an exception:
var results = from e in (from c in db.Customers
select new { c.CustomerID, FirstOrder = c.Orders.FirstOrDefault() })
select new { e.CustomerID, Count = (e.FirstOrder != null ? e.FirstOrder : new Order()).Details().Count() }
Although this time the exception is slightly different - Could not format node 'ClientQuery' for execution as SQL.
If I use the ?? syntax instead of (x ? y : z) in that query, I get the same exception as I originaly got.
In my real-life query I don't need Count(), I need to select a couple of properties from the last table (which in my previous examples would be Details). Essentially I need to merge values of all the rows in each table. Inorder to give a more hefty example I'll first have to restate my tabels:
Models -> ModelCategoryVariations <- CategoryVariations -> CategoryVariationItems -> ModelModuleCategoryVariationItemAmounts -> ModelModuleCategoryVariationItemAmountValueChanges
The -> sign represents a 1 -> many relationship. Do notice that there is one sign that is the other way round...
My real query would go something like this:
var q = from m in context.Models
from mcv in m.ModelCategoryVariations
... // select some more tables
select new
{
ModelId = m.Id,
ModelName = m.Name,
CategoryVariationName = mcv.CategoryVariation.Name,
..., // values from other tables
Categories = (from cvi in mcv.CategoryVariation.CategoryVariationItems
let mmcvia = cvi.ModelModuleCategoryVariationItemAmounts.SingleOrDefault(mmcvia2 => mmcvia2.ModelModuleId == m.ModelModuleId) ?? new ModelModuleCategoryVariationItemAmount()
select new
{
cvi.Id,
Amount = (mmcvia.ModelModuleCategoryVariationItemAmountValueChanges.FirstOrDefault() ?? new ModelModuleCategoryVariationItemAmountValueChange()).Amount
... // select some more properties
}
}
This query blows up at the line let mmcvia =.
If I recall correctly, by using let mmcvia = new ModelModuleCategoryVariationItemAmount(), the query would blow up at the next ?? operand, which is at Amount =.
If I start the query with from m in context.Models.ToList() then everything works...
Why are you looking into only the individual count without selecting anything related to the customer.
You can do the following.
var results = from e in
(from c in db.Customers
select new { c.CustomerID, FirstOrder = c.Orders.FirstOrDefault() })
select new { e.CustomerID, DetailCount = e.FirstOrder != null ? e.FirstOrder.Details.Count() : 0 };
EDIT:
OK, I think you are over complicating your query.
The problem is that you are using the new WhateverObject() in your query, T-SQL doesnt know anyting about that; T-SQL knows about records in your hard drive, your are throwing something that doesn't exist. Only C# knows about that. DON'T USE new IN YOUR QUERIES OTHER THAN IN THE OUTER MOST SELECT STATEMENT because that is what C# will receive, and C# knows about creating new instances of objects.
Of course is going to work if you use ToList() method, but performance is affected because now you have your application host and sql server working together to give you the results and it might take many calls to your database instead of one.
Try this instead:
Categories = (from cvi in mcv.CategoryVariation.CategoryVariationItems
let mmcvia =
cvi.ModelModuleCategoryVariationItemAmounts.SingleOrDefault(
mmcvia2 => mmcvia2.ModelModuleId == m.ModelModuleId)
select new
{
cvi.Id,
Amount = mmcvia != null ?
(mmcvia.ModelModuleCategoryVariationItemAmountValueChanges.Select(
x => x.Amount).FirstOrDefault() : 0
... // select some more properties
}
Using the Select() method allows you to get the first Amount or its default value. I used "0" as an example only, I dont know what is your default value for Amount.