I have the following query where the first argument itself is a subquery
The java code is:
String query = select * from (?) where ROWNUM < ?
PreparedStatement statement = conn.preparedStatement(query)
statement.setString(1, "select * from foo_table")
statement.setInt(2, 3)
When I run the java code, I get an exception. What alternatives do I have for making the first subquery statement.setString(1, "select * from foo_table") a parameter?
This is not possible, parameter placeholders can only represent values, not object names (like table names, column names, etc) nor subselects or other query elements.
You will need to dynamically create the query to execute using string concatenation, or other string formatting/templating options.
Related
when trying to search with single record then this query works
#Query(value = "select * from table t where t.column1 = :column1 and t.column2 = :column2 and t.column3 = :column3")
Flux<Invoice> findByMultipleColumn(#Param("column1”) String column1, #Param("column2”) String column2, #Param("column3”) String column3);
But when I have list of criterias instead of a single row condition then I have to loop over the list of criterias & call the above query multiple times which is not feasible solution.
Sudo code
for (Criteria criteria : criteriaList) {
repository.findByMultipleColumn(criteria.getColumn1(), criteria.getColumn2(), criteria.getColumn3());
}
What I am trying to find a way to solve the above query for multiple LIST of all the 3 column criteria pair, something like below (this is not working solution)
#Query(value = "select * from table t where t.column1 = :column1 and t.column2 = :column2 and t.column3 = :column3")
Flux<Invoice> findByMultipleColumn(#Param List<Table> table);
Is there any way somehow we can try to achieve the above case?
Would be doable if column1, 2 and 3 were Embedded, then you could do
#Query(select * from Entity where embeddedProperty in (:values))
Flux<Entity> findByEmbeddedPropertyIn(Collection<EmbeddedClas> values);
Which would generate the following native SQL clause
Where (column1, column2, column3) in ((x, y, z), ...)
If you don't want to pack these fields i to an embeddable class, you can also try to do a workaround
#Query(select * from Entity where Concat(column1, ';', column2, ';', column3) in (:parametersConcatrenatedInJava)
Flux<Entity> findBy3Columns(Collection<String> parametersConcatrenatedInJava);
It's ofcourse not bulletproof, all three columns could have ";" as their values, this might be problematic if their type is not string, etc.
Edit.:
Third option is to use specification api. Using the criteria builder you can concatenate multiple and / or queries. And pass that specification as an argument to the repository that extends JpaSpecificationExecutor (if you're fetching whole entities) or an entity manager if you're using projections. Read more about specifications
Main Query:
PreparedStatement pstmt = con.prepareStatement("DELETE FROM employee WHERE eno = 1");
Working: by concatenation
PreparedStatement pstmt = con.prepareStatement("DELETE FROM "+tn+" WHERE "+cn+" = ?");
Not Working: when used positional parameter
PreparedStatement pstmt = con.prepareStatement("DELETE FROM ? WHERE ? = ?");
Can we use positional parameters only for working with table data?
Why I'm not able to work with table_name, column_name etc.?
The point of a prepared statement is to let the database prepare an execution plan (i.e. compute what needs to be done, using which tables, indices, joining strategies, algorithms, etc.), and then to execute that plan one or several times with various parameters.
If the database doesn't even know which table it must delete from, based on which criteria, there's no way it can prepare the execution plan.
I'm trying to implement https://stackoverflow.com/a/16392399/14731 for a table called "Modules" using QueryDSL. Here is my query:
String newName = "MyModule";
QModules modules = QModules.modules;
BooleanExpression moduleNotExists = session.subQuery().
from(modules).where(modules.name.eq(newName)).notExists();
SimpleSubQuery<String> setModuleName = session.subQuery().
where(moduleNotExists).unique(Expressions.constant(newName));
long moduleId = session.insert(modules).set(modules.name, setModuleName).
executeWithKey(modules.id);
I am expecting this to translate into:
insert into modules(name)
select 'MyModule'
where not exists
(select 1 from modules where modules.name = 'MyModule')
Instead, I am getting:
NULL not allowed for column "NAME"; SQL statement:
insert into MODULES (NAME)
values ((select ?
from dual
where not exists (select 1
from MODULES MODULES
where MODULES.NAME = ?)))
where ? is equal to MyModule.
Why does QueryDSL insert from dual? I am expecting it to omit from altogether.
How do I fix this query?
For the insert into select form use
columns(...).select(...)
But your error suggests that the INSERT clause is valid, but semantically not what you want.
Using InsertClause.set(...) you don't get the conditional insertion you are aiming for.
In other words with
columns(...).select(...)
you map the full result set into an INSERT template and no rows will be inserted for empty result sets, but with
set(...)
you map query results to a single column of an INSERT template and null values will be used for empty results.
I'm using JDBC, I have to set array of values to a single column,
I know it works in Hibernate and Ibatis but it seems to be hard to get it working Pure JDBC sql.
I have an array of String values
names[] = new String[]{"A","B","C"};
and a Query like
select * from emp where name in(?)
I tried pstmt.setObject(1,names), it is not working..
This is not supported in pure JDBC. You have to generate a query so that the in clause contains one placeholder for each element of the array.
Spring's JDBC helper classes support named parameters and what you want to do.
This will work with the following Syntax:
"SELECT * FROM emp WHERE name IN ( SELECT column_value FROM TABLE( ? ) )"
pmst.setArray( 1, conn.createArrayOf( "VARCHAR", names ) );
I am trying to refer to a column name to order a query in an application communicating with an Oracle database. I want to use a bind variable so that I can dynamically change what to order the query by.
The problem that I am having is that the database seems to be ignoring the order by column.
Does anyone know if there is a particular way to refer to a database column via a bind variable or if it is even possible?
e.g my query is
SELECT * FROM PERSON ORDER BY :1
(where :1 will be bound to PERSON.NAME)
The query is not returning results in alphabetical order, I am worried that the database is interpreting this as:-
SELECT * FROM PERSON ORDER BY 'PERSON.NAME'
which will obviously not work.
Any suggestions are much appreciated.
No. You cannot use bind variables for table or column names.
This information is needed to create the execution plan. Without knowing what you want to order by, it would be impossible to figure out what index to use, for example.
Instead of bind variables, you have to directly interpolate the column name into the SQL statement when your program creates it. Assuming that you take precautions against SQL injection, there is no downside to that.
Update: If you really wanted to jump through hoops, you could probably do something like
order by decode(?, 'colA', colA, 'colB', colB)
but that is just silly. And slow. Don't.
As you are using JDBC. You can rewrite your code, to something without bind variables. This way you can also dynamically change the order-by e.g.:
String query = "SELECT * FROM PERS ";
if (condition1){
query = query+ " order by name ";
// insert more if/else or case statements
} else {
query = query+ " order by other_column ";
}
Statement select = conn.createStatement();
ResultSet result = select.executeQuery(query);
Or even:
String columnName = getColumnName(input);
Statement select = conn.createStatement();
ResultSet result = select.executeQuery("SELECT * FROM PERS ORDER BY "+columnName);
ResultSet result = select.executeQuery(
"SELECT * FROM PERS ORDER BY " + columnName
);
will always be a new statement to the database.
That means it is, like Thilo already explained, impossible to "reorder" an already bound, calculated, prepared, parsed statement. When using this result set over and over in your application and the only thing, which changes over time is the order of the presentation, try to order the set in your client code.
Otherwise, dynamic SQL is fine, but comes with a huge footprint.