I´m working for the first time with OCI so this may be a basic question.... I´m coming from MySql word.... Using VS2012 with C++.
I wish to do a simple SELECT statement with some variations on WHERE and LIMIT clause. The SQL query is build dynamically from a C++ written processor and the statement comes ready from this module. So I may have something like:
SELECT * FROM MYTABLE3; or
SELECT F1, F2, F3 FROM MYTABLE1; or even
SELECT F1, F3, F4 FROM MYTABLE2 WHERE ID > 10;
No big deal here.
My problem is that I DON´T KNOW IN ADVANCE THE TABLE FORMAT, so I cannot bind variables to it before executing the statement and fetching the table structure. In MySql that´s easy, because I execute the statement and I get the resultSet. From the resultSet I can check the number of columns retrieved, the name, data format and size of each column. After reading that data I build a dynamic matrix with the table structure and its data, my final goal. Something as:
sql::ResultSetMetaData *resultMeta = resultSet->getMetaData();
while (resultSet->next())
{
for (unsigned int i = 1; i <= resultMeta->getColumnCount(); i++)
{
std::string label = resultMeta->getColumnLabel(i);
std::string type = resultMeta->getColumnTypeName(i);
// ... Get the resultset attributes and data
}
retData.push_back(data);
}
From what I´ve seen in Oracle, I need to bind the variables that are going to be returned before issuing the execute/fetch operations. In my case I cannot do it because I don´t know the table structure in advance...
I´m pretty sure Oracle can do that, I just don´t know how to do it. I´ve read the Oracle Docs and did not find references to it....
Help is very much appreciated and code examples also. I´m stuck with that for 2 days now... Thanks for helping.
Can you please try the following on your statement handle ( stmhp). This will give you column count on your oracle statement.
err = OCIAttrGet ((dvoid *)stmhp, (ub4)OCI_HTYPE_STMT, (dvoid *)
&parmcnt, (ub4 *) 0, (ub4)OCI_ATTR_PARAM_COUNT, errhp);
Please check this link also which will help you to find out data type of every column in the resultset.
Retrieving data type information for columns in an Oracle OCCI ResultSet
Related
I'm using Pentaho PDI 7.1. I'm trying to convert data from Mysql to Mysql changing the structure of data.
I'm reading the source table (customers) and for each row I've to run another query to calculate the balance.
I was trying to use Database value lookup to accomplish it but maybe is not the best way.
I've to run a query like this to get the balance:
SELECT
SUM(
CASE WHEN direzione='ENTRATA' THEN -importo ELSE +importo END
)
FROM Movimento WHERE contoFidelizzato_id = ?
I should set the parameter taking it from the previous step. Some advice?
The Database lookup value may be a good idea, especially if you are used to database reasoning, but it may result in many queries which may not be the most efficient.
A more PDI-ish style would be to make the query like:
SELECT contoFidelizzato_id
, SUM(CASE WHEN direzione='ENTRATA' THEN -importo ELSE +importo END)
FROM Movimento
GROUP BY contoFidelizzato_id
and use it as the info source of a Lookup Stream Step, like this:
An even more PDI-ish style would be to divert the source table (customer) in two flows : one in which you keep the source rows, and one that you group by contoFidelizzato_id. Of course, you need a formula, or a Javascript, or to put a formula in the SQL of the Table input to change the sign when needed.
Test to know which strategy is better in your case. You'll soon discover that the PDI is very good at handling large data.
I have this PostgreSQL PL/pgSQL function:
CREATE OR REPLACE FUNCTION get_people()
RETURNS SETOF people AS $$
BEGIN
RETURN QUERY SELECT * FROM people;
END;
$$ LANGUAGE plpgsql;
Then I try to read the data in an application using SOCI, with this code:
session sql {"postgresql://dbname=postgres"};
row person {};
procedure proc = (sql.prepare << "get_people()", into(person));
proc.execute(true);
I would expect that person have the data of the first person, but it contains only one column with the name of the stored procedure (i.e., "get_people").
So I don't know what I am doing wrong here, or not doing. Is it the PL/pgSQL code or the SOCI code? Maybe SOCI does not support dynamic binding for stored procedures. Also, this method would allow me to read the first row only, but what about the rest of rows? I know SOCI comes with the rowset class for reading result sets, but the documentation says it only works with queries. Please help.
SELECT get_people() will return a single column, of type people, named after the procedure.
SELECT * FROM get_people() will give you the expected behaviour, decomposing the people records into their constituent fields.
Judging from the source, it looks like the SOCI procedure class (or at least, its Postgres implementation) is hard-wired to run procedures as SELECT ... rather than SELECT * FROM ....
I guess this means you'll need to write your own query, i.e.:
statement stmt = (sql.prepare << "SELECT * FROM get_people()", into(person));
I have an array of 128 ints. Which I want as a column in my mysql table. (or if someone has a better Idea that is welcome)
Basically I don't know 2 things:
1) What is the syntax for this process in C++ i.e serializing the data and inserting it into the table.
int x = 1;
int myarray[128];
serialize(myarray);//?
mysql_query(con, "INSERT INTO db VALUES('"x"', myarray)");
//int myarray[128]; also dont know the syntax for the int value insertion.
2) What is the syntax for the table creation process with this serialized data i.e
mysql_query(con, "CREATE TABLE table(Id INT not null, (serialized int array[128]))");
Any help would be greatly appreciated!
My understanding of the MySql INSERT INTO syntax is:
INSERT INTO db
("X")
VALUES ((1), (2), (3));
You don't want to serialize an array for this. You want the textual representation of each value in the array.
I suggest using std::ostringstream and a for loop to build a string containing the textual representations of the array contents.
You could do as I did and search the web for examples of the correct syntax:
Wikipedia - SQL Syntax for INSERT into, including multiple rows
Edit 1:
Also search the web for "MySql Load File":
Google results of "MySql load file"
Alright I am in a rather difficult situation, or at least I think so anyway. I have been doing some research on how to fix my problem but have really come up empty handed.
I need to be able to reindex the rowid of my table after I delete a row. That way at any given time when I want to update or index a row by the rowid it is accessing the correct one.
Now for those of you asking why. Basically I am interfacing a "homebrewed" db that was programmed in C and is really just a bunch of memory locations all accessed like they were a db table. So what I'm trying to say is they can look up a row by searching for a value in the table, or by simply saying i want row 6. Lastly the table could consist of really anything, and any values which means they dont create a column as an index and ultimately the only thing for me to index their row by row number is the rowid to my knowledge.
So I have found that VACUUM would do what I want or need but it appears that the system that database is in isn't giving sqlite privileges to write so when VACUUM is run it comes back with and error. (ERROR 14 or Unable to open the database file) (I also know that my db is open so that isn't the issue but not having write privileges is the only reason I can come up with) I have also read some stuff about the auto increment or something like that but didn't really understand/think that was going to be able to fix my problem.
Any suggestions or ideas from the sqlite or database geniuses out that would be appreciated.
Not sure if I have understood completely your problem, but if you can use SQL code maybe you can write a query to update the IDs (assuming they are in dense order).
You can use a query like this:
UPDATE t1
SET id = (SELECT rank
FROM (SELECT id,
(
SELECT count()+1
FROM (SELECT DISTINCT id
FROM t1 AS t
WHERE t.id < t1.id
)
) rank
FROM t1
) AS sub
WHERE sub.id = t1.id
);
You can check my demo in SQLFiddler. In this demo you will see the result of the DELETE and UPDATE statements (to simulate your case) if you run all queries together.
I have been searching for a while on how to get the generated auto-increment ID from an "INSERT . INTO ... (...) VALUES (...)". Even on stackoverflow, I only find the answer of using a "SELECT LAST_INSERT_ID()" in a subsequent query. I find this solution unsatisfactory for a number of reasons:
1) This will effectively double the queries sent to the database, especially since it is mostly handling inserts.
2) What will happen if more than one thread access the database at the same time? What if more than one application accesses the database at the same time? It seems to me the values are bound to become erroneous.
It's hard for me to believe that the MySQL C++ Connector wouldn't offer the feature that the Java Connector as well as the PHP Connector offer.
An example taken from http://forums.mysql.com/read.php?167,294960,295250
sql::Statement* stmt = conn->createStatement();
sql::ResultSet* res = stmt->executeQuery("SELECT ##identity AS id");
res->next();
my_ulong retVal = res->getInt64("id");
In nutshell, if your ID column is not an auto_increment column then you can as well use
SELECT ##identity AS id
EDIT:
Not sure what do you mean by second query/round trip. First I thought you are trying to know a different way to get the ID of the last inserted row but it looks like you are more interested in knowing whether you can save the round trip or not?
If that's the case, then I am completely agree with #WhozCraig; you can punch in both your queries in a single statement like inser into tab value ....;select last_inserted_id() which will be a single call
OR
you can have stored procedure like below to do the same and save the round trip
create procedure myproc
as
begin
insert into mytab values ...;
select last_inserted_id();
end
Let me know if this is not what you are trying to achieve.