I am trying to figure out how to write a trigger function in PL/pgSQL that can select values into host variables in an Embedded SQL/C program. I am new to SQL, so I apologize if my terminology is a bit off. Basically, on a change to the table, I want the function to trigger a view in order to update the values stored in host variables.
This is the view I have created and tested to work:
EXEC SQL CREATE VIEW idfound AS SELECT id, num FROM newtable WHERE id = 1;
This is how I have called the view, using host variables dbID and dbNum:
EXEC SQL SELECT * INTO :dbID, :dbNum FROM idfound;
Here is the trigger I have created:
EXEC SQL CREATE idTrigger AFTER INSERT OR UPDATE ON newtable
FOR EACH ROW EXECUTE PROCEDURE idFunc();
And here is the trigger function I would like to use:
EXEC SQL CREATE FUNCTION idFunc() RETURNS TRIGGER AS $idTrigger$
BEGIN
SELECT * INTO :dbID, :dbNum FROM idfound;
END;
$idTrigger$ LANGUAGE plpgsql;
For testing purposes, I am using pgAdmin III. When I change the function to perform any action that doesn't use the host variables (such as update a value in a predefined row), I can see that it is created. However, I am unable to get it to create the trigger or trigger function using the host variables.
Right now, I am just trying to figure out how to achieve this in general, so I am aware that my current code doesn't actually do much. The general idea is that I want my trigger function to call a predefined view that uses host variables in C. If there is a better way of implementing the trigger, that advice would be greatly appreciated as well.
Trigger functions are executed in the server environment and cannot access the memory space of the client environment, neither for reading nor writing. That's a fundamental point of the client-server architecture, so there's no workaround, this is just not possible.
The closer workable equivalent may be for the trigger to NOTIFY and for the client to LISTEN and consume the notifications and the associated payload.
Related
I am new at programming with delphi. I am currently creating a simple notebook program and i need some help. I have a form called contacts with 5 tEdit fields. I am thinking i could create a stored procedure in my sybase database to insert record into Contacts table, so I can call it with my delphi programm. How do I call this procedure in delphi? the values that will be inserted should be taken from users input into these tEdit fields. Anyone has any suggestions? Or am I thinking the wrong way? thanks in advance
You have several options here, and it will depend on what VCL controls you are using.
(1). You can insert via a tTable component. This let's you have a quick, easy, low level control. You drop the component on the form, set the component properties (tablename, etc), then something like
MyTable.Open;
MyTable.Insert; (or maybe append)
MyTable.FieldByName('MY_FIELD').AsString := 'Bob'; // set the field values
MyTable.post;
(2). Use SQL. Drop a SQL component on the form. Set the SQLText property, using parameters;
for example : "Insert into table (MyField) values :X". My opinion is that this is easier to do in complex situations, correlated subselects, etc.
MySQL.Close;
MySQL.ParamByName('X').AsString := 'BOB';
ExecSQL;
(3). Use stored procedures. - The advantage to this is that they are useable by multiple applications, and can be changed easily. If you want to update the SQL code, you update it once (in the database), versus having to change it in an app, and then distribute the app to multiple users.
The code for this will be nearly identify to (2), although I don't know the specifics of your VCL library. In effect though, you will specify the routine to run, specify the parameter values, and then execute the stored procedure.
Note that all these routines will return an error code or exception code. It is best practice to always check for that...
Here is a little more complex example, using a SQL statement called qLoader. qLoader exists on a datamodule. I am passing a parameter, executing the SQL statement, then iterating through all the results.
try
with dmXLate.qLoader do
begin
Close;
ParamByName('DBTYPE').AsString := DBType;
Open;
while not dmXLate.qLoader.Eof do
begin
// Here is where we process each result
UserName:= dmXLate.qLoader.FieldByName('USERNAME').AsString;
dmXLate.qLoader.Next;
end;
end;
except
on E: Exception do
begin
ShowMEssage(E.Message);
exit;
end;
end;
Is there a way to update another database with the newly created stored procedure whenever a stored procedure is created in the main database?
For example, i have two databases, DB1 and DB2.
When I create a stored procedure in DB1, i want that same procedure to created in DB2 automatically? Is there a trigger that can do this?
USE [DB1]
CREATE PROCEDURE [dbo].[TestSproc]
..something
AS
BEGIN
...something
END
I know a use [DB2] statement will do the job, but i want this to be done automatically. Any thought?
Thanks for the help!
This might be a bit evil, but in SQL Server you are able to create DDL triggers which fire when you create/alter/drop tables/procedures etc. The syntax to fire when a procedure is created is:
CREATE TRIGGER <proc-name>
ON DATABASE
FOR CREATE_PROCEDURE
AS
--Your code goes here
In a DDL trigger you get access to an object called EVENTDATA. So to get the text of the procedure you created:
SELECT EVENTDATA().value('(/EVENT_INSTANCE/TSQLCommand/CommandText)[1]','nvarchar(max)')
Now all you need to do is keep that value and execute it in your secondary database. So your query becomes something like this, though I leave the code to update the secondary database down to you as I don't know if it's on the same server, linked server etc.:
CREATE TRIGGER sproc_copy
ON DATABASE
FOR CREATE_PROCEDURE
AS
DECLARE #procedureDDL AS NVARCHAR(MAX) = EVENTDATA().value('(/EVENT_INSTANCE/TSQLCommand/CommandText)[1]','nvarchar(max)')
--Do something with #procedureDDL
As this is not tested, there's probably a few gotchas. For example, what happens if you create procedure with full name (CREATE PROC server.database.schema.proc)
No simple solution for this unless you want to execute the same statement twice, once on each target database,
One thing that comes to my mind is that you can Set up Replication and only publish Stored Procedures to your second database which will be the subscriber in this case.
Following is the window where you select which Objects you want to send over to your secondary databases.
I need to make for my webApp a trigger to execute a stored procedure on Oracle. But i'm very new to Oracle and I'm still getting the hang of it. I can make a simple Trigger with a sequence to auto-increment a value from a table, but that's it.
Is there any good tutorials and examples available on this specific subject? I tried searching here, but i have only found a very generic question: How can i learn Stored Procedure and Trigger?. But i can be more specific: I need this trigger to run a stored procedure that generates a new code for my user, adding data to this code. The procedure is done, i just don't know how to use it in a trigger, pass the parameters, and how to insert/update values from the oracle trigger itself.
Help will be much appreciated.
Assuming your function to generate the code is named f_generate_code() and your table is named foobar and the column that should be populated is name code you'd do it like this:
create or replace trigger trg_update_code
before insert or update on foobar
for each row
begin
:new.code := f_generate_code();
end;
/
I have to execute a loop in database. This is only a one time requirement.
After executing the function, I am dropping the function now.
Is there any good approach for creating temporary / disposable functions?
I needed to know how to do a many time use in a script I was writing. Turns out you can create a temporary function using the pg_temp schema. This is a schema that is created on demand for your connection and is where temporary tables are stored. When your connection is closed or expires this schema is dropped. Turns out if you create a function on this schema, the schema will be created automatically. Therefore,
create function pg_temp.testfunc() returns text as
$$ select 'hello'::text $$ language sql;
will be a function that will stick around as long as your connection sticks around. No need to call a drop command.
A couple of additional notes to the smart trick in #crowmagnumb's answer:
The function must be schema-qualified at all times, even if pg_temp is in the search_path (like it is by default), according to Tom Lane to prevent Trojan horses:
CREATE FUNCTION pg_temp.f_inc(int)
RETURNS int AS 'SELECT $1 + 1' LANGUAGE sql IMMUTABLE;
SELECT pg_temp.f_inc(42);
f_inc
-----
43
A function created in the temporary schema is only visible inside the same session (just like temp tables). It's invisible to all other sessions (even for the same role). You could access the function as a different role in the same session after SET ROLE.
You could even create a functional index based on this "temp" function:
CREATE INDEX foo_idx ON tbl (pg_temp.f_inc(id));
Thereby creating a plain index using a temporary function on a non-temp table. Such an index would be visible to all sessions but still only valid for the creating session. The query planner will not use a functional index, where the expression is not repeated in the query. Still a bit of a dirty trick. It will be dropped automatically when the session is closed - as a depending object. Feels like this should not be allowed at all ...
If you just need to execute a function repeatedly and all you need is SQL, consider a prepared statement instead. It acts much like a temporary SQL function that dies at the end of the session. Not the same thing, though, and can only be used by itself with EXECUTE, not nested inside another query. Example:
PREPARE upd_tbl AS
UPDATE tbl t SET set_name = $2 WHERE tbl_id = $1;
Call:
EXECUTE upd_tbl(123, 'foo_name');
Details:
Split given string and prepare case statement
If you are using version 9.0, you can do this with the new DO statement:
http://www.postgresql.org/docs/current/static/sql-do.html
With previous versions, you'll need to create the function, call it, and drop it again.
For ad hock procedures, cursors aren't too bad. They are too inefficient for productino use however.
They will let you easily loop on sql results in the db.
can we create user define function with in stored procedure then end of the store procedure we need to delete that custom user define function.
You can but it could get messy.
Look at sp_executesql. This will allow you to run arbitrary SQL, including DDL. Creating and using UDF's in this way does seem a bit dangerous -- you'll need to make sure that there aren't any name conflicts with competing threads, and there's no way to get any kind of query optimization.
I'd double check your design to make sure there isn't another solution to this!
Dynamic SQL is the only way.
ALTER PROC ...
AS
...
EXEC ('CREATE FUNCTION tempFunc...')
...
EXEC ('DROP FUNCTION tempFunc')
...
GO
However:
if you have 2 concurrent executions it will fail because tempFunc already exists
if each udf definition is different, then you need random names
if you randomise the name, the rest of the code will have to be dynamic SQL too
a stored proc implies reuse so just persist it
your code will need ddl_admin or db_owner rights to create the udf
...
So... why do you want to do this?