I have a simple code that works as follows. I have a table A and I want to query it and store the result in a new table B. For simplicity assume qty and price are two of the fields of the table A. My simple sql file contains the following and works just fine.
DROP TABLE IF EXISTS B;
CREATE TABLE B AS
SELECT *
FROM A
WHERE A.qty >10
Now I want to dynamically modify the query by representing it as a string variable (say s) and updating the string s on the fly. Suppose the string variable s is originally
s = 'SELECT * FROM A WHERE A.qty>10'
we then update it on the fly by concatenating another string as follows:
s = 'SELECT * FROM A WHERE A.qty>10 AND A.price >30'
I want to execute s as a query and save the results in Table B.
I read dynamic sql related documents of postgresql and not quite sure how to achieve the above goal. I am novice and any help will be greatly appreciated.
You can write a function like this and pass the condition as parameter:
create or replace function add_table_b(s text) returns int as $$
declare
rc int:=0;
query_ text:='';
begin
if(trim(s)= '') then
s='';
else
s=' where '||s;
end if;
DROP TABLE IF EXISTS B;
execute 'CREATE TABLE B AS SELECT * FROM A '|| s;
GET DIAGNOSTICS rc = ROW_COUNT;
return rc;
end;
$$
language plpgsql
this function will return the count of rows inserted in table B.
Related
I need to create a function that will generate a table.
This table will have columns brought with several left joins.
At some point i need to filter the data based on the value of a dynamic column (i need to have: WHERE table_name.dynamic_column_name = 1)(that column has 1s and 0s, i need to keep only the 1s)
So when I 'call' the function, user should type like this: SELECT * FROM function_name(dynamic_column_name)
What i did:
CREATE OR REPLACE FUNCTION check_gap (_col_name varchar)
RETRUNS TABLE ( ... here i have several columns with their type ...)
LANGUAGE plpsql
AS $function$
BEGIN
RETURN QUERY
SELECT ... a bunch of columns ...
FROM ... a bunch of tables left joined ...
WHERE _col_name = 1;
END;
$function$
;
I even tried with table_name._col_name .. though it wasn't necessary, the query (select from) works just as fine without
** I found some solutions for dynamic value but not for a dynamic column
*** I am using PostgreSQL (from DBeaver)
You need dynamic SQL for that. Pls. note that the code below is SQL injection prone.
CREATE OR REPLACE FUNCTION check_gap (col_name varchar)
RETURNS TABLE (... several columns with their type ...) LANGUAGE plpgsql AS
$$
BEGIN
RETURN QUERY EXECUTE format
(
'SELECT ... a bunch of columns ...
FROM ... a bunch of tables left joined ...
WHERE %I = 1;', col_name
);
END;
$$;
I have a function that uses RECORD to temporarily store the data. I can use it - it's fine. My problem is that I can't hardcode columns I need to get from the RECORD. I must do it dynamically. Something line:
DECLARE
r1 RECORD;
r2 RECORD;
BEGIN
for r1 in Select column_name
from columns_to_process
where process_now = True
loop
for r2 in Select *
from my_data_table
where whatever
loop
-----------------------------
here I must call column by its name that is unknown at design time
-----------------------------
... do something with
r2.(r1.column_name)
end loop;
end loop;
END;
Does anyone know how to do it?
best regards
M
There is no need to select the all the qualifying rows and compute the total in a loop. Actually when working with SQL try to drop the word loop for your vocabulary; instead just use sum(column_name) in the select. The issue here is that you do not know what column to sum when the query is written, and all structural components(table names, columns names, operators, etc) must be known before submitting. You cannot use a variable for a structural component - in this case a column name. To do that you must use dynamic sql - i.e. SQL statement built by the process. The following accomplishes that: See example here.
create or replace function sum_something(
the_something text -- column name
, for_id my_table.id%type -- my_table.id
)
returns numeric
language plpgsql
as $$
declare
k_query_base constant text :=
$STMT$ Select sum(%I) from my_table where id = %s; $STMT$;
l_query text;
l_sum numeric;
begin
l_query = format(k_query_base, the_something, for_id);
raise notice E'Rumming Statememt:\n %',l_query; -- for prod raise Log
execute l_query into l_sum;
return l_sum;
end;
$$;
Well, after some time I figured out that I could use temporary table instead of RECORD. Doing so gives me all advantages of using dynamic queries so I can call any column by its name.
DECLARE
_my_var bigint;
BEGIN
create temporary table _my_temp_table as
Select _any, _column, _you, _need
from _my_table
where whatever = something;
execute 'Select ' || _any || ' from _my_temp_table' into _my_var;
... do whatever
END;
However I still believe that there should be a way to call records field by it's name.
I have a trigger function that is called by several tables when COLUMN A is updated, so that COLUMN B can be updated based on value from a different function. (More complicated to explain than it really is). The trigger function takes in col_a and col_b since they are different for the different tables.
IF needs_updated THEN
sql = format('($1).%2$s = dbo.foo(($1).%1$s); ', col_a, col_b);
EXECUTE sql USING NEW;
END IF;
When I try to run the above, the format produces this sql:
($1).NameText = dbo.foo(($1).Name);
When I execute the SQL with the USING I am expecting something like this to happen (which works when executed straight up without dynamic sql):
NEW.NameText = dbo.foo(NEW.Name);
Instead I get:
[42601] ERROR: syntax error at or near "$1"
How can I dynamically update the column on the record/composite type NEW?
This isn't going to work because NEW.NameText = dbo.foo(NEW.Name); isn't a correct sql query. And I cannot think of the way you could dynamically update variable attribute of NEW. My suggestion is to explicitly define behaviour for each of your tables:
IF TG_TABLE_SCHEMA = 'my_schema' THEN
IF TG_TABLE_NAME = 'my_table_1' THEN
NEW.a1 = foo(NEW.b1);
ELSE IF TG_TABLE_NAME = 'my_table_2' THEN
NEW.a2 = foo(NEW.b2);
... etc ...
END IF;
END IF;
First: This is a giant pain in plpgsql. So my best recommendation is to do this in some other PL, such as plpythonu or plperl. Doing this in either of those would be trivial. Even if you don't want to do the whole trigger in another PL, you could still do something like:
v_new RECORD;
BEGIN
v_new := plperl_function(NEW, column_a...)
The key to doing this in plpgsql is creating a CTE that has what you need in it:
c_new_old CONSTANT text := format(
'WITH
NEW AS (SELECT (r).* FROM (SELECT ($1)::%1$s r) s)
, OLD AS (SELECT (r).* FROM (SELECT ($2)::%1$s r) s
'
, TG_RELID::regclass
);
You will also need to define a v_new that is a plain record. You could then do something like:
-- Replace 2nd field in NEW with a new value
sql := c_new_old || $$SELECT row(NEW.a, $3, NEW.c) FROM NEW$$
EXECUTE sql INTO v_new USING NEW, OLD, new_value;
I have this function where I store the result of a query in a RECORD type variable.
The problem is that the two tables of my query have one column with the same name ("description"), and I don't know how I can distinguish these two using my RECORD variable.
CREATE OR REPLACE FUNCTION fn_x(_id BIGINT)
RETURNS TEXT AS $BODY$
DECLARE
l_row RECORD;
l_tableADescription TEXT;
l_tableBDescription TEXT;
BEGIN
SELECT *
INTO l_row
FROM tableA a
JOIN tableB b ON (a.idA = b.idA)
WHERE e.idA = _id;
-- problem is here
l_tableADescription = l_row.tableA.description;
l_tableBDescription = l_row.tableB.description;
-- do other stuff
RETURN '';
END;
$BODY$
LANGUAGE plpgsql STABLE;
Using AS in the SELECT clause is not an option because these two tables have a large number of columns.
I am using PostgreSQL 9.4.4
If the column names are not unique, I don't know of any way around naming the variables when you enter the query. i.e.:
SELECT a.description AS t1Desc, b.description AS t2Desc, *
INTO row
FROM tableA a
JOIN tableB b ON (a.idA = b.idB);
Then to access them individually from the RECORD variable:
tableADescription_1 = row.t1Desc;
tableBDescription_1 = row.t2Desc;
Use the names as specified in the query, not the original column names from the table.
That's what we used in a project where we had two tables in a join with a common name.
Im new to writing stored functions in postgresql and in general . I'm trying to write onw with an input parameter and return a set of results stored in a temporary table.
I do the following in my function .
1) Get a list of all the consumers and store their id's stored in a temp table.
2) Iterate over a particular table and retrieve values corresponding to each value from the above list and store in a temp table.
3)Return the temp table.
Here's the function that I've tried to write by myself ,
create or replace function getPumps(status varchar) returns setof record as $$ (setof record?)
DECLARE
cons_id integer[];
i integer;
temp table tmp_table;--Point B
BEGIN
select consumer_id into cons_id from db_consumer_pump_details;
FOR i in select * from cons_id LOOP
select objectid,pump_id,pump_serial_id,repdate,pumpmake,db_consumer_pump_details.status,db_consumer.consumer_name,db_consumer.wenexa_id,db_consumer.rr_no into tmp_table from db_consumer_pump_details inner join db_consumer on db_consumer.consumer_id=db_consumer_pump_details.consumer_id
where db_consumer_pump_details.consumer_id=i and db_consumer_pump_details.status=$1--Point A
order by db_consumer_pump_details.consumer_id,pump_id,createddate desc limit 2
END LOOP;
return tmp_table
END;
$$
LANGUAGE plpgsql;
However Im not sure about my approach and whether im right at the points A and B as I've marked in the code above.And getting a load of errors while trying to create the temporary table.
EDIT: got the function to work ,but I get the following error when I try to run the function.
ERROR: array value must start with "{" or dimension information
Here's my revised function.
create temp table tmp_table(objectid integer,pump_id integer,pump_serial_id varchar(50),repdate timestamp with time zone,pumpmake varchar(50),status varchar(2),consumer_name varchar(50),wenexa_id varchar(50),rr_no varchar(25));
select consumer_id into cons_id from db_consumer_pump_details;
FOR i in select * from cons_id LOOP
insert into tmp_table
select objectid,pump_id,pump_serial_id,repdate,pumpmake,db_consumer_pump_details.status,db_consumer.consumer_name,db_consumer.wenexa_id,db_consumer.rr_no from db_consumer_pump_details inner join db_consumer on db_consumer.consumer_id=db_consumer_pump_details.consumer_id where db_consumer_pump_details.consumer_id=i and db_consumer_pump_details.status=$1
order by db_consumer_pump_details.consumer_id,pump_id,createddate desc limit 2;
END LOOP;
return query (select * from tmp_table);
drop table tmp_table;
END;
$$
LANGUAGE plpgsql;
AFAIK one can't declare tables as variables in postgres. What you can do is create one in your funcion body and use it thourough (or even outside of function). Beware though as temporary tables aren't dropped until the end of the session or commit.
The way to go is to use RETURN NEXT or RETURN QUERY
As for the function result type I always found RETURNS TABLE to be more readable.
edit:
Your cons_id array is innecessary, just iterate the values returned by select.
Also you can have multiple return query statements in a single function to append result of the query to the result returned by function.
In your case:
CREATE OR REPLACE FUNCTION getPumps(status varchar)
RETURNS TABLE (objectid INTEGER,pump_id INTEGER,pump_serial_id INTEGER....)
AS
$$
BEGIN
FOR i in SELECT consumer_id FROM db_consumer_pump_details LOOP
RETURN QUERY(
SELECT objectid,pump_id,pump_serial_id,repdate,pumpmake,db_consumer_pump_details.status,db_consumer.consumer_name,db_consumer.wenexa_id,db_consumer.rr_no FROM db_consumer_pump_details INNER JOIN db_consumer ON db_consumer.consumer_id=db_consumer_pump_details.consumer_id
WHERE db_consumer_pump_details.consumer_id=i AND db_consumer_pump_details.status=$1
ORDER BY db_consumer_pump_details.consumer_id,pump_id,createddate DESC LIMIT 2
);
END LOOP;
END;
$$
edit2:
You probably want to take a look at this solution for groupwise-k-maximum problem as that's exactly what you're dealing with here.
it might be easier to just return a table (or query)
CREATE FUNCTION extended_sales(p_itemno int)
RETURNS TABLE(quantity int, total numeric) AS $$
BEGIN
RETURN QUERY SELECT quantity, quantity * price FROM sales
WHERE itemno = p_itemno;
END;
$$ LANGUAGE plpgsql;
(copied from postgresql docs)