Thread: plpgsql - Insert from a record variable?
Dear Postgresql experts, I'm writing a simple plpgsql function that selects a row from a table, modifies it slightly, and inserts the modified version. This sounds simple, but I can't find how to do the insert in a simple generic fashion: although SELECT has a formthat puts the result in a record variable, INSERT doesn't seem to have anything similar. What I'd like to be able to write is something like this: DECLARE R RECORD; BEGIN SELECT * INTO R FROM TABLE WHERE id=n; R.something := x; INSERT INTO TABLE R; END But as far as I can see the only syntax that is allowed for INSERT is the normal INSERT INTO TABLE (x,y,z) VALUES (a,b,c). To achieve what I want to do I'd need to iterate over the fields of the record (how?) and build up the string ofthe INSERT query. It seems odd that SELECT can use a record variable but INSERT can't, so I wonder if I have missed something. Any suggestions? Thanks in advance for any help anyone can offer. Regards, --Phil.
--- Phil Endecott <__> wrote: > Dear Postgresql experts, > > I'm writing a simple plpgsql function that selects a row from a > table, modifies it slightly, and inserts the modified version. This > sounds simple, but I can't find how to do the insert in a simple > generic fashion: although SELECT has a form that puts the result in a > record variable, INSERT doesn't seem to have anything similar. > > What I'd like to be able to write is something like this: > > DECLARE > R RECORD; > BEGIN > SELECT * INTO R FROM TABLE WHERE id=n; > R.something := x; > INSERT INTO TABLE R; > END I'm not sure if it will work, but have you tried either two of these forms? -- declare r record; begin select * into r from table where id = n; r.something := x; insert into table select r; end; -- declare r record; begin select * into r from table where id = n; r.something := x; insert into table select r.*; end; > > But as far as I can see the only syntax that is allowed for INSERT is > the normal INSERT INTO TABLE (x,y,z) VALUES (a,b,c). To achieve what > I want to do I'd need to iterate over the fields of the record (how?) > and build up the string of the INSERT query. > > It seems odd that SELECT can use a record variable but INSERT can't, > so I wonder if I have missed something. Any suggestions? > > Thanks in advance for any help anyone can offer. > > Regards, > > --Phil. > > ---------------------------(end of > broadcast)--------------------------- > TIP 7: don't forget to increase your free space map settings regards, ===== Riccardo G. Facchini
"Riccardo G. Facchini" <abief_ag_-postgresql@yahoo.com> writes:
> --- Phil Endecott <__> wrote:
>> I'm writing a simple plpgsql function that selects a row from a
>> table, modifies it slightly, and inserts the modified version. This
>> sounds simple, but I can't find how to do the insert in a simple
>> generic fashion: although SELECT has a form that puts the result in a
>> record variable, INSERT doesn't seem to have anything similar.
> I'm not sure if it will work, but have you tried [snip]
> declare r record;
> insert into table select r.*;
I don't know of any way to handle this in existing releases ---
plpgsql's support for rowtype variables is just too limited.
However, in 7.5 you will be able to do either of
insert into table select r.*;insert into table values(r.*);
so long as r is declared to be of a named rowtype (not just RECORD;
that doesn't have a known field list to plan the query with). For
instance I was just experimenting with this test case:
create or replace function fooey(int) returns void as '
declare r foo;
begin select * into r from foo where id = $1; r.f1 = ''baz''; insert into foo select r.*; return;
end' language plpgsql;
regards, tom lane
Phil> Insert from a record variable? Riccardo> Try insert into table select r.*; Tom> in 7.5 Tom> insert into table select r.*; Tom> insert into table values(r.*); Tom> so long as r is declared to be of a named rowtype (not just Tom> RECORD) Thanks! Unfortunately I need record, rather than %rowtype. See my later email where I describe how I am trying to use thiswith inheritance; the function looks up a row in a base table, finds the derived table in which it really exists usingpg_class.relname, and then inserts a modified copy of the row in the derived table. I'm not concerned about the performance issues to do with pre-planning the queries. I think what I really need is an introspectionmechanism so that I can loop over each element of the record and construct the insert as a string. Maybe thisis possible using a different server-side language? I've just had an idea: perhaps rather than inspecting the recordvariable to see what fields it contains, I can look at the table to see what columns it contains (since this amountsto the same thing). Presumably I can do this using information_schema.columns. I'll have a go. --Phil.
I wrote:
> perhaps rather than inspecting the record variable to see what fields
> it contains, I can look at the table to see what columns it contains
This is my effort. It doesn't work, because I can only EXECUTE
SQL statements, not PLPGSQL statements. I need to EXECUTE an
assignment statement to accumulate the string of column values.
I have a feeling that I can EXECUTE a CREATE FUNCTION statement,
and then call the function, but this seems over-the-top. I just
want to insert a record into a table! Any better ideas?
-- Simply insert record r into table t.
-- Doesn't work, because EXECUTE takes an SQL command, not
-- a plpgsql statement.
create function insert_record ( record, text ) as '
-- probably ought to pass schema as well as table name, since
-- information_schema.columns query doesn't use search_path.
declare r as alias for $1; t as alias for $2;
cr information_schema.columns%rowtype; first boolean; column_names text; column_values text;
begin
first := true; for cr in select * from information_schema.columns where table_name=t loop if not first
then column_names := column_names || '', ''; column_values := column_values || '', ''; first := false; end
if; column_names := column_names || quote_ident(cr.column_name);
!! execute ''column_values :=
!! column_values || quote_literal(r.'' || cr.column_name || '')''; end loop;
execute ''insert into '' || t || ''('' || column_names || '') values ('' || column_values || '')'';
end;
' language plpgsql;
--Phil.
Phil Endecott wrote:> !! execute ''column_values :=> !! column_values || quote_literal(r.'' || cr.column_name || '')''; I'm guessing you want something like FOR rec IN EXECUTE ''select column_values || quote_literal(r.'' || cr.column_name || '') alias column_values''; LOOP column_values:= rec.column_values; END LOOP; another suggestion, rather than do> if not first then> column_names := column_names || '', '';> column_values:= column_values || '', '';> first := false;> end if; why not use two arrays and append the name/values using array_append() and use array_to_string() to join them after that? -- basic
"Phil Endecott" <spam_from_postgresql_sql@chezphil.org> writes:
> I think what I really need is an introspection mechanism
> so that I can loop over each element of the record and construct the
> insert as a string. Maybe this is possible using a different
> server-side language?
pltcl can probably handle this; I'm less sure about plperl or plpython.
(No reflection on the languages, but pltcl has the most complete
Postgres interface.)
regards, tom lane
Phil> execute ''column_values := Phil> column_values || quote_literal(r.'' || cr.column_name || '')''; basic> FOR rec IN EXECUTE basic> ''select column_values || quote_literal(r.'' || basic> cr.column_name || '') alias column_values''; LOOP basic> column_values := rec.column_values; basic> END LOOP; I think your code will try to execute a query like this: select column_values || quote_literal(r.something) alias column_values This will fail because column_values and r are both plpgsql variables, and so are not visible to the SQL interpreter. Any other suggestions? --Phil.