I'm trying to understand how to deal with procedures in Postgresql.
I get the idea of creating a function that returns a variable. What I don't get is how I can use such variable, for instance, in an insert.
Imagine this, I have a function called getName(), that returns a variable $name$.
What I want is to insert such variable in another table... How can I do this?
If the function returns a single value, you can use it anywhere a constant could be used.
insert into some_table (id, name)
values (42, get_name());
this is the same as using a built-in function:
insert into some_table (id, modified_at)
values (42, now());
It can be used the same way in an update statement
update some_table
set name = get_name()
where id = 42;
Related
In a plpgsql function I need to do several checks, and return some values based on those checks.
I can perform a SELECT INTO v_variable column FROM table but what I need to store is not the result of a SELECT rather a result of an UPDATE table SET column = new_value RETURNING check
Is there a way to store this check in a variable to later us it, or just an OUT variable so this value is returned by the function?
You can store the value from the RETURNING clause in a variable using INTO, just as for SELECT:
UPDATE table
SET column = new_value
RETURNING check INTO my_variable
It doesn't matter if it SELECT, INSERT or UPDATE. When you specify RETURNING it works the same way as it was SELECT. So you can write:
UPDATE table SET column = new_value RETURNING check INTO <your_variable>
More to that, you can use the results in the same query with the help of CTE:
WITH updated AS (
UPDATE table SET column = new_value RETURNING check
)
SELECT check FROM updated ...
I have written a PL/PGSQL function that returns a trigger, so I can call it before each row insert. I realize now that I would also like that function to return the ID of the newly inserted row. I'm not quite sure how to proceed since my function must return a trigger. Here's some code:
CREATE OR REPLACE FUNCTION f_insert_album() RETURNS TRIGGER AS $$
DECLARE
subj_album_id INTEGER;
BEGIN
-- ... some parts where left out
INSERT INTO t_albums_subjective (user_id, album_id, format_id, location_id, rating)
VALUES (NEW.user_id, obj_album_id, NEW.format_id, NEW.location_id, NEW.rating)
RETURNING id INTO subj_album_id;
RETURN NEW;
END;
$$ LANGUAGE plpgsql;
-- Bind insert function to trigger
DROP TRIGGER IF EXISTS tr_v_albums_insert ON v_albums;
CREATE TRIGGER tr_v_albums_insert INSTEAD OF INSERT ON v_albums
FOR EACH ROW EXECUTE PROCEDURE f_insert_album();
I must keep the return type of my function f_insert_album() to TRIGGER, but I would really like to also return the value in subj_album_id, corresponding to the id of the newly inserted row.
Is there anyway to do this? Is it even possible? Obviously changing the return type didn't work with Postgres. Could you suggest an alternative approach if any?
The crucial question: where to return the ID to?
Assuming you want to return it from the INSERT statement directly, then you are almost there. You already assign the newly generated ID to a function parameter:
...
RETURNING id INTO subj_album_id;
Instead, assign it to a column of the row firing the trigger. The special variable NEW holds this row in a trigger function:
...
RETURNING id INTO NEW.album_id; -- use actual column name in view
Then use the RETURNING clause of the INSERT statement:
INSERT INTO v_albums (user_id, format_id, location_id, rating)
VALUES ( ... )
RETURNING album_id;
Obviously, this is only possible if there is a visible column in the view. It does not have to be assigned in the INSERT command, though. The type of the NEW row variable is defined by the definition of the view, not by the INSERT at hand.
Closely related:
RETURNING data from updatable view not working?
For what you seem to be doing (grant access to certain rows of a table to a certain role) row level security (RLS) in Postgres 9.5 or later might be a more convenient alternative:
CREATE POLICY in the manual
The Postgres Wiki: "What's new in PostgreSQL 9.5"
Review by Depesz
I thought immutable strict ment the database could not be modified.
The following inserts a new row in 'some_table':
CREATE FUNCTION insert_row() RETURNS void AS
$$
plv8.execute('INSERT INTO some_table (number) VALUES ($1)', [123]);
$$
LANGUAGE plv8 IMMUTABLE STRICT;
Is it not possible to prevent a function modifying the database?
This works as expected for me.
If I execute something like:
select insert_row() from some_OTHER_table;
I get EXACTLY one new row in some_table regardless of the number of rows in some_other_table.
If you don't want your function modifies your database, simply DON'T put insert or update statements in it.
I am attempting to allow insert statements with a returning clause into a view in Postgres v9.4, but am struggling with the syntax. This is how I want to call the insert statement:
CREATE VIEW MyView AS SELECT a.*, b.someCol1
FROM tableA a JOIN tableB b USING(aPrimaryKey);
INSERT INTO MyView (time, someCol) VALUES (someTime, someValue) RETURNING *;
INSERT INTO MyView (someCol) VALUES (someValue) RETURNING *;
Note that the default for time is NOW(). This is what I have so far:
CREATE RULE MyRuleName AS ON INSERT TO MyView DO INSTEAD (
INSERT INTO tableA (time) VALUES COALESCE(NEW.time, NOW());
INSERT INTO tableB (aPrimaryKey, someCol)
VALUES (CURRVAL('tableA_aPrimaryKey_seq'), NEW.someValue);
);
The above works to insert the value, but I am struggling to try and figure out how to add the returning statement. I have tried the following without success:
CREATE RULE MyRuleName AS ON INSERT TO MyView DO INSTEAD (
INSERT INTO tableA (time) VALUES COALESCE(NEW.time, NOW())
RETURNING *, NEW.someValue;
INSERT INTO tableB (aPrimaryKey, someCol)
VALUES (CURRVAL('tableA_aPrimaryKey_seq'), NEW.someValue);
);
-- ERROR: invalid reference to FROM-clause entry for table "new"
CREATE RULE MyRuleName AS ON INSERT TO MyView DO INSTEAD (
WITH a AS (INSERT INTO tableA (time)
VALUES COALESCE(NEW.time, NOW()) RETURNING *)
INSERT INTO tableB (aPrimaryKey, someCol)
SELECT aPrimaryKey, NEW.someValue FROM a RETURNING *;
);
-- ERROR: cannot refer to NEW within WITH query
Argh! Does anyone know of a way to add a returning statement that gets the primary key (SERIAL) and time (TIMESTAMP WITH TIME ZONE) added to the database in the first insert, along with the value of someCol in the second insert? Thanks!
You are much better off using an INSTEAD OF INSERT trigger here:
CREATE FUNCTION MyFuncName() RETURNS trigger AS $$
DECLARE
id integer;
BEGIN
INSERT INTO tableA (time) VALUES COALESCE(NEW.time, NOW()) RETURNING aPrimaryKey INTO id;
INSERT INTO tableB (aPrimaryKey, someCol1) VALUES (id, NEW.someValue);
RETURN NEW;
END; $$ LANGUAGE PLPGSQL;
CREATE TRIGGER MyView_on_insert INSTEAD OF INSERT ON MyView
FOR EACH ROW EXECUTE PROCEDURE MyFuncName();
Checking the current value of a sequence to see what was inserted in another table is bad bad bad practice. Even while you are here in a single transaction, don't do it.
You are confused about the issue of RETURNING information, because I am confused too when I read your question. Inside of a function use the INTO clause to populate locally declared variables to hold record values which you can then use in subsequent statements. Outside of a function, use the RETURNING clause as you do in your top-most code snippet.
I don't agree with the the hint ("use triggers instead of rules"), because triggers don't allow RETURNING. As written in the Postgresql docu it is a little bit tedious to write the right return list. If you keep the following in mind, it works:
You can only use columns from the original table to form a list which returns columns for the view (!). This means that you have to repeat the view expressions including all subqueries. (using WHERE instead of JOIN ... ON). Additionally you have to replace the NEW table by the original table name.
I have a table in for which I have provided default values for some of its columns. I want to create a function with arguments corresponding to the columns that will insert a record in the table after modifying any null value to the column's default value.I dont want to programmatically construct the query based on which arguments are null. Essentially I would like something like
INSERT into Table (c1, c2, c3, c4)
Values (coalesce(somevar, DEFAULT(c1)), ...)
Is this possible? I ve seen that mysql can do this. Does postgres offer anything similar?
I am using version 9.1
UPDATE: This question provides some interesting solution but unfortunately the results are always text. I would like to get the default value as its true datatype so that I can use it for inserting it. I have tried to find a solution that will cast the default value from text to its datatype (which is provided as text) but I can't find a way:
SELECT column_name, column_default, data_type
FROM information_schema.columns
WHERE (table_schema, table_name) = ('public', 'mytable')
AND column_name = 'mycolumn'
ORDER BY ordinal_position;
The above returns the column_default and data_type as text so how can I cast the column_default to the value of data_type? If I could do this, then my problem would be solved.
If the table definition accepts an INSERT with the default values for all columns, the two-steps method below may work:
CREATE FUNCTION insert_func(c1 typename, c2 typename, ...)
RETURNS VOID AS $$
DECLARE
r record;
BEGIN
INSERT into the_table default values returning *,ctid INTO r;
UPDATE the_table set
col1=coalesce(c1,r.col1),
col2=coalesce(c2,r.col2),
...
WHERE the_table.ctid=r.ctid;
END;
$$ language plpgsql;
The trick is to get all the default values into the r record variable while inserting and use them subsequently in an UPDATE to replace any non-default value. ctid is a pseudo-column that designates the internal unique ID of the row that has just been inserted.
Caveat: this method won't work if some columns have a default null value AND a non-null check (or any check that implies that the default value is not accepted), since the first INSERT would fail.
I ve worked around my problem with a solution similar to Daniel's by creating a temp table with LIKE and INCLUDING DEFAULTS clauses in order to match my rowtype, then i use
INSERT INTO temp_table (c1, c2, ...) VALUES(x1, DEFAULT, ..)
using the default keyword for whatever column i am interested in. Then I insert to the real table by selecting from the temporary and using
VALUES( x1, coalesce(x2, temp_table.c2), ...).
I dont like it, but it works ok: I can select which on which columns I would like to do this "null-replace-with-default" check and it could work for many rows with one pass if I overload my function to accept a record array.