I have an update statement with returning statement.
What I want is to put the result into a variable or temp table.
update my_table
set something = 'x'
where id ...
returning *;
I tried to that using the execute statement and e.g. returning row_to_json(my_table.*) but the variable, off cause, only contains the first row returned from the update.
Use a CTE with the UPDATE-RETURNING statement in it, then use that in the INSERT:
CREATE TEMP TABLE t (i int, j int);
CREATE TEMP TABLE u (i int, j int);
INSERT INTO u VALUES (1, 1), (2, 2), (3, 3);
WITH updated AS (
UPDATE u
SET i = i * 10
WHERE i < 3
RETURNING *
)
INSERT INTO t
SELECT *
FROM updated;
SQLFiddle
Related
I have set of queries which are getting repeated in update query for db2
I need to get rid of these getting repeated
So what best I can do. Cte is not working in update query in db2.
Not able to find solution. For select query cte is working but not for update
You may use so called "SELECT from data-change-table-reference" Db2 functionality using CTE.
CREATE TABLE MYTAB (ID INT, DATA INT);
INSERT INTO MYTAB (ID, DATA) VALUES (1, NULL);
WITH
UPD (ID, DATA) AS (VALUES (1, 1), (2, 2))
SELECT COUNT (1)
FROM NEW TABLE
(
UPDATE MYTAB T
SET DATA = U.DATA
FROM UPD U
WHERE T.ID = U.ID
);
SELECT * FROM MYTAB;
ID
DATA
1
1
fiddle
I have a table called Foos where each record references another record in table Bars.
When I attempt to insert a new record with bar_id = x into Foo:
If the count of existing Foos with bar_id = x is > 2, cancel the insert.
Else: insert the new record.
I am trying to get this done in one PostgreSQL query, if possible.
Here is my first attempt that doesn't work:
WITH c AS (SELECT COUNT(*) FROM foos WHERE bar_id = 3),
INSERT INTO foos(bar_id, title) VALUES(3, "Some thing") WHERE c < 2
Insert from a subquery that returns rows only if there are less than 2 like rows:
insert into foos(bar_id, title)
select *
from (select 3, 'Some thing') x
where (select count(*) from foos where bar_id = 3) < 2
Apologies if my question seems to be naive:
I cannot get my head around the 2 statements below, can someone please explain the difference:
OUTPUT $ACTION, INSERTED.BuildRequestID, ..... and
PRINT ##ROWCOUNT
Apparently, they both can be used to print something on the window, with output in the example above, the records that have been inserted will be displayed. And, PRINT ##ROWCOUNT returns the number of rows affected by the last executed statement in the batch, so, if the function was insert, then it will show the inserted records?
Thank you,
In its simplest terms, OUTPUT will give you the actual records affected by a DML statement (INSERT, UPDATE, DELETE, MERGE), ##ROWCOUNT will just tell you how many rows were affected by the previous Statement (not limited to DML).
This is probably easiest understood with a working example that you can run yourself and see both in action:
IF OBJECT_ID(N'tempdb..#T', 'U') IS NOT NULL
DROP TABLE #T;
-- CHECK ##ROWCOUNT
DECLARE #RowCountFromDropTable INT = ##ROWCOUNT;
-- CREATE A TABLE
CREATE TABLE #T (ID INT NOT NULL PRIMARY KEY, Col CHAR(1) NOT NULL);
-- INSERT SOME VALUES AND CHECK THE OUTPUT
INSERT #T (ID, Col)
OUTPUT inserted.*
VALUES (1, 'A'), (2, 'B'), (3, 'C');
-- CHECK ##ROWCOUNT
DECLARE #RowCountFromInsert INT = ##ROWCOUNT;
-- DELETE A VALUE AND INSPECT THE DELETED RECORD WITH OUTPUT
DELETE #T
OUTPUT deleted.*
WHERE ID = 3;
-- CHECK ##ROWCOUNT
DECLARE #RowCountFromDelete INT = ##ROWCOUNT;
-- UPDATE A RECORD AND VIEW BEFORE AND AFTER VALUES
UPDATE #T
SET Col = 'X'
OUTPUT inserted.ID AS ID,
inserted.Col AS UpdatedTo,
deleted.Col AS UpdatedFrom
WHERE ID = 2;
-- CHECK ##ROWCOUNT
DECLARE #RowCountFromUpdate INT = ##ROWCOUNT;
-- USE MERGE, AND CAPTURE ACTION:
MERGE #T AS t
USING (VALUES (2, 'B'), (3, 'C')) AS s (ID, Col)
ON s.ID = t.ID
WHEN NOT MATCHED THEN INSERT (ID, Col) VALUES (s.ID, s.Col)
WHEN MATCHED THEN UPDATE SET Col = s.Col
WHEN NOT MATCHED BY SOURCE THEN DELETE
OUTPUT $Action AS DMLAction,
inserted.ID AS InsertedID,
inserted.Col AS InsertedCol,
deleted.ID AS DeletedID,
deleted.Col AS DeletedCol;
-- CHECK ##ROWCOUNT
DECLARE #RowCountFromMerge INT = ##ROWCOUNT;
SELECT RowCountFromDropTable = #RowCountFromDropTable,
RowCountFromInsert = #RowCountFromInsert,
RowCountFromDelete = #RowCountFromDelete,
RowCountFromUpdate = #RowCountFromUpdate,
RowCountFromMerge = #RowCountFromMerge;
The recordsets output from each of the DML are:
INSERT
ID Col
-------
1 A
2 B
3 C
DELETE
ID Col
-------
3 C
UPDATE
ID UpdatedTo UpdatedFrom
---------------------------
2 X B
MERGE
DMLAction InsertedID InsertedCol DeletedID DeletedCol
------------------------------------------------------------
INSERT 3 C NULL NULL
DELETE NULL NULL 1 A
UPDATE 2 B 2 X
INSPECT ##ROWCOUNTS
RowCountFromDropTable RowCountFromInsert RowCountFromUpdate RowCountFromMerge
--------------------------------------------------------------------------------
0 3 1 3
A quick point on some wording in the qeustion too: You cannot use OUTPUT directly to print something to the window, it returns records much like a SELECT statement. ##ROWCOUNT can be used like any scalar function, so you could use this in consecutive statements. So you could do something like this:
SELECT TOP (1) *
FROM (VALUES (1), (2), (3)) AS t (ID);
SELECT TOP (##ROWCOUNT + 1) *
FROM (VALUES (1), (2), (3)) AS t (ID);
SELECT TOP (##ROWCOUNT + 1) *
FROM (VALUES (1), (2), (3)) AS t (ID);
Which returns 1, 1,2 and 1,2,3 respectively. I have no idea why you would want to do this, but it demonstrates the scope of ##ROWCOUNT a bit better than the above, and how it can be used elsewhere.
How to construct an INSERT statement so that it would not generate the error "insert or update on table ... violates foreign key constraint" in case if the foreign key value does not exist in the reference table?
I just need no record created in this case and success response.
Thank you
Use a query as the source for the INSERT statement:
insert into the_table (id, some_data, some_fk_column
select *
from (
values (42, 'foobar', 100)
) as x(id, some_data, some_fk_column)
where exists (select *
from referenced_table rt
where rt.primary_key_column = x.some_fk_column);
This can also be extended to a multi-row insert:
insert into the_table (id, some_data, some_fk_column
select *
from (
values
(42, 'foobar', 100),
(24, 'barfoo', 101)
) as x(id, some_data, some_fk_column)
where exists (select *
from referenced_table rt
where rt.primary_key_column = x.some_fk_column);
You didn't show us your table definitions so I had to make up the table and column names. You will have to translate that to your names.
You could create a function with plpgsql, which inserts a row and catches the exception:
CREATE FUNCTION customInsert(int,varchar) RETURNS VOID
AS $$
BEGIN
INSERT INTO foo VALUES ($1,$2);
EXCEPTION
WHEN foreign_key_violation THEN --do nothing
END;
$$ LANGUAGE plpgsql
You can then call this function by this:
SELECT customInsert(1,'hello');
This function tries to insert the given parameters into the table foo and catches the foreign_key_violation error if occurs.
Of course you can generalise the function more, to be able to insert in more than one table, but your question sounded like this was only needed for one specific table.
I would like to INSERT only if table exists.
Pseudocode
IF EXISTS TABLE file_headers(
INSERT INTO file_headers
(measurement_id, file_header_index_start, file_header_index_end)
VALUES (1, 1, 100);
INSERT INTO file_headers
(measurement_id, file_header_index_start, file_header_index_end)
VALUES (1, 2, 100);
... -- many INSERTs into same table
);
How can you insert only if the table exists in PostgreSQL?
do $$begin
if exists (select * from pg_catalog.pg_tables where tablename = 'mytable') then
insert into mytable (col1) values (1);
end if;
end$$;
This test would make sense if you wanted to pass table names to a function for dynamic execution.
There is a built-in solution for that: if you want to make sure the table exists, cast it to regclass (or use a regclass parameter to your function to begin with). That verifies existence and escapes possible non-standard syntax at the same time:
How to check if a table exists in a given schema
Table name as a PostgreSQL function parameter