I have one table USER and some other tables like USER_DETAILS ,USER_QUALIFICATION etc USER_ID references to all such table i want to remove those USER_ID which are not present in any other tables.
Deleting all of the users that are not present in a connected table:
DELETE FROM table WHERE user_id NOT IN (SELECT user_id FROM other_table)
If you want to delete only users that are not found in any table than you can add
AND NOT IN (SELECT user_id FROM another_table)
Alternatively you can create a tmp table and merge in all the user_ids that you want to keep and use that table in the sub-select for the NOT IN.
Use a DELETE with a not exists condition for all related tables:
delete from "USER" u
where not exists (select *
from user_details ud
where ud.user_id = u.user_id)
and not exists (select *
from user_qualification uq
where uq.user_id = u.user_id);
Note that user is a reserved word, and thus needs to be quoted to be usable as a table name. But quoting makes it case-sensitive. So "USER" and "user" are two different table names. As you have not included the DDL for your tables I cannot tell if your table is named "USER" or "user".
In general I would strongly recommend to avoid using double quotes for identifies completely.
Related
In my current project, a have a few cases where, within data pump operations, I have to execute queries like this (it's not a real example, but it should give you some idea):
DELETE FROM notification
WHERE user_id NOT IN (SELECT id FROM user)
On big tables, such construction performs poorly, I believe it's because of NOT IN construction, which makes it impossible to use indexes.
Such approach should perform better:
DELETE FROM notification
USING (
SELECT n.user_id, u.id FROM notification
LEFT OUTER JOIN user u ON n.user_id = u.id
) i
WHERE
notification.user_id = i.user_id
AND i.id IS NULL
... but it looks a bit overcomplicated.
Is there a better way / best practice for such operations?
We can use EXISTS instead:
DELETE FROM notification
WHERE NOT EXISTS
(SELECT id FROM user WHERE id = notification.user_id)
I'd use NOT EXISTS.
DELETE FROM notification n
WHERE NOT EXISTS (SELECT *
FROM "user" u
WHERE u.id = n.user_id);
But what you really should do is adding a foreign key constraint so that such rows cannot exist in the first place. Assuming that "user".id already is a (primary) key:
ALTER TABLE notification
ADD FOREIGN KEY (user_id)
REFERENCES "user"
(id);
If "user".id isn't a (primary) key, you first need to change that and make it a (primary) key.
Let's say I have 2 tables: Students and Groups.
The Group table has 2 columns: id, GroupName
The Student table has 3 columns: id, StudentName and GroupID
The GroupID is a foreign key to a Group field.
I need to import the Students table from a CSV, but in my CSV instead of the Group id appears the name of the group. How can I import it with pgAdmin without modifying the csv?
Based on Laurenz answer, use follwoing scripts:
Create a temp table to insert from CSV file:
CREATE TEMP TABLE std_temp (id int, student_name char(25), group_name char(25));
Then, import the CSV file:
COPY std_temp FROM '/home/username/Documents/std.csv' CSV HEADER;
Now, create std and grp tables for students and groups:
CREATE TABLE grp (id int, name char(25));
CREATE TABLE std (id int, name char(20), grp_id int);
It's grp table's turn to be populated based on distinct value of group name. Consider how row_number() is use to provide value for id`:
INSERT INTO grp (id, name) select row_number() OVER (), * from (select distinct group_name from std_temp) as foo;
And the final step, select data based on the join then insert it into the std table:
insert into std (id, name, grp_id) select std_temp.id, std_temp.student_name,grp.id from std_temp inner join grp on std_temp.group_name = grp.name;
At the end, retreive data from final std table:
select * from std;
Your easiest option is to import the file into a temporary table that is defined like the CSV file. Then you can join that table with the "groups" table and use INSERT INTO ... SELECT ... to populate the "students" table.
There is of course also the option to define a view on a join of the two tables and define an INSTEAD OF INSERT trigger on the view that inserts values into the underlying tables as appropriate. Then you could load the data directly to the view.
The suggestion by #LaurenzAlbe is the obvious approach (IMHO never load a spreadsheet directly to
your tables, they are untrustworthy beasts). But I believe your implementation after loading the staging
table is flawed.
First, using row_number() virtually ensures you get duplicated ids for the same group name.
The ids will always increment from 1 by 1 to then number of group names no matter the number of groups previously loaded and you cannot ensure the identical sequence on a subsequent spreadsheets. What happens when you have a group that does not previously exist.
Further there is no validation that the group name does not already exist. Result: Duplicate group names and/or multiple ids for the same name.
Second, you attempt to use the id from the spreadsheet as the id the student (std) table is full of error possibilities. How do you ensure that number is unique across spreadsheets?
Even if unique in a single spreadsheet, how do you ensure another spreadsheet does not use the same numbers as a previous one. Or assuming multiple users create the spreadsheets that one users numbers do not overlap another users even if all users
user are very conscious of the numbers they use. Result: Duplicate id numbers.
A much better approach would be to put a unique key on the group table name column then insert any group names from the stage table into the group trapping any duplicate name errors (using on conflict). Then load the student table directly from the stage table
while selecting group id from the group table by the (now unique) group name.
create table csv_load_temp( junk_num integer, student_name text, group_name text);
create table groups( grp_id integer generated always as identity
, name text
, grp_key text generated always as ( lower(name) ) stored
, constraint grp_pk
primary key (grp_id)
, constraint grp_bk
unique (grp_key)
);
create table students (std_id integer generated always as identity
, name text
, grp_id integer
, constraint std_pk
primary key (std_id)
, constraint std2grp_fk
foreign key (grp_id)
references groups(grp_id)
);
-- Function to load Groups and Students
create or replace function establish_students()
returns void
language sql
as $$
insert into groups (name)
select distinct group_name
from csv_load_temp
on conflict (grp_key) do nothing;
insert into students (name, grp_id)
select student_name, grp_id
from csv_load_temp t
join groups grp
on (grp.name = t.group_name);
$$;
The groups table requires Postgres v12. For prior versions remove the column grp_key couumn
and and put the unique constraint directly on the name column. What to do about capitalization is up to your business logic.
See fiddle for full example. Obviously the 2 inserts in the Establish_Students function can be run standalone and independently. In that case the function itself is not necessary.
I have a query which works fine on SQLite, but when I run it on the same data in Postgresql I get:
column "role.id" must appear in the GROUP BY clause or be used in an aggregate function
I have three tables, for people, exhibitions, and a table that links the two: "One person in one exhibition performing a particular role" (such as "Artist" or "Curator"):
CREATE TABLE "person" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
"name" varchar(255));
CREATE TABLE "exhibition" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
"name" varchar(255));
CREATE TABLE "role" (`id` integer NOT NULL PRIMARY KEY AUTOINCREMENT,
`name` varchar(30) NOT NULL,
`exhibition_id` integer NOT NULL,
`person_id` integer NOT NULL,
FOREIGN KEY(`exhibition_id`) REFERENCES `exhibition`(`id`),
FOREIGN KEY(`person_id`) REFERENCES `person`(`id`));
I want to display the people involved in an exhibition ordered by how many things they've done. So, I get the IDs of the people in an exhibition (1,2,3,4) and then do this:
SELECT
*,
COUNT(person.id) AS role_count
FROM person
INNER JOIN role
ON person.id = role.person_id
WHERE person.id IN ( 1, 2, 3, 4 )
GROUP BY person.id
ORDER BY role_count DESC
That orders the people by role_count, which is the number of roles they've had across all exhibitions
It works fine on SQLite, but not in Postgresql. I've tried putting role.id into the GROUP BY (instead of, and as well as, person.id) but that changes the results.
You know when you struggle for ages, post an SO question, and then immediately stumble on the answer?
From this answer I realised that I couldn't select role.id (which the SELECT * is implicitly doing) as it wasn't in the GROUP BY.
I couldn't add it to the GROUP BY (because that changes the results) so the solution was to not select it.
So I changed the SELECT part to:
SELECT
person.*,
COUNT(person.id) AS role_count
FROM person
...
Now role.id is not being selected. And that works.
If I needed any other fields from the role table, like name, I could add those explicitly too:
SELECT
person.*,
role.name,
COUNT(person.id) AS role_count
FROM person
...
Just like the error says, Standard SQL doesn't let you SELECT anything other than one of the GROUP BY columns or a call to an aggregate function. (For a logical reason: How would the RDBMS know which role.id to select when there are multiple rows to select from within a group?) PostgreSQL actually enforces this rule; SQLite ignores it and just returns data from an arbitrary row in the group.
As you discovered, omitting role.id from the SELECT fixes your error. But if you do want SQLite's behavior of selecting the ID from an arbitrary row, you can simply wrap it in an aggregate function, e.g., SELECT MAX(role.id) instead of just SELECT role.id).
I have two tables one is role and another one is user_role. User_role table contains all users of particular role. Now, i added two extra new roles into the role table. I want to insert the rows into user_role table who has role_id=4 with the new role_ids. I cannot update exsting rows because i want exsting rows also means the users who have role_id=4 also belongs to new role_ids.
I tried in this way
INSERT INTO table2 (all_links, fields_one, fields_two)
select URI, fields, details FROM table1
WHERE date > "12-11-2013 00-00-00";
But here two tables are there, but in my case only one table is there. And in user_role table id is sequene so cant select from another table dirctely and do insert.
Please help on these.
You can select and insert records into the same table.
If I understood your use case correctly,
INSERT INTO user_role (role_id, <other columns>)
SELECT <new_role_id>, <other columns>
FROM
user_role
WHERE
role_id = 4.
This will insert all the existing records in user_role table with role_id as 4, into the same table with a different role_id. HTH.
I need to duplicate selected rows with all the fields exactly same except ID ident int which is added automatically by SQL.
What is the best way to duplicate/clone record or records (up to 50)?
Is there any T-SQL functionality in MS SQL 2008 or do I need to select insert in stored procedures ?
The only way to accomplish what you want is by using Insert statements which enumerate every column except the identity column.
You can of course select multiple rows to be duplicated by using a Select statement in your Insert statements. However, I would assume that this will violate your business key (your other unique constraint on the table other than the surrogate key which you have right?) and require some other column to be altered as well.
Insert MyTable( ...
Select ...
From MyTable
Where ....
If it is a pure copy (minus the ID field) then the following will work (replace 'NameOfExistingTable' with the table you want to duplicate the rows from and optionally use the Where clause to limit the data that you wish to duplicate):
SELECT *
INTO #TempImportRowsTable
FROM (
SELECT *
FROM [NameOfExistingTable]
-- WHERE ID = 1
) AS createTable
-- If needed make other alterations to the temp table here
ALTER TABLE #TempImportRowsTable DROP COLUMN Id
INSERT INTO [NameOfExistingTable]
SELECT * FROM #TempImportRowsTable
DROP TABLE #TempImportRowsTable
If you're able to check the duplication condition as rows are inserted, you could put an INSERT trigger on the table. This would allow you to check the columns as they are inserted instead of having to select over the entire table.