I would like to insert new row in profit table for each user that exist in db: select id * from users. The number of users is dynamic, so I need to fetch them all. I need some loop in postgres sql. I have problem to figure it out on my own. It would be something like that:
select id * from users as user_ids
for (each userId in user_ids) {
insert into profit (user_id, value) values (userId, 23);
}
Can I ask You for help? I've went for many questions already:
Insert new row with data computed from other rows
postgresSQL insert multiple rows, of id returned from select queries
No luck so far
Thinking in "loops" is almost always wrong when working with SQL. You need to think in terms of sets and how you operate on them. SQL statement describe exactly that: how to retrieve a set and what to do with that set of rows.
In this case, you can use a SELECT statement as the source for an INSERT:
insert into profit (user_id, value)
select id, 23
from users;
Note that you don't have a values clause in this case.
Related
For a table like this one:
CREATE TABLE Users(
id SERIAL PRIMARY KEY,
name TEXT UNIQUE
);
What would be the correct one-query insert for the following operation:
Given a user name, insert a new record and return the new id. But if the name already exists, just return the id.
I am aware of the new syntax within PostgreSQL 9.5 for ON CONFLICT(column) DO UPDATE/NOTHING, but I can't figure out how, if at all, it can help, given that I need the id to be returned.
It seems that RETURNING id and ON CONFLICT do not belong together.
The UPSERT implementation is hugely complex to be safe against concurrent write access. Take a look at this Postgres Wiki that served as log during initial development. The Postgres hackers decided not to include "excluded" rows in the RETURNING clause for the first release in Postgres 9.5. They might build something in for the next release.
This is the crucial statement in the manual to explain your situation:
The syntax of the RETURNING list is identical to that of the output
list of SELECT. Only rows that were successfully inserted or updated
will be returned. For example, if a row was locked but not updated
because an ON CONFLICT DO UPDATE ... WHERE clause condition was not
satisfied, the row will not be returned.
Bold emphasis mine.
For a single row to insert:
Without concurrent write load on the same table
WITH ins AS (
INSERT INTO users(name)
VALUES ('new_usr_name') -- input value
ON CONFLICT(name) DO NOTHING
RETURNING users.id
)
SELECT id FROM ins
UNION ALL
SELECT id FROM users -- 2nd SELECT never executed if INSERT successful
WHERE name = 'new_usr_name' -- input value a 2nd time
LIMIT 1;
With possible concurrent write load on the table
Consider this instead (for single row INSERT):
Is SELECT or INSERT in a function prone to race conditions?
To insert a set of rows:
How to use RETURNING with ON CONFLICT in PostgreSQL?
How to include excluded rows in RETURNING from INSERT ... ON CONFLICT
All three with very detailed explanation.
For a single row insert and no update:
with i as (
insert into users (name)
select 'the name'
where not exists (
select 1
from users
where name = 'the name'
)
returning id
)
select id
from users
where name = 'the name'
union all
select id from i
The manual about the primary and the with subqueries parts:
The primary query and the WITH queries are all (notionally) executed at the same time
Although that sounds to me "same snapshot" I'm not sure since I don't know what notionally means in that context.
But there is also:
The sub-statements in WITH are executed concurrently with each other and with the main query. Therefore, when using data-modifying statements in WITH, the order in which the specified updates actually happen is unpredictable. All the statements are executed with the same snapshot
If I understand correctly that same snapshot bit prevents a race condition. But again I'm not sure if by all the statements it refers only to the statements in the with subqueries excluding the main query. To avoid any doubt move the select in the previous query to a with subquery:
with s as (
select id
from users
where name = 'the name'
), i as (
insert into users (name)
select 'the name'
where not exists (select 1 from s)
returning id
)
select id from s
union all
select id from i
I'm trying to avoid writing separate SQL queries to achieve the following scenario:
I have a Table called Values:
Values:
id INT (PK)
data TEXT
I would like to check if certain data exists in the table, and if it does, return its id, otherwise insert it and return its id.
The (very) naive way would be:
select id from Values where data = "SOME_DATA";
if id is not null, take it.
if id is null then:
insert into Values(data) values("SOME_DATA");
and then select it again to see its id or use the returned id.
I am trying to make the above functionality in one line.
I think I'm getting close, but I couldn't make it yet:
So far I got this:
select id from Values where data=(COALESCE((select data from Values where data="SOME_DATA"), (insert into Values(data) values("SOME_DATA"));
I'm trying to take advantage of the fact that the second select will return null and then the second argument to COALESCE will be returned. No success so far. What am I missing?
Your command does not work because in SQL, INSERT does not return a value.
If you have a unique constraint/index on the data column, you can use that to prevent duplicates if you blindly insert the value; this uses SQLite's INSERT OR IGNORE extension:
INSERT OR IGNORE INTO "Values"(data) VALUES('SOME_DATE');
SELECT id FROM "Values" WHERE data = 'SOME_DATA';
I'm very new at SQL scripts and couldn't figure out how to make a specific for each loop. I need to do something like this:
I have Sites and SiteCrawls tables.
Basically, for every site I need to create a new SiteCrawl and that SiteCrawl's Site_ID column will equal to that site's ID.
How can I do this?
insert SiteCrawl
(
Site_ID
)
select
s.Site_ID
from Site as s
where s.Site_ID not in (select Site_ID from SiteCrawl)
insert into site_crawl (site_id) values (select site_id from site);
So basically: there is no specific for/each in plain SQL, you handle tables and rows of results always as one statement.
So you could also say: there is no way an SQL Statement is something else than a for/each.
With that knowledge, you can see that the above query will insert one row into site_crawl for every site_id in the site table. You most likely want to use more values than this, but given the information from your question that is all I can do for you :)
Also: you want to read more about what sql is and how its used.
Have fun, SQL is a lot of fun!
In SQL you typically don't want to loop over every record. It's very inefficient.
You could do something like
insert into SiteCrawl (Site_Id)
select Id from Sites
insert into SiteCrawls (SiteID)
select SiteID
from Sites
you can do it by trigger
CREATE TRIGGER tg AFTER INSERT ON `Sites`
FOR EACH ROW
BEGIN
insert into SiteCrawls(Site_ID) values (NEW.id);
END
;
I have a table connecting principals to their roles. I have come upon a situation where I need to add a role for each user. I have a statement SELECT id FROM principals which grabs a list of all the principals. What I want to create is something like the following:
INSERT INTO role_principal(principal_id,role_id)
VALUES(SELECT id FROM principals, '1');
so for each principal, it creates a new record with a role_id=1. I have very little SQL experience, so I dont know if I can do this as simply as I would like to or if there is some sort of loop feature in SQL that I could use.
Also, this is for a mySQL db (if that matters)
Use VALUES keyword if you want to insert values directly. Omit it to use any SELECT (where column count and type matches) to get the values from.
INSERT INTO role_principal(principal_id,role_id)
(SELECT id, 1 FROM principals);
To avoid duplicates is useful to add a subquery :
INSERT INTO role_principal(principal_id,role_id)
(SELECT id, 1 FROM principals p
WHERE NOT EXISTS
(SELECT * FROM role_principal rp WHERE rp.principal_id=p.id AND role_id=1)
)
Is there a way i can do multiple inserts into one table using a condition?
i have a list of subscribers in tbl_subscribers. i have an update on productX so i would like everyone who is subscribes to productX to get a notification. The user_notification table is id PK, user_id, notification_id. The two values i need is product_id (productX) which allows me to find a list of subscribers in tbl_subscribers and the notification_id to insert into the user_notification table.
How can i do this insert using one query? I see you can do a select statement in sqlite http://www.sqlite.org/lang_insert.html but i cannot wrap my head around how i may do this nor seen an example.
I believe you're looking from INSERT SELECT as outlined here:
http://www.1keydata.com/sql/sqlinsert.html
The second type of INSERT INTO allows
us to insert multiple rows into a
table. Unlike the previous example,
where we insert a single row by
specifying its values for all columns,
we now use a SELECT statement to
specify the data that we want to
insert into the table. If you are
thinking whether this means that you
are using information from another
table, you are correct. The syntax is
as follows:
INSERT INTO "table1" ("column1", "column2", ...)
SELECT "column3", "column4", ... FROM "table2"
insert into user_notification(user_id, notification_id)
select s.user_id, #notification_id
from tbl_subscriber s
where s.product_id = #productX