How to Show Row Numbers in Postgresql Query

How to show row numbers in PostgreSQL query?


select   row_number() over (order by <field> nulls last) as rownum, *
from foo_tbl
order by <field>

If order is not necessary, this answer may also be simplified:

select row_number() over(), *  -- notice: no fields are needed
from foo_tbl

SQL Fiddle Proof of Concept

Postgres: How to get row number when ordered by the result of operation?

Try:

WITH summary AS (
SELECT
i.id,
i.pos - i.neg AS diff,
ROW_NUMBER() OVER(ORDER BY (i.pos - i.neg)) AS position
FROM items i)
SELECT s.* FROM summary s WHERE s.id = 351435254

How do you find the row count for all your tables in Postgres

There's three ways to get this sort of count, each with their own tradeoffs.

If you want a true count, you have to execute the SELECT statement like the one you used against each table. This is because PostgreSQL keeps row visibility information in the row itself, not anywhere else, so any accurate count can only be relative to some transaction. You're getting a count of what that transaction sees at the point in time when it executes. You could automate this to run against every table in the database, but you probably don't need that level of accuracy or want to wait that long.

WITH tbl AS
(SELECT table_schema,
TABLE_NAME
FROM information_schema.tables
WHERE TABLE_NAME not like 'pg_%'
AND table_schema in ('public'))
SELECT table_schema,
TABLE_NAME,
(xpath('/row/c/text()', query_to_xml(format('select count(*) as c from %I.%I', table_schema, TABLE_NAME), FALSE, TRUE, '')))[1]::text::int AS rows_n
FROM tbl
ORDER BY rows_n DESC;

The second approach notes that the statistics collector tracks roughly how many rows are "live" (not deleted or obsoleted by later updates) at any time. This value can be off by a bit under heavy activity, but is generally a good estimate:

SELECT schemaname,relname,n_live_tup 
FROM pg_stat_user_tables
ORDER BY n_live_tup DESC;

That can also show you how many rows are dead, which is itself an interesting number to monitor.

The third way is to note that the system ANALYZE command, which is executed by the autovacuum process regularly as of PostgreSQL 8.3 to update table statistics, also computes a row estimate. You can grab that one like this:

SELECT 
nspname AS schemaname,relname,reltuples
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE
nspname NOT IN ('pg_catalog', 'information_schema') AND
relkind='r'
ORDER BY reltuples DESC;

Which of these queries is better to use is hard to say. Normally I make that decision based on whether there's more useful information I also want to use inside of pg_class or inside of pg_stat_user_tables. For basic counting purposes just to see how big things are in general, either should be accurate enough.

Row_number() in postgresql

Postgres does allow the syntax:

select row_number() over (), . . .

However, that does not necessary return the row numbers in the ordering specified by the outer order by. I think Postgres calculates the row number before the order by.

You might be tempted to use:

select row_number() over (), . . .
from (select . . .
from . . .
order by . . .
) t;

And, this would seem to do what you want (one a single processor machine, for instance, it just did the right thing). However, this is not guaranteed to work. The ordering in a subquery does not apply to the outer query (although this might only be visible on multi-processor machines).

My advice? Simply repeat the order by twice (using either the expression or the alias). That is guaranteed to work. And, you might be surprised at the optimizer only needing to sort the data once.

Rownum in postgresql

Postgresql > 8.4

SELECT 
row_number() OVER (ORDER BY col1) AS i,
e.col1,
e.col2,
...
FROM ...

Get row number of a row that meets an x condition in Postgresql

I guess I rushed a little. Sorry.
I already found the solution. The following query worked for me:

SELECT num FROM (SELECT Row_Number() OVER () AS num, country FROM people ORDER BY country) AS tabla WHERE country='France'

Incrementing row numbers by condition in postgres

demo:db<>fiddle

You can use the cumulative SUM() function with a conditional value: Add 1 if the condition is met, 0 otherwise:

SELECT
*,
SUM(
CASE
WHEN diff >= 5 THEN 1
ELSE 0
END
) OVER (ORDER BY ts)
FROM --<your query>


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