Split Column into Multiple Rows in Postgres

Split column into multiple rows in Postgres

In Postgres 9.3+ use a LATERAL join. Minimal form:

SELECT token, flag
FROM   tbl, unnest(string_to_array(subject, ' ')) token
WHERE  flag = 2;

The comma in the FROM list is (almost) equivalent to CROSS JOIN, LATERAL is automatically assumed for set-returning functions (SRF) in the FROM list. Why "almost"? See:

• "invalid reference to FROM-clause entry for table" in Postgres query

The alias "token" for the derived table is also assumed as column alias for a single anonymous column, and we assumed distinct column names across the query. Equivalent, more verbose and less error-prone:

SELECT s.token, t.flag
FROM   tbl t
CROSS  JOIN LATERAL unnest(string_to_array(subject, ' ')) AS s(token)
WHERE  t.flag = 2;

Or move the SRF to the SELECT list, which is allowed in Postgres (but not in standard SQL), to the same effect:

SELECT unnest(string_to_array(subject, ' ')) AS token, flag
FROM   tbl
WHERE  flag = 2;

The last one seems acceptable since SRF in the SELECT list have been sanitized in Postgres 10. See:

• What is the expected behaviour for multiple set-returning functions in SELECT clause?

If unnest() does not return any rows (empty or NULL subject), the (implicit) join eliminates the row from the result. Use LEFT JOIN ... ON true to keep qualifying rows from tbl. See:

• What is the difference between LATERAL JOIN and a subquery in PostgreSQL?

We could also use regexp_split_to_table(), but that's typically slower because regular expressions cost a bit more. See:

• SQL select rows containing substring in text field
• PostgreSQL unnest() with element number

Postgres, split single row into multiple rows

In Postgres, you can efficiently unpivot the columns to rows with a lateral join:

select x.*
from mytable as t
cross join lateral (values 
    (t.age1, t.val1), 
    (t.age2, t.val2), 
    (t.age3, t.val3)
) as x(age, val)

Postgres: Split column values & transpose

You can use PostgreSQL's array manipulation functions:

SELECT category_id, unnest(string_to_array(product_id, ';')) FROM test;

string_to_array does exactly what it says — splits a string into an array of parts using a supplied delimiter, then unnest is used to separate an array value into multiple rows containing elements from the array.

Split value in single row to multiple rows with Postgresql

You could create an array and then use UNNEST():

SELECT UNNEST(ARRAY[1,2,3]);

Postgresql split column into rows

Try this:

SELECT 
    username, 
    regexp_split_to_table(towns, E',') 
FROM yourTable

SQLFIDDLE DEMO

Postgres - Splitting a row into multiple rows based on two datetime fields to get logged minutes each hour

We can approach this by first generating a calendar table covering all minutes on all dates in your data set. Then, inner join to your data table and aggregate by the hour (and day) to generate the counts:

WITH dates AS (
    SELECT '2021-04-05'::date AS dt UNION ALL
    SELECT '2021-04-06'::date
),
minutes AS (
    SELECT (n || ' minute')::INTERVAL AS min
    FROM generate_series(0, 1439) n
)

SELECT
    DATE_TRUNC('hour', d.dt + m.min),
    COUNT(*) AS minutes_logged
FROM dates d
CROSS JOIN minutes m
INNER JOIN yourTable t
   ON d.dt + m.min >= t.started_at AND d.dt + m.min < t.end_at
GROUP BY DATE_TRUNC('hour', d.dt + m.min)
ORDER BY DATE_TRUNC('hour', d.dt + m.min);

Demo

---

Note: To support wide range of start and end dates following can be implemented

    with dates AS (
        select * from generate_series(timestamp '2019-12-08'::date, '2021-04-09'::date, '1 day') as dt
    ),

Split column and values into multiple rows in Postgres

You can use generate_series() to produce list of consecutive days between first_date and last_date:

with dates as (
    select d::date, last_date- first_date+ 1 ct
    from test, generate_series(first_date, last_date, '1d'::interval) d
    )
select subject, flag/ ct flag, d date
from dates
cross join test;

    subject     |          flag          |    date    
----------------+------------------------+------------
 this is a test | 0.50000000000000000000 | 2016-01-01
 this is a test | 0.50000000000000000000 | 2016-01-02
 this is a test | 0.50000000000000000000 | 2016-01-03
 this is a test | 0.50000000000000000000 | 2016-01-04
(4 rows)    

---

Related Topics