Given a table defined as such:
CREATE TABLE test_values(name TEXT, values INTEGER[]);
...and the following values:
| name | values |
+-------+---------+
| hello | {1,2,3} |
| world | {4,5,6} |
I'm trying to find a query which will return:
| name | value |
+-------+-------+
| hello | 1 |
| hello | 2 |
| hello | 3 |
| world | 4 |
| world | 5 |
| world | 6 |
I've reviewed the upstream documentation on accessing arrays, and tried to think about what a solution using the unnest()
function would look like, but have been coming up empty.
An ideal solution would be easy to use even in cases where there were a significant number of columns other than the array being expanded and no primary key. Handling a case with more than one array is not important.
We can put the set-returning function unnest()
into the SELECT
list like Raphaël suggests. This used to exhibit corner case problems before Postgres 10. See:
Since Postgres 9.3 we can also use a LATERAL
join for this. It is the cleaner, standard-compliant way to put set-returning functions into the FROM
list, not into the SELECT
list:
SELECT name, value
FROM tbl, unnest(values) value; -- implicit CROSS JOIN LATERAL
One subtle difference: this drops rows with empty / NULL values
from the result since unnest()
returns no row, while the same is converted to a NULL value in the FROM
list and returned anyway. The 100 % equivalent query is:
SELECT t.name, v.value
FROM tbl t
LEFT JOIN unnest(t.values) v(value) ON true;
See: