postgresql中可能的值数组？

Question

我有以下数据：

letter  number
A       1
A       2
B       3
B       4
C       5
C       6

如何在Postgres中编写一个select语句，将这些数据选择到一个包含每个字母所有可能数字数组的表中？

letter  number array
A       {1,2}
B       {3,4}
C       {5,6}

Answer 1

select letter, array_agg(number) as numbers
from the_table
group by letter;

另见手册：http://www.postgresql.org/docs/current/static/functions-aggregate.html

Answer 2

如果您的Postgres版本没有“array_agg”功能，您可以尝试这样：

select letter, 
       array( 
              select number 
                from the_table t2 
               where t2.letter = t1.letter
            order by number                   
            ) as numbers
from the_table t1
group by letter;