多行变成单行

teledb=# select array_to_string(array(select nickname from teledb_pg1),',');
 array_to_string 
-----------------
 test,pg
(1 row)

一列变成多行

teledb=# insert into teledb_pg1 values(6, 'teledb, teledb1');
INSERT 0 1

teledb=# select regexp_split_to_table((select nickname from teledb_pg1 where id=6 limit 1), ',');
 regexp_split_to_table 
-----------------------
 teledb
  teledb1
(2 rows)