Java String split function

Java的String物件中，有個split function，
平常使用String.split("分隔字串")均可以將字串做分隔，
但，當原字串中，尾端若有連續出現的"分隔字串"時，
卻會被忽略。
例：
"a,b,c,d".split(",") = [a, b, c, d]
"a,b,c,d,,,".split(",") = [a, b, c, d]
但若改為
"a,b,c,d,,,".split(",", -1) = [a, b, c, d, "", "", ""]

原因為
"a,b,c,d,,,".split(",") = "a,b,c,d,,,".split(",", 0)
於是，尾端的空白值都會被忽略。

Java API Doc裡有提到：
This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.

List Informix instances

onstat -g dis

ref from here

Oracle listagg distinct

select col1, 
regexp_replace(
    listagg(col2, ',') within group (order by col2)
    ,'([^,]+)(,\1)+', '\1')
where rn = 1
group by col1;

ref from here

Oracle connection數上限 - 查詢

--The number of sessions the database was configured to allow

SELECT name, value 
  FROM v$parameter
 WHERE name = 'sessions';

--The number of sessions currently active

SELECT COUNT(*)
  FROM v$session;