"January",31,
"February",28,
"March",31,
"April",30,
"May",31,
"June",30,
"July",31,
"August",31,
"September",30,
"October",31,
"November",30,
"December",31,
30)
CASE(MID(Custom__c, 4, 3),
"Jan", 1, "Feb", 2, "Mar", 3, "Apr", 4, "May", 5, "Jun", 6,
"Jul", 7, "Aug", 8, "Sep", 9, "Oct", 10, "Nov", 11, "Dec", 12, 0)
日曜日 Sunday = Sun. = Su.
月曜日 Monday= Mon.= Mo.
火曜日 Tuesday= Tue.(Tues.) = Tu.
水曜日 Wednesday= Wed.= We.
木曜日 Thursday= Thu.= Th.
金曜日 Friday= Fri.= Fr.
土曜日 Saturday= Sat.= Sa.
CASE(
IF(DAY(Amendment_Date__c) = 1,MONTH(ADDMONTHS(Amendment_Date__c,-1)),MONTH(Amendment_Date__c)),
1,"January",
2,"February",
3,"March",
4,"April",
5,"May",
6,"June",
7,"July",
8,"August",
9,"September",
10,"October",
11,"November",
"December")