「PostgreSQL 14.4]to_char関数にrmを指定して月をローマ小文字数字で取得する方法

2022年7月31日

環境
OSバージョンの確認

# cat /etc/redhat-release
Rocky Linux release 9.0 (Blue Onyx)

PostgreSQLバージョンの確認

# psql --version
psql (PostgreSQL) 14.4

構文
to_char(date '指定日付’, 'rm’)
to_char関数にパターン「rm」を指定して、月をローマ数字で取得します。
パタンー rm
ローマ数字による月 (i-xii： i=1月) (小文字)

使用例

SELECT 
  to_char(date '2022-01-01', 'rm') AS "January",
  to_char(date '2022-02-01', 'rm') AS "February",
  to_char(date '2022-03-01', 'rm') AS "March",
  to_char(date '2022-04-01', 'rm') AS "April",
  to_char(date '2022-05-01', 'rm') AS "May",
  to_char(date '2022-06-01', 'rm') AS "June",
  to_char(date '2022-07-01', 'rm') AS "July",
  to_char(date '2022-08-01', 'rm') AS "August",
  to_char(date '2022-09-01', 'rm') AS "September",
  to_char(date '2022-10-01', 'rm') AS "October",
  to_char(date '2022-11-01', 'rm') AS "November",
  to_char(date '2022-12-01', 'rm') AS "December";

実行結果

January	February	March	April	May	June	July	August	September	October	November	December
i   	ii  	        iii 	iv  	v   	 vi  	vii 	viii	ix  	        x   	xi  	         xii