[GitHub] maropu commented on issue #20433: [SPARK-23264][SQL] Make INTERVAL keyword optional in INTERVAL clauses

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maropu commented on issue #20433: [SPARK-23264][SQL] Make INTERVAL keyword optional in INTERVAL clauses
URL: https://github.com/apache/spark/pull/20433#issuecomment-464451209
 
 
   I checked if the time unit keywords (YEAR, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND, WEEK, MILLISECOND, MICROSECOND) are reserved in SQL-2011/database implementations:
   
   SQL-2011
    - reserved: YEAR, MONTH, DAY, HOUR, MINUTE, SECOND
    - non-reserved: WEEK, MILLISECOND, MICROSECOND
   
   PostgreSQL, MySQL, Oracle, and SQL Server
    - reserved:
    - non-reserved: YEAR, MONTH, WEEK, DAY, HOUR, MINUTE, SECOND, MILLISECOND, MICROSECOND
   
   Also, all the the plural forms (YEARS, MONTHS, ...) are not reserved in all the cases.
   I'm not sure about the historical reason why these databases don't handle them as reserved though, IMHO we would be better to follow SQL-2011; YEAR, MONTH, DAY, HOUR, MINUTE, and SECOND are reserved if ansi=true.
   
   As for SQL server, these time unit keywords are listed in future keywords:
   https://docs.microsoft.com/ja-jp/sql/t-sql/language-elements/reserved-keywords-transact-sql?view=sql-server-2017#future-keywords

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