Proc-SQL：嵌套时的情况

使用procsql中的嵌套case，我需要根据指定的年份和月份获取列的值。例如，如果年份为2018，月份为12月，则应返回x201811列的值，如果为空，则应返回零。我在下面编写的代码给出了一个语法错误。请提出解决办法

CASE  WHEN (( Year(date) = 2018 ) AND ( Month(date) = 12 )) THEN x201811 
     WHEN x201811 IS NULL THEN 0
   ELSE x201811
   WHEN ((Year(date)=2018) AND (Month(Date)=11)) THEN x201810
    WHEN x201810 IS NULL THEN 0
   ELSE x201810

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您可以使用

COALESCE

函数使第一个非空值成为指定值

CASE
  WHEN (( Year(date) = 2018 ) AND ( Month(date) = 12 )) 
  THEN coalesce (x201811, 0)

  WHEN ((Year(date)=2018) AND (Month(Date)=11)) 
  THEN coalesce (x201810, 0)

  ELSE coalesce (x201810, 0)
END as got_a_value

另一种方法是嵌套

CASE

语句

CASE
  WHEN (( Year(date) = 2018 ) AND ( Month(date) = 12 )) 
  THEN CASE WHEN x201811 is null then 0 else x201811 end

  WHEN ((Year(date)=2018) AND (Month(Date)=11))
  THEN CASE WHEN x201810 is null then 0 else x201810 end

  ELSE ...
END as got_a_value