无法替换RSQLite查询中的空值

Question

我查询数据库以创建用于绘图的数据框，我的一个数据转换需要数学运算，因此我需要将特定列的空条目改为零。但是，我无法获取要替换的空值。

这是一个示例输出与预期输出：

Actual:
  income travel_spending sports_leisure_spending gender percent_travel
1     25              33                      NA      M     1.32000000
2    357             136                      NA      M     0.38095238
3     25              18                       5      M     0.72000000
4     51             527                      NA      M    10.33333333
5     51             527                      NA      F    10.33333333
6     48               4                      60      F     0.08333333

Expected:
  income travel_spending sports_leisure_spending gender percent_travel
1     25              33                       0      M     1.32000000
2    357             136                       0      M     0.38095238
3     25              18                       5      M     0.72000000
4     51             527                       0      M    10.33333333
5     51             527                       0      F    10.33333333
6     48               4                      60      F     0.08333333

这是我的代码。有问题的专栏是sports_leisure_spending：

query <- 'SELECT income, REPLACE(travel_spending, "33", "33") AS travel_spending, 
    CASE sports_leisure_spending WHEN "NA" THEN "0" ELSE sports_leisure_spending END AS sports_leisure_spending, 
    gender, CAST(travel_spending AS float)/CAST(income AS float) AS percent_travel FROM customer'

我还尝试了以下方法：

REPLACE(sports_leisure_spending, "NA", "0") -> does nothing
REPLACE(sports_leisure_spending, NA, "0") -> does nothing
REPLACE(sports_leisure_spending, NULL, "0") -> makes EVERYTHING NA
REPLACE(sports_leisure_spending, "", "0") -> does nothing