在 Ruby Sequel 库的 "having" 块中使用相等比较

Question

我正在尝试通过 Sequel 在 Ruby（Ruby 2.5.7，Sequel 5.28. 0), 但在使用相等比较时遇到问题。

所有文档和示例都表明构建 having 块适用于 <、>、<= 和 >= 等运算符。但是，= 抛出 SyntaxError.

如果我使用 > 构建 having 语句，我会正确地得到 SQL：

query.having do sum(Sequel.case({{column => nil} => 1}, 0)) > count.function.* end
=> #<Sequel::Postgres::Dataset: "SELECT * FROM \"schema\".\"table\" GROUP BY \"id\" HAVING (sum((CASE WHEN (\"column\" IS NULL) THEN 1 ELSE 0 END)) > count(*))">

但是如果我将 > 更改为 =，我会得到一个 SyntaxError:

query.having do sum(Sequel.case({{column => nil} => 1}, 0)) = count.function.* end
SyntaxError: unexpected '=', expecting keyword_end
...nil} => 1}, 0)) = count.function.* end
...                              ^
SyntaxError: unexpected keyword_end, expecting end-of-input
... 1}, 0)) = count.function.* end
...                            ^~~

在这种情况下，什么是有效的 = 运算符？我在显示此用法的 Sequel 文档或规范中找不到提及。如果我错过了这个，抱歉，如果有人指出我该信息所在的位置，我很乐意重新阅读。

== 和 <=> 都会导致不希望的和不准确的 SQL，而且我也无法通过 <= 和 [=19= 的组合来破解它] 因为 having 块似乎没有将 && 识别为多个条件（它只接受最后一个条件）。

query.having do sum(Sequel.case({{column => nil} => 1}, 0)) == count.function.* end
=> #<Sequel::Postgres::Dataset: "SELECT * FROM \"schema\".\"table\" GROUP BY \"id\" HAVING false">

query.having do sum(Sequel.case({{column => nil} => 1}, 0)) <=> count.function.* end
=> #<Sequel::Postgres::Dataset: "SELECT * FROM \"schema\".\"table\" GROUP BY \"id\" HAVING false">

query.having do sum(Sequel.case({{column => nil} => 1}, 0)) >= count.function.* && sum(Sequel.case({{column => nil} => 1}, 0)) <= count.function.* end
=> #<Sequel::Postgres::Dataset: "SELECT * FROM \"schema\".\"table\" GROUP BY \"id\" HAVING (sum((CASE WHEN (\"column\" IS NULL) THEN 1 ELSE 0 END)) <= count(*))">

Answer 1

根据这个 this discussion，这应该可以工作，将它包装在一个虚拟行中并使用 =>

的散列

query.having do 
  { sum(Sequel.case({{column => nil} => 1}, 0)) => count.function.* }
end

或使用=~

query.having do 
  sum(Sequel.case({{column => nil} =~ 1}, 0)) == count.function.* 
end

在 Ruby Sequel 库的 "having" 块中使用相等比较

Using equality comparison in Ruby Sequel library's "having" block

ruby

sequel