如何避免FOR JSON PATH逃离查询结果？

Question

我试图编写一个相当复杂的SQL查询来生成JSON。除了一些硬编码数组，我需要在层次结构中有更深层次的东西，我必须使用UNION ALL来创建。我已经产生了查询，这里显示了我的问题（没有数据是必需的 - 我在Azure的SQL数据库上运行此）：

SELECT 
    'Hi' AS Greeting, 
    (
     SELECT 
      CASE WHEN DatePart(second, GetDate()) % 2 = 1 THEN 
       'qwerty' 
      ELSE 
       'asdf' 
      END AS Stuff 
     FOR JSON PATH 
    ) AS StuffArray, 
    (
     CASE WHEN DatePart(second, GetDate()) % 2 = 1 THEN 
     (
      SELECT 'qwerty' AS Stuff 
      FOR JSON PATH 
     ) 
     ELSE 
     (
      SELECT 'asdf' AS Stuff 
      FOR JSON PATH 
     ) 
     END 
    ) AS QuotedStuffArray, 
    (
     CASE WHEN DatePart(second, GetDate()) % 2 = 1 THEN 
     (
      SELECT * FROM 
      (
       SELECT 'qwerty' AS Stuff 
       UNION ALL 
       SELECT 'zxcvb' AS Stuff 
      ) AS SubSelect 
      FOR JSON PATH 
     ) 
     ELSE 
     (
      SELECT 'asdf' AS Stuff 
      FOR JSON PATH 
     ) 
     END 
    ) AS WhyItMatters, 
    (
     SELECT * FROM 
     (
      SELECT 'qwerty' AS Stuff 
      UNION ALL 
      SELECT 'zxcvb' AS Stuff 
     ) AS SubSelect 
     FOR JSON PATH 
    ) AS ButThisIsFine 
FOR JSON PATH 

这个输出该JSON：

[ 
    { 
     "Greeting": "Hi", 
     "StuffArray": [ 
      { 
       "Stuff": "qwerty" 
      } 
     ], 
     "QuotedStuffArray": "[{\"Stuff\":\"qwerty\"}]", 
     "WhyItMatters": "[{\"Stuff\":\"qwerty\"},{\"Stuff\":\"zxcvb\"}]", 
     "ButThisIsFine": [ 
      { 
       "Stuff": "qwerty" 
      }, 
      { 
       "Stuff": "zxcvb" 
      } 
     ] 
    } 
] 

在此查询，您会在基础对象之外的层次结构中看到四个不同的对象：StuffArray,QuotedStuffArray,WhyItMatters和ButThisIsFine。 StuffArray对象正是我希望我的所有对象看起来像 - 纯JSON没有任何转义。但是，当我开始将SELECT语法放入我的CASE语句中时，我的结果开始引用，如QuotedStuffArray对象所示。所以对于前两个对象，这很好。但我有一个问题，我有时需要执行两个硬编码值的条件UNION，这迫使我将SELECT放入CASE语句中，如WhyItMatters对象所示。 ButThisIsFine对象产生格式化的输出，就像我想WhyItMatters对象被格式化，但它删除了我需要的条件UNION。

我怎样才能得到这最后WhyItMatters对象产生纯粹的JSON没有像ButThisIsFine对象逃脱报价，同时保持在条件UNION陈述？

Answer 1

优化器中对于此查询有一些迷人的行为，我不确定它是否是一个错误。下面的查询将不添加逃避：

SELECT 
    'Hi' AS Greeting, 
    (
     CASE WHEN 1 = 1 THEN (
      SELECT * FROM (
       SELECT 'qwerty' AS [Stuff] 
       UNION ALL 
       SELECT 'zxcvb' AS [Stuff] 
      ) _ 
      FOR JSON PATH 
     ) ELSE (
      SELECT 'asdf' AS [Stuff] 
      FOR JSON PATH 
     ) 
     END 
    ) AS WhyItMatters 
FOR JSON PATH 

的CASE可以被优化掉，这是优化走，而最终的结果是很好的嵌套JSON。但是，如果我们去掉优化东西拿走的能力，它沦为粘贴在一个转义字符串：

SELECT 
    'Hi' AS Greeting, 
    (
     CASE WHEN RAND() = 1 THEN (
      SELECT * FROM (
       SELECT 'qwerty' AS [Stuff] 
       UNION ALL 
       SELECT 'zxcvb' AS [Stuff] 
      ) _ 
      FOR JSON PATH 
     ) ELSE (
      SELECT 'asdf' AS [Stuff] 
      FOR JSON PATH 
     ) 
     END 
    ) AS WhyItMatters 
FOR JSON PATH 

似乎不合逻辑一个查询将导致处理输入JSON和其他的不会，但你去那里。JSON是不是在T-SQL（不像XML）的实际类型，所以我们不能CAST或CONVERT，但JSON_QUERY会做大致相同的事情：

SELECT 
    'Hi' AS Greeting, 
    JSON_QUERY(
     CASE WHEN RAND() = 1 THEN (
      SELECT * FROM (
       SELECT 'qwerty' AS [Stuff] 
       UNION ALL 
       SELECT 'zxcvb' AS [Stuff] 
      ) _ 
      FOR JSON PATH 
     ) ELSE (
      SELECT 'asdf' AS [Stuff] 
      FOR JSON PATH 
     ) 
     END 
    ) AS WhyItMatters 
FOR JSON PATH 

请注意，这也适用，如果参数已JSON（在常量情况下），所以无论添加如何都是安全的。这两种解决方案的

Answer 2

我发现了一种可能的解决方案，但我真的不喜欢它。我发布了我希望有人有更好的解决方案。

在我的UNION的每个分支上使用WHERE声明，对CASE声明的肯定或否定都可以阻止对结果进行“细化”处理。

例如，下面的查询：

SELECT 
    'Hi' AS Greeting, 
    (
     SELECT * FROM 
     (
      SELECT 'asdf' AS Stuff WHERE DatePart(second, GetDate()) % 2 = 0 
      UNION ALL 
      SELECT 'qwerty' AS Stuff WHERE DatePart(second, GetDate()) % 2 = 1 
      UNION ALL 
      SELECT 'zxcvb' AS Stuff WHERE DatePart(second, GetDate()) % 2 = 1 
     ) AS SubSelect 
     FOR JSON PATH 
    ) AS Try1 
FOR JSON PATH 

提供了以下的结果：

[ 
    { 
     "Greeting": "Hi", 
     "Try1": [ 
      { 
       "Stuff": "qwerty" 
      }, 
      { 
       "Stuff": "zxcvb" 
      } 
     ] 
    } 
] 

如果没有更好的可以发现，我可以向前这一招。但是，这似乎是一个难以控制的方法。

Answer 3

我已经测试peformance：

第一 - 通过JSON_QUERY：

declare @i int = 1; 
SELECT 
    JSON_QUERY(
     CASE when @i = 1 THEN 
     (
      SELECT * FROM 
      (
       select textCol AS Stuff from table1 where id % 2 = 0 
       UNION ALL 
       SELECT textCol AS Stuff from table1 where id % 2 <> 0 
      ) AS SubSelect 
      FOR JSON PATH 
     ) 
     ELSE 
     (
      SELECT textCol AS Stuff from table1 
      FOR JSON PATH 
     ) 
     END 
    ) AS WhyItMatters 
FOR JSON path 

给我平均执行时间91ms。

二：

declare @i int = 1; 
SELECT 
    (SELECT * FROM 
     (
      select textCol AS Stuff from table1 where id % 2 = 0 and @i = 1 
      UNION ALL 
      SELECT textCol AS Stuff from table1 where id % 2 <> 0 and @i = 1 
      union all 
      SELECT textCol AS Stuff from table1 where @i <> 1 
     ) AS SubSelect 
     FOR JSON PATH 
    ) AS WhyItMatters 
FOR JSON path 

给我平均执行时间45ms。

table1包含12727行。生成的JSON长度约为1500000个字符。