小编典典

可以在MSSQL查询中使用多个JSON_VALUE-s损害性能

sql

我在sql server数据库中有json类型列的表。

Table - SomeTable
Id | Properties
1  | {"field1":"value1", "field2":"value2", "field3":"value3", "field4":"value4"}
2  | {"field1":"value1", "field2":"value2", "field3":"value3", "field4":"value4"}
...|...

我编写了select查询,它分别选择每个字段的值:

SELECT
    JSON_VALUE(Properties, '$.field1') as field1,
    JSON_VALUE(Properties, '$.field2') as field2,
    JSON_VALUE(Properties, '$.field3') as field3,
    JSON_VALUE(Properties, '$.field4') as field4
FROM SomeTable

我在Microsoft的文档中找到了这种方法(https://docs.microsoft.com/zh-cn/sql/relational-
databases/json/json-data-sql-server?view=sql-server-
ver15)

可以在查询中编写许多JSON_VALUE-s损害性能吗?SQL是否对查询中写入的每个JSON_VALUE进行字符串反序列化。


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2021-05-16

共1个答案

小编典典

您可以尝试使用OPENJSON()显式架构,Properties通过一个函数调用(针对四个或更多JSON_VALUE()调用)来解析存储在列中的JSON

桌子:

CREATE TABLE SomeTable (
   Id int,
   Properties varchar(1000)
)
INSERT INTO SomeTable (Id, Properties)
VALUES
   (1, '{"field1":"value1", "field2":"value2", "field3":"value3", "field4":"value4"}'),
   (2, '{"field1":"value1", "field2":"value2", "field3":"value3", "field4":"value4"}')

陈述:

SELECT s.Id, j.*
FROM SomeTable s
CROSS APPLY OPENJSON(s.Properties) WITH (
   field1 varchar(100) '$.field1',
   field2 varchar(100) '$.field2',
   field3 varchar(100) '$.field3',
   field4 varchar(100) '$.field4'
) j

结果:

Id  field1  field2  field3  field4
----------------------------------
1   value1  value2  value3  value4
2   value1  value2  value3  value4

另外请注意,的结果JSON_VALUE()是type的标量值nvarchar(4000)。使用OPENJSON()显式架构,您可以为返回的列定义适当的数据类型。

2021-05-16