JSON_VALUE for SQL Server 2012?

问题

I want to extract values from a JSON string in SQL. Started to write a function to do so but then I thought "surely someone else has already done this?". I was super excited when I saw there is a JSON_VALUE function in SQL Server now... but then sorely disappointed when I realized it wasn't added until 2016. :(

So... I am in the middle of writing my own version of this function. I'm certain it will seem to work at first, and then I will get errors occasionally until I perfect it over time.

But I'm hoping someone has already gotten a head start on this and worked out a few of the kinks that I will certainly overlook in my first draft... and hoping someone here can point me to it?

回答1:

Well since it seems no one has had anything to offer yet, here is the code I've written so far. Maybe it will help the next person in my shoes. I decided to go with separate functions depending on the type of value I'm retrieving. Of special note is that the date function is for retrieving a value that is the number of milliseconds since 1970, and the decimal function has a parameter to specify whether the value is quoted or not.

create function [dbo].[GetJsonDateValue](@Key varchar(100), @data nvarchar(max))
returns datetime
as
begin
    declare @keyIdx int = charindex(@Key, @data)
    declare @valueIdx int = @keyIdx + len(@Key) + 2 -- +2 to account for characters between key and value
    declare @termIdx int = charindex(',', @data, @keyIdx)

    -- In case it's last item in an object
    if @termIdx = 0
    set @termIdx = charindex('}', @data, @keyIdx)

    declare @valueLength int = @termIdx - @valueIdx
    declare @secondsSince1970 bigint = cast(substring(@data, @valueIdx, @valueLength) as bigint) / 1000

    declare @retValue datetime = dateadd(s, @secondsSince1970, '19700101')
    return @retValue
end
GO

CREATE function [dbo].[GetJsonDecimalValue](@Key varchar(100), @data nvarchar(max), @quoted bit)
returns decimal(9,2)
as
begin
    declare @keyIdx int = charindex(@Key, @data)
    declare @valueIdx int = @keyIdx + len(@Key) + 2 -- +2 to account for characters between key and value
            + case when @quoted = 1 then 1 else 0 end -- +1 more for quote around value if present
    declare @termIdx int = charindex(case @quoted when 1 then '"' else ',' end, @data, @valueIdx)

    -- In case it's last item in an object and not quoted
    if @quoted = 0 and @termIdx = 0
    set @termIdx = charindex('}', @data, @keyIdx)

    declare @valueLength int = @termIdx - @valueIdx

    if @valueLength = 0
    return null

    declare @retValue decimal(9,2) = cast(substring(@data, @valueIdx, @valueLength) as decimal(9,2))
    return @retValue
end
GO

CREATE function [dbo].[GetJsonStringValue](@Key varchar(100), @data nvarchar(max))
returns varchar(max)
as
begin
    declare @keyIdx int = charindex(@Key, @data)
    declare @valueIdx int = @keyIdx + len(@Key) + 3 -- +3 to account for characters between key and value
    declare @termIdx int = charindex('"', @data, @valueIdx)

    declare @valueLength int = @termIdx - @valueIdx
    declare @retValue varchar(max) = substring(@data, @valueIdx, @valueLength)
    return @retValue
end
GO

回答2:

First of all, thank you @BVernon - your answer got me on right track. I have improved version of this - it is capable of:

returning strings, numbers or null and handle
handles JSON quote escaping
a bit better/robust finding - in case key is part of some other string value, it searches by "key":, not just by key.

CREATE FUNCTION [dbo].[GetJsonValue](@key varchar(100), @data nvarchar(max))
RETURNS nvarchar(max)
AS
BEGIN
  DECLARE @keyJson varchar(105) = '"' + @key+ '":'
  DECLARE @keyIdx int = CHARINDEX(@keyJson, @data)
  IF @keyIdx = 0 RETURN null

  DECLARE @valueIdx int = @keyIdx + LEN(@keyJson)
  DECLARE @termIdx int = CHARINDEX('"', @data, @valueIdx)

  IF @termIdx <> 0 BEGIN
    SET @valueIdx = @valueIdx + 1
    SET @termIdx = CHARINDEX('"', @data, @valueIdx)

    -- Overcome JSON qoute escape
    WHILE SUBSTRING(@data, @termIdx-1, 1) = '\'
    BEGIN
      SET @termIdx = CHARINDEX('"', @data, @termIdx + 1)
    END
  END ELSE BEGIN
    SET @termIdx = CHARINDEX(',', @data, @valueIdx)
    IF @termIdx = 0 SET @termIdx = CHARINDEX('}', @data, @valueIdx)
  END

  IF @termIdx = 0 RETURN null

  -- Replace escapte quote before return value
  RETURN REPLACE(SUBSTRING(@data, @valueIdx, @termIdx - @valueIdx), '\"', '"')
END

It still have limitations:

handling nested objects is not supported, moreover it could give false results, if the key is somewhere deep in object
does not support anything but returning scalar value by key

These are some tests:

-- These work just fine
print [dbo].[GetJsonValue]('foo', '{"foo":"bar"}')
print [dbo].[GetJsonValue]('foo', '{"foo":"Quoted \"bar\""}')
print [dbo].[GetJsonValue]('foo', '{"foo":55}')
print [dbo].[GetJsonValue]('foo', '{"foo":null}')
print [dbo].[GetJsonValue]('foo', '{"a":"foo","foo":"baz"}')   -- no false positive

-- CANNOT HANDLE SPACES
print [dbo].[GetJsonValue]('foo', '{"foo":   "bar"}')

-- FALSE POSITIVE!!!
print [dbo].[GetJsonValue]('foo', '{"nested:{"foo":123}}')
print [dbo].[GetJsonValue]('foo', '[{"foo":123}]')

Output is:

bar
Quoted "bar"
55
null
baz

123
123

来源：https://stackoverflow.com/questions/52732623/json-value-for-sql-server-2012

标签

json

sql-server-2012