SQL 内插字符串

Question

T-SQL是否支持内插字符串？

举个例子：

SET @query = 'SELECT ' + @somevariable + ' FROM SOME_TABLE'

我希望能够做这样的事情：

SET @query = 'SELECT {@somevariable} FROM SOME_TABLE'

感谢您的回答！

Answer 1

在 T-SQL 中这不是一种常见的做事方式，但在 xp_sprintf

中是可能的

    DECLARE  @query AS VARCHAR(100)
            ,@somevariable as VARCHAR(10) = '[id]'
    EXEC xp_sprintf @query OUTPUT, 'SELECT %s FROM SOME_TABLE', @somevariable

    PRINT @query

Answer 2

感谢@j.f.sebastian 指出这些解决方案。遗憾的是 xp_sprintf 被限制为 254 个字符，因此在使用长查询时这并不理想。 FORMATMESSAGE 限制为 2047 个字符，因此足以运行长查询。

为了让事情井井有条，我会将解决方案的所有内容汇总在一个 post 中。

答案 1：

使用 FORMATMESSAGE 重要的是要知道，使用内插字符串作为第一个参数，它仅支持 SQL 2012 及更高版本，所以我将 post 2 个答案格式信息：

SQL 版本 >= 2012:

SET @query = FORMATMESSAGE('SELECT %s FROM SOME_TABLE', @somevariable);

SQL 版本 < 2012:

EXEC sp_addmessage 50001, 16, 'SELECT %s FROM SOME_TABLE', NULL, NULL, 'replace'
SET @query = FORMATMESSAGE(50001, @somevariable)

答案 2：

使用 xp_sprintf 存储过程需要注意，它限制在 254 个字符以内，因此对于长查询来说不是一个好主意。

DECLARE  @query AS VARCHAR(100)
        ,@somevariable as VARCHAR(10) = '[id]'
EXEC xp_sprintf @query OUTPUT, 'SELECT %s FROM SOME_TABLE', @somevariable

Answer 3

我喜欢为我的动态 SQL 这样做，所以我 wrote a function for SQL Server 2017+（使用 STRING_AGG 和 JSON_VALUE）。它可以被重写以使其与旧版本兼容。

以下是 link 死亡时的文本：

CREATE OR ALTER FUNCTION [Tools].[StringInterpolation] 
 (@Template VARCHAR(MAX)
, @JSON_Row NVARCHAR(MAX))
/*
This function replaces a string template with actual values from a JSON-formatted row
The table returns a single column: FormattedString

** Requires SQL Server 2017+ for STRING_AGG (could be rewritten using XML PATH)
** Requires SQL Server 2016+ for JSON_VALUE (maybe you could use XML)

EXAMPLE: 
SELECT *
FROM (SELECT [Name] = 'Steven', Adjective = 'internet person',        Verb = 'writes helpful(?) SQL functions') [d]
CROSS APPLY Tools.StringInterpolation ('{Name} is a {Adjective} who {Verb}.', (SELECT [d].* FOR JSON PATH))

Name   | Adjective              | Verb                            | FormattedString
-------+------------------------+---------------------------------+-----------------------------------------------------------------
Steven | internet person        | writes helpful(?) SQL functions | Steven is a internet person who writes helpful(?) SQL functions.
*/ 
RETURNS TABLE
  RETURN
  WITH [CTE_10]
       AS (SELECT [Number]
           FROM(VALUES (1), (1), (1), (1), (1), (1), (1), (1), (1), (1) ) [v]([Number])),
       -------------------
       /* 100 rows (all 1s) */
       [CTE_100]
       AS (SELECT [Number] = 1
           FROM [CTE_10] [a]
                CROSS JOIN [CTE_10] [b]),
       -------------------
       /* 1,000,000 rows max (all 1s) */
       [CTE_1000000]
       AS (SELECT [Number] = 1
           FROM [CTE_100] [a]
                CROSS JOIN [CTE_100] [b]
                CROSS JOIN [CTE_100] [c]),
       -------------------
       /* Numbers "Table" CTE: 1) TOP has variable parameter = DATALENGTH(@Template), 2) Use ROW_NUMBER */
       [CTE_Numbers]
       AS (SELECT TOP (ISNULL(DATALENGTH(@Template), 0)) 
                  [Number] = ROW_NUMBER() OVER(ORDER BY (SELECT NULL) )
           FROM [CTE_1000000]),
       -------------------

       /* This is tricky. Get each start of each variable or non-variable
          Variables look like {...}
          Non-variables look like }...{ (i.e. the bits between the variables) */
       [CTE_Start]
       AS (SELECT [Type] = 'Text'
                , [Start] = 1
           UNION ALL
           SELECT [Type] = IIF([Char] = '{', 'Variable', 'Text')
                , [Start] = [Number] + 1 -- start *after* the { or }
           FROM [CTE_Numbers]
                CROSS APPLY (SELECT [Char] = SUBSTRING(@Template, [Number], 1)) [c]
           WHERE [Char] IN ( '{', '}' ) ),
       -------------------

       /* Pair each "start" with the next to find indicies of each substring */
       [CTE_StringIndicies]
       AS (SELECT [Type]
                , [Start]
                , [End] = ISNULL(LEAD([Start]) OVER(
                                 ORDER BY [Start]) - 1, DATALENGTH(@Template) + 1)
           FROM [CTE_Start]),
       -------------------

       /* Get each substring */
       [CTE_Variables]
       AS (SELECT [Start]
                , [Type]
                , [SubString] = SUBSTRING(@Template, [Start], [End] - [Start])
           FROM [CTE_StringIndicies]),
       -------------------

       /* If it's a variable, replace it with the actual value from @JSON_Row
          Otherwise, just return the original substring */
       [CTE_Replacements]
       AS (SELECT [Start]
                , [Substring] = IIF([Type] = 'Variable', JSON_VALUE(@JSON_Row, '$[0].' + [Substring]), [Substring])
           FROM [CTE_Variables])
       -------------------

       /* Glue it all back together */
       SELECT [FormattedString] = STRING_AGG([Substring], '') WITHIN GROUP (ORDER BY [Start])
       FROM [CTE_Replacements];

Answer 4

当你的字符串很长时为了便于阅读，我喜欢这样做：

SET @query = replace( replace( replace( 
               'SELECT {@variable1} FROM {@variable2} WHERE {@variable3}'
               , '{@variable1}', @variable1 )
               , '{@variable2}', @variable2 )
               , '{@variable3}', @variable3 )

它具有 SQL 字符串的可读性优势，而且您可以多次使用同一个变量。显然这不是正确的插值，但我比 FORMATMESSAGE() 选项更喜欢它，因为

它没有长度限制。无论如何，谁会编写短于 2047 个字符的查询？！ ;)
它支持命名占位符，而不仅仅是有序的占位符
任何版本的 SQL Server
您可以多次使用同一个占位符

Answer 5

编写了 2 个方便的基于 Json 的插值函数。一个使用字典样式 Json（键，值对），另一个 Json 对象包含每个替换的属性。

1) 数据作为 Json 对象

例如，给定模板：'Hey, {name} is {age}'、运行：

SELECT [res4] = [ccgen].[fn_string_interpolation_object]('Hi, {name} is {age}' ,'{"name":"Alice", "age":24}')

... returns Hey, Alice is 24

CREATE OR ALTER FUNCTION [CcGen].[fn_string_interpolation_object](
   @template NVARCHAR(4000), @data_json NVARCHAR(4000)) RETURNS NVARCHAR(4000) AS

   /*
   =============================================
   C# or Java like string interpolation brought to TSQL.

   example - copy to run proc
   -----------------------
   --property names must match those in template. Same as a dynamic object in C#

   SELECT [res4] = [ccgen].[fn_string_interpolation_object]('Hi, {name} is {age}' ,'{"name":"Alice", "age":24}')

   -- returns
   Hi, Alic is 24
   =============================================
   */

BEGIN
   SELECT @template = REPLACE(@template ,'{' + [key] + '}' ,[value]) FROM OPENJSON(@data_json);
   RETURN @template;
END;

2) 数据作为 Json 字典 例如，给定模板：'Hey, {name} is {age}'、运行:

SELECT [res2] = [ccgen].[fn_string_interpolation]('Hey, {name} is {age}','{"items":[{"key":"name", "value":"Alice"},{"key":"age", "value":"24"}]}')

... returns Hey, Alice is 24

CREATE OR ALTER FUNCTION [CcGen].[fn_string_interpolation](
   @template NVARCHAR(4000), 
   @key_value_json NVARCHAR(4000)) RETURNS NVARCHAR(4000) AS

   /*
   =============================================
   C# or Java like string interpolation brought to TSQL.
   
   example - copy to run proc
   -----------------------

   DECLARE @json NVARCHAR(2048) = N'{
    "items": [
        {
            "key": "A",
            "value": "a1"
        },
        {
            "key": "B",
            "value": "b2"
        },
        {
            "key": "C",
            "value": "c3"
        }
    ]
}';

   DECLARE @template NVARCHAR(4000) = 'message:= A:{A}, B:{B}, C:{C}'
   select res = ccgen.fn_string_interpolation(@template, @json)

   -- returns
   formatted 3 = A:a1, B:b2, C:c3
   =============================================
   */

BEGIN
   SELECT @template = REPLACE(@template ,'{' + [key] + '}' ,[value]) FROM OPENJSON(@key_value_json ,'$.items') WITH ( [key] VARCHAR(200) '$.key', [value] VARCHAR(4000) '$.value' );
   RETURN @template;
END;

提示：Json 需要多输入一点。修改代码并将属性名称缩短为“k”（键）、“v”（值）和“d”（项目）以使其变小。然后调用更整洁：

SELECT [res2] = [ccgen].[fn_string_interpolation]('Hey, {name} is {age}','{"d":[{"k":"name", "v":"Alice"},{"k":"age", "v":"24"}]}')

备注：

当然这只适用于支持 Json 的 MSSQL 版本。也不支持转义。例如，不可能将 {a} 同时作为文字参数和替换参数。这可以使用转义来添加，但不能保证努力，因为我没有用到这个功能。

SQL 内插字符串

SQL Interpolated Strings

sql

tsql

string

interpolation

答案 1：

答案 2：