T-SQL 支持插值字符串吗?
让我们来看一个例子:
SET @query = 'SELECT ' + @somevariable + ' FROM SOME_TABLE'
我希望能够做到这样:
SET @query = 'SELECT {@somevariable} FROM SOME_TABLE'
谢谢回答!
T-SQL 支持插值字符串吗?
让我们来看一个例子:
SET @query = 'SELECT ' + @somevariable + ' FROM SOME_TABLE'
我希望能够做到这样:
SET @query = 'SELECT {@somevariable} FROM SOME_TABLE'
谢谢回答!
感谢@j.f.sebastian指出这些解决方案。可惜xp_sprintf仅支持254个字符,因此在使用长查询时并不理想。FORMATMESSAGE限制在2047个字符,所以足以运行长查询。
我将总结所有解决方案并在一篇文章中呈现,以保持组织性。
使用FORMATMESSAGE很重要的一点是要知道,如果将插值字符串作为第一个参数,则仅支持SQL版本2012及以上,因此我将发布两个带有FORMATMESSAGE的答案:
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)
使用xp_sprintf存储过程需要注意它的字符限制为254个,所以对于较长的查询不是一个好主意。
DECLARE @query AS VARCHAR(100)
,@somevariable as VARCHAR(10) = '[id]'
EXEC xp_sprintf @query OUTPUT, 'SELECT %s FROM SOME_TABLE', @somevariable
sp_addmessage
方法的重要缺点是在多个会话同时执行时不安全,这可能导致一些非常混乱的消息。该技术仍然有用,但应注意不要在需要插值时使用它,因为这将大大增加冲突的可能性。此外,从 SQL Server 2012 开始,有 CONCAT
可以简化字符串拼接而无需在各处添加 CONVERT
。 - Jeroen MostertFORMATMESSAGE(string, ...)
只适用于 SQL Server 2016 (13.x)
。 - KekuSemauSET @query = replace( replace( replace(
'SELECT {@variable1} FROM {@variable2} WHERE {@variable3}'
, '{@variable1}', @variable1 )
, '{@variable2}', @variable2 )
, '{@variable3}', @variable3 )
它具有SQL字符串可读性的优势,同时您可以多次使用相同的变量。 显然,这不是适当的插值,但我喜欢它比FORMATMESSAGE()
选项更好,因为
在 T-SQL 中这不是常规做法,但使用 xp_sprintf 是可行的。
DECLARE @query AS VARCHAR(100)
,@somevariable as VARCHAR(10) = '[id]'
EXEC xp_sprintf @query OUTPUT, 'SELECT %s FROM SOME_TABLE', @somevariable
PRINT @query
我写了两个方便的基于Json的插值函数。一个使用字典样式的Json(键,值对),另一个使用包含每个替换属性的Json对象。
1)数据作为Json对象
例如,给定模板:'嘿,{name}是{age}'
,运行:
SELECT [res4] = [ccgen].[fn_string_interpolation_object]('Hi, {name} is {age}' ,'{"name":"Alice", "age":24}')
...它返回嘿,Alice今年24岁
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:'嘿,{name}今年{age}岁'
,运行:
SELECT [res2] = [ccgen].[fn_string_interpolation]('Hey, {name} is {age}','{"items":[{"key":"name", "value":"Alice"},{"key":"age", "value":"24"}]}')
... 该函数返回 嘿,Alice 今年 24 岁
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需要更多的输入。修改代码并缩短属性名称为“k”(键),“v”(值)和“d”(项),使其更小。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"}]}')
注意:
自然地,这只适用于支持Json的MSSQL版本。同时,不支持转义。例如,无法将{a}作为字面量和替换参数。虽然可以使用转义来添加此功能,但由于我没有使用此功能,因此不能保证其效果。
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];
DECLARE @message VARCHAR(MAX) = 'Some {item} with {count} {collection}.';
SELECT @message = REPLACE(@message, SearchText, ReplaceText)
FROM ( VALUES
('{item}', 'text string'),
('{count}', '3'),
('{collection}', 'variables')
) _ (SearchText, ReplaceText);
CONCAT()
函数。示例 - tinystone