SQL Select中的Concat字符串

Question

我有以下TSQL：

SELECT 
    Id, 
    CAST('' as XML).value('xs:base64Binary(sql:column("Content"))', 'NVARCHAR(MAX)') + '=' as Content, 
    Name
FROM Files
ORDER BY Id

字符'='未添加到列Content值的末尾。我也尝试过：

SELECT 
    Id, 
    CONCAT(CAST('' as XML).value('xs:base64Binary(sql:column("Content"))', 'NVARCHAR(MAX)'), '=') as Content, 
    Name
FROM Files
ORDER BY Id

相同问题...字符'='未添加到字符串的末尾。

我想念什么？

Answer 1

没有在列末尾添加字符'='

确定。 SSMS可能会截断该值。但是，您不应该首先在末尾添加“ =”。这是base64规范的一部分，并且xml.value（）将添加'='或'=='以根据需要填充该值。在末尾添加“ =”将产生无效的base64字符串，例如：

use tempdb
go
drop table if exists Files
go
create table Files(id int primary key, name varchar(200), Content varbinary(max))

go
insert into Files(id,name,Content) values (1,'1',0x9789798d7987907a09797a987908790787897b0987d9087097e09879087d907907097097a0c0909890809789798798789798707097090)


SELECT 
    Id, 
    CAST('' as XML).value('xs:base64Binary(sql:column("Content"))', 'NVARCHAR(MAX)') + '=' as Content, 
    Name
FROM Files
ORDER BY Id

/*
CXiXmNeYeQegl5eph5CHkHh4l7CYfZCHCX4Jh5CH2QeQcJcJegwJCYkICXiXmHmHiXmHBwlwkA===
*/

这里是一个示例，用于比较.NET和SQL Server的base64编码：

using System;
using System.Data;
using System.Linq;
using System.Data.SqlClient;

namespace netcore3test
{
    class File
    {
        public byte[] Content { get; set; }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var maxLen = 1024 * 1024;

            using var con = new SqlConnection("server=localhost;database=tempdb;integrated security=true");
            con.Open();

            var cmd = con.CreateCommand();
            cmd.CommandText = @"

with q as (select @buf Content)
select CAST('' as XML).value('xs:base64Binary(sql:column(""Content""))', 'NVARCHAR(MAX)') base64string
from q

";
            var pBuf = cmd.Parameters.Add("@buf", SqlDbType.VarBinary, -1);

            var rand = new Random(0);
;
            for (int len = 0; len < maxLen; len++)
            {
                var buf = new byte[len];
                rand.NextBytes(buf);
                pBuf.Value = buf;

                var netBase64 = Convert.ToBase64String(buf);
                var sqlBase64 = (string)cmd.ExecuteScalar();
                var json = @$"{{""Content"" : ""{sqlBase64}"" }}";
                var  File = System.Text.Json.JsonSerializer.Deserialize<File>(json);
                var sqlBuf = File.Content;

                if (!buf.SequenceEqual(sqlBuf) || netBase64 != sqlBase64)
                {
                    Console.WriteLine($"Fail {netBase64} {sqlBase64}");
                }
                Console.WriteLine(sqlBase64);
            }
        }
    }
}