在 SQL Select 中连接字符串

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

未在内容值列的末尾添加字符“=”。我也试过：

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

同样的问题...字符串末尾没有添加字符'='。

我错过了什么？

Answer 1

The character '=' is not being added at the end of the column

当然是。 SSMS 可能正在截断该值。但是你不应该首先在末尾添加'='。这是 base64 规范的一部分，xml.value() 将根据需要添加“=”或“==”来填充值。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===
*/

这是一个比较 .NET 和 SQL 服务器的 base64 编码的示例：

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);
            }
        }
    }
}

在 SQL Select 中连接字符串

Concat string in SQL Select

tsql

sql-server

concat