Как понять, какой столбец неверный

using LinqToDB;
using LinqToDB.Data;
using LinqToDB.DataProvider.SqlServer;
using Microsoft.Data.SqlClient;
 
const string ConnString = "...";
 
// INSERT ... WHEN NOT EXISTS
 
TearUp();
 
try
{
    using var conn = new SqlConnection(ConnString);
    conn.Open();
 
    var sql =
        """
        insert into UniqTest (email)
        select * from
        (
            values (N'test@test.com')
        ) as v(email)
        where not exists
        (
            select 1 from UniqTest where email = N'test@test.com'
        )
        """;
 
    using var cmd = new SqlCommand(sql, conn);
 
    System.Console.WriteLine("count: " + cmd.ExecuteNonQuery()); // 1
    System.Console.WriteLine("count: " + cmd.ExecuteNonQuery()); // 0
}
finally
{
    TearDown();
}
 
// MERGE INTO
 
TearUp();
 
try
{
    using var conn = new SqlConnection(ConnString);
    conn.Open();
 
    var sql =
        """
        merge UniqTest as t
        using 
        (
            values (N'test@test.com')
        ) as s(email)
        on t.email = s.email
        when not matched by target then
        insert (email) values(s.email);
        """;
 
    using var cmd = new SqlCommand(sql, conn);
 
    System.Console.WriteLine("count: " + cmd.ExecuteNonQuery()); // 1
    System.Console.WriteLine("count: " + cmd.ExecuteNonQuery()); // 0
}
finally
{
    TearDown();
}
 
// LINQ2DB: INSERT ... WHEN NOT EXISTS
 
TearUp();
 
try
{
    using var conn = new DataConnection(
        new DataOptions()
            .UseConnectionString(ConnString)
            .UseSqlServer(SqlServerVersion.v2022, SqlServerProvider.MicrosoftDataSqlClient)); 
 
    var uniqTest  = conn.GetTable<UniqTest>();
    var construct = new [] { new UniqTest{ Email = "test@test.com" }}.AsQueryable(conn);
 
    var query = construct
        .Where(x => !uniqTest.Any(y => y.Email == x.Email))
        .Into(uniqTest);
 
    System.Console.WriteLine("count: " + query.Insert()); // 1
    System.Console.WriteLine("count: " + query.Insert()); // 0
}
finally
{
    TearDown();
}
 
// LINQ2DB: MERGE INTO
 
TearUp();
 
try
{
    using var conn = new DataConnection(
        new DataOptions()
            .UseConnectionString(ConnString)
            .UseSqlServer(SqlServerVersion.v2022, SqlServerProvider.MicrosoftDataSqlClient)); 
 
    var construct = new [] { new UniqTest{ Email = "test@test.com" }};
 
    var query = conn.GetTable<UniqTest>()
        .Merge()
        .Using(construct)
        .On((s, t) => t.Email == s.Email)
        .InsertWhenNotMatched();
 
    System.Console.WriteLine("count: " + query.Merge()); // 1
    System.Console.WriteLine("count: " + query.Merge()); // 0
}
finally
{
    TearDown();
}
 
void TearUp()
{
    using var conn = new SqlConnection(ConnString);
    using var cmd = new SqlCommand("create table UniqTest(email nvarchar(100), constraint uc_UniqTest_email unique (email))", conn);
    conn.Open();
    cmd.ExecuteNonQuery();
}
 
void TearDown()
{
    using var conn = new SqlConnection(ConnString);
    using var cmd = new SqlCommand("drop table UniqTest", conn);
    conn.Open();
    cmd.ExecuteNonQuery();
}
 
// LINQ2DB
class UniqTest
{
    public string Email { get; set; }
}