为什么触发器在使用'插入'表中的字段时尝试插入NULL值？

Question

我必须将在MSSQL中完成的更改与远程MySQL数据库同步。要同步的更改将发票和用户添加到系统中。远程服务器不会总是可以访问，所以我试图建立一种日志表来存储在MSSQL中完成的更改。

这里是一个完全正常触发：

CREATE TRIGGER [dbo].[dokument_insert] 
    ON [dbo].[dokument] 
    AFTER INSERT 
AS 
BEGIN 
    SET NOCOUNT ON; 
    INSERT INTO [bcg_ekodu].[dbo].[sync_stack] (event,sql, table_name, import_priority) 
     SELECT 
      'INSERT', 
      'INSERT INTO bills SET 
       date = "'+CONVERT(VARCHAR(19),dok_kuup,120)+'", 
       total = "'+CAST(kokkusum AS nvarchar)+'", 
       number = "'+RTRIM(dok_nr)+'", 
       created = "'+CONVERT(VARCHAR(19),savetime,120)+'", 
       rounded = "'+CAST(ymardus AS nvarchar)+'", 
       currency = "'+CAST(valuuta AS nvarchar)+'", 
       due_date = "'+CONVERT(VARCHAR(19),tasupaev,120)+'", 
       pk_joosep = "'+CAST(dok_kood AS nvarchar)+'", 
       joosep_hankija = "'+CAST(hankija AS nvarchar)+'"; 
      UPDATE 
       bills, users, companies 
      SET 
       bills.user_id = users.id, 
       bills.imported = NOW() 
      WHERE 
       bills.imported IS NULL 
       AND companies.id = users.company_id 
       AND companies.pk_joosep = 10 
       AND bills.user_id = users.pk_joosep', 
      'bills', 
      '200' 
     FROM inserted 
END 

，每天一个行插入“库门”表时插入行“sync_stack”表。 'sql'列将包含一个SQL，以在另一个（MySQL）数据库中创建相同类型的行。

但这触发不工作：

CREATE TRIGGER [dbo].[klient_insert] 
    ON [dbo].[klient] 
    AFTER INSERT 
AS 
BEGIN 
    SET NOCOUNT ON; 
    INSERT INTO [bcg_ekodu].[dbo].[sync_stack] (event,sql, table_name, import_priority) 
     SELECT 
      'INSERT', 
      'INSERT INTO users SET 
       username =10'+CAST(kl_kood as nvarchar)+', 
       password = NULL, 
       name ="'+LTRIM(RTRIM(kl_nimi))+'", 
       email ="'+CAST(LTRIM(RTRIM(kl_email)) as nvarchar)+'", 
       reference_no ="'+CAST(LTRIM(RTRIM(kl_viide)) as nvarchar)+'", 
       phone ="'+CAST(LTRIM(RTRIM(kl_tel1)) as nvarchar)+'", 
       logins ="'+CAST(0 as nvarchar)+'", 
       last_login = NULL, 
       created ="'+CONVERT(VARCHAR(19),savetime,120)+'", 
       updated = NULL, 
       deleted ="0", 
       address ="'+CAST(LTRIM(RTRIM(kl_aadr1)) as nvarchar)+'",  
       pk_joosep ="'+CAST(kl_kood as nvarchar)+'"', 
      'users', 
      '210' 
     FROM inserted 
END 

虽然上面的SQL创建触发器执行完成就好了，当我尝试了一些行插入到“触发”表中，我得到的以下错误：

No row was updated. 

The data in row 175 was not committed. 
Error Source: .Net SqlClient Data Provider. 
Error Message: Cannot insert the value NULL into column 'sql', table 'mydb.dbo.sync_stack'; column does not allow nulls. INSERT fails. 

The statement has been terminated. 

Correct the errors and retry or press ESC to cancel the change(s). 

• 如果我删除此触发器，则不会出现此错误。
• 如果我只为'sql'列插入纯文本，它按预期工作。
• 如果我使用插入行中的任何字段，即使只是一个文本字段，它也会再次失败。
• 如果我在'sql'列允许NULL值，插入行成功，但我'SQL'列中获得NULL值。

如何使第二个触发器按预期工作呢？

Answer 1

串联为NULL任何值为NULL：

select 'test' + NULL 

结果无效，你应该使用类似的东西为你列：

select isnull(column, '') 

这将导致一个空字符串。

Answer 2

我怀疑至少有一个插入到你的SQL语句中的值是NULL。您可以使用COALESCE（例如

username =10'+COALESCE(CAST(kl_kood as nvarchar), '')+', 

当然，你不应该声明nvarchar没有指定长度，对不对？

http://sqlblog.com/blogs/aaron_bertrand/archive/2009/10/09/bad-habits-to-kick-declaring-varchar-without-length.aspx