sql - 左连接ON非空列不能选择非空列

Question

每个表都有一个列 RECNUM。它们是(十进制(28,0)，不为空)。这就是我加入的地方。我想选择 CAUNIT 中的 DESC 列。它是(varchar(28,0)，不为空)。当我运行查询时，我得到:

消息 156，级别 15，状态 1，第 1 行 关键字“DESC”附近的语法不正确。以下是我的查询:

SELECT CDCLSVC.UNIT_ID,CAUNIT.DESC
FROM CDCLSVC
LEFT JOIN CAUNIT
ON CDCLSVC.RECNUM = CAUNIT.RECNUM

Answer 1

问题出在 DESC 列上。在 SQL Server 中，它是 reserved keyword :

Microsoft SQL Server uses reserved keywords for defining, manipulating, and accessing databases. Reserved keywords are part of the grammar of the Transact-SQL language that is used by SQL Server to parse and understand Transact-SQL statements and batches. Although it is syntactically possible to use SQL Server reserved keywords as identifiers and object names in Transact-SQL scripts, you can do this only by using delimited identifiers.

可能的解决方案:

1. 重命名列，例如描述
2. 用[]引用它

您还可以使用别名来避免输入完整的表名称:

SELECT cd.UNIT_ID,ca.[DESC]
FROM CDCLSVC cd 
LEFT JOIN CAUNIT ca
ON cd.RECNUM = ca.RECNUM