下面的sql语句怎么理解!
前提-->数据库里面表结构:
CREATE TABLE [dbo].[level_about](
[start_score] [int] NOT NULL,
[end_score] [int] NOT NULL,
[level] [nvarchar](5) NULL
) ON [PRIMARY]
CREATE TABLE [dbo].[student_score](
[sno] [int] NOT NULL,
[cno] [int] NOT NULL,
[score] [int] NOT NULL,
[level] [nvarchar](5) NULL CONSTRAINT [DF_student_Score_level] DEFAULT (N'A'),
CONSTRAINT [PK_student_Score] PRIMARY KEY CLUSTERED
(
[sno] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
update [student_score]
set [student_score].[level]=(
select [level_about].[level]
from [level_about]
where [student_score].[score]
between [level_about].[start_score] and [level_about].[end_score])
这上面的sql语句怎么理解,它是怎么执行的。。。。。
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