MS SQL语法SET与SELECT

Question

I'm trying to follow the following SQL Query (Partial code):

DECLARE @name VARCHAR(50)       -- database name  
DECLARE @path VARCHAR(256)      -- path for backup files  
DECLARE @fileName VARCHAR(256)  -- filename for backup  
DECLARE @fileDate VARCHAR(20)   -- used for file name 

SET @path = 'C:\Backup\'
SET @fileDate = CONVERT(VARCHAR(20),GETDATE(),112) 

DECLARE db_cursor CURSOR FOR  
    SELECT name 
    FROM MASTER.dbo.sysdatabases 
    WHERE name NOT IN ('master','model','msdb','tempdb')

My questions:

1. Why is @path using SET , while @fileDate using SELECT ?
2. Why isn't @fileDate SET as well?

Answer 1

Since its a backup query

SET @path = 'C:\\Backup\\' --- It means we are taking backup on a static path

SELECT @fileDate = CONVERT(VARCHAR(20),GETDATE(),112) --- filedate will be dynamic due to getdate() and it may be used in the .bak file naming convention so thats why mostly we use select for @filedate

eg if performing a backup daily once.

then it may provide the backup on static path (@path) and backup with naming convention eg ____bkup_20160519.bak

here 20160519 is @filedate which will change daily

Let me know if you need more idea regarding it.

Answer 2

In your exmaple either Set or Select is same. Select is used to selected values to more than one variable like shown below

This works

SELECT @fileDate = CONVERT(VARCHAR(20),GETDATE(),112) ,@path = 'C:\Backup\'

but this does not work

set @fileDate = CONVERT(VARCHAR(20),GETDATE(),112) ,@path = 'C:\Backup\'

Answer 3

In your case I do not see a reason. One reason I would use Select over Set if I want to set multiple values at once.

DECLARE @name VARCHAR(50) -- database name  
DECLARE @path VARCHAR(256) -- path for backup files  
DECLARE @fileName VARCHAR(256) -- filename for backup  
DECLARE @fileDate VARCHAR(20) -- used for file name 

--SET @path = 'C:\Backup\'  

Select  @path = 'C:\Backup\' , @fileDate = CONVERT(VARCHAR(20),GETDATE(),112)

Select @Path, @FileDate