Syntax Issue while Declaring select statement into a variable - sql

Question

If I run the select statement its working fine but if I defined into a variable then I am getting syntax error.
Declare #a varchar(2550)
SET #a='
SELECT 'ALTER DATABASE ' + CAST(DB_NAME() AS VARCHAR(50)) + ' MODIFY FILE ( NAME = ' +
QUOTENAME( df.name,'''') + ', NEWNAME = ''' +
QUOTENAME( DB_NAME()) +
+ CASE
WHEN df.type_desc = 'ROWS' AND df.file_id = 1 THEN '.mdf'' )'
WHEN df.type_desc = 'LOG' THEN '_log.ldf'' )'
WHEN df.type_desc = 'ROWS' AND df.file_id != 1 THEN '.ndf'' )'
END
FROM sys.database_files df'
select #a
Error:
Msg 102, Level 15, State 1, Line 38 Incorrect syntax near ' +
CAST(DB_NAME() AS VARCHAR(50)) + '.

Answer 1

It's a combination of typing errors and wrong use of SET and/or SELECT. If I understand you correctly, you may try to use the following statement:
DECLARE #a varchar(2550)
SELECT #a =
'ALTER DATABASE ' +
CAST(DB_NAME() AS VARCHAR(50)) +
' MODIFY FILE ( NAME = ' +
QUOTENAME( df.name,'''') + ', NEWNAME = ''' +
QUOTENAME( DB_NAME()) +
CASE
WHEN df.type_desc = 'ROWS' AND df.file_id = 1 THEN '.mdf'' )'
WHEN df.type_desc = 'LOG' THEN '_log.ldf'' )'
WHEN df.type_desc = 'ROWS' AND df.file_id != 1 THEN '.ndf'' )'
END
FROM sys.database_files df
SELECT #a
As an important note, when you use SELECT #local_variable and the SELECT statement returns more than one value, the variable is assigned the last value that is returned. So if you want to generate a complex statement for all database files, you need to concatenate the returned rows (using FOR XML PATH or STRING_AGG()). In this case, as #GordonLinoff commented, you may declare the #a variable as nvarchar(max):
DECLARE #a nvarchar(max) = N''
SELECT #a = (
SELECT
N'ALTER DATABASE ' +
CAST(DB_NAME() AS VARCHAR(50)) +
N' MODIFY FILE ( NAME = ' +
QUOTENAME( df.name,'''') +
N', NEWNAME = ''' +
QUOTENAME( DB_NAME()) +
CASE
WHEN df.type_desc = 'ROWS' AND df.file_id = 1 THEN N'.mdf'' )'
WHEN df.type_desc = 'LOG' THEN N'_log.ldf'' )'
WHEN df.type_desc = 'ROWS' AND df.file_id != 1 THEN N'.ndf'' )'
END +
N';'
FROM sys.database_files df
FOR XML PATH('')
)
SELECT #a

Answer 2

I think you're looking for something like this
declare #a nvarchar(max);
with file_cte as (
select
N'ALTER DATABASE ' + quotename(db_name()) +
N' MODIFY FILE ( NAME = ' + quotename( df.name,'''') +
N', NEWNAME = ''' + quotename(db_name()) +
case when df.type_desc = N'ROWS' AND df.file_id = 1 then N'.mdf'' )'
when df.type_desc = N'LOG' THEN N'_log.ldf'' )'
when df.type_desc = N'ROWS' AND df.file_id != 1 then N'.ndf'' )' end string
from sys.database_files df)
select #a=concat(string_agg(string, ';'), ';')
from file_cte;
select #a;