why does this Dynamic Sql Statement fail?

Question

This is no any problem:

select COLUMN_NAME,DATA_TYPE,CHARACTER_MAXIMUM_LENGTH,IS_NULLABLE 
from [AdventureWorks2012].INFORMATION_SCHEMA.COLUMNS WHERE table_name='employee';

But, when it moved to a dynamic statement, it always fail:

begin
DECLARE @sqlstatement VARCHAR(MAX);
DECLARE @TableName varchar(max)='employee';

set @sqlstatement='select COLUMN_NAME,DATA_TYPE,CHARACTER_MAXIMUM_LENGTH,IS_NULLABLE
from [AdventureWorks2012].INFORMATION_SCHEMA.COLUMNS WHERE table_name='+@TableName;
print (@sqlstatement);
EXECUTE(@sqlstatement);

end

error says:Invalid column name 'employee'

Answer 1

you should wrap it with single quotes since column table_name is string,

set @sqlstatement='select COLUMN_NAME,DATA_TYPE,CHARACTER_MAXIMUM_LENGTH,IS_NULLABLE
from [AdventureWorks2012].INFORMATION_SCHEMA.COLUMNS WHERE table_name='''+@TableName+'''';