是否可以将表别名附加到列名以找出列的来源？

Question

I have a query that I'm trying to rework that has over 1,000 columns when I select * FROM several tables. I want to know if there is a way in SQL to tag the column alias with the table alias so i can know from which table the columns are from. It looks like the following:

SELECT *
FROM table1 t1
join table2 t2
join table3 t3
join table4 t4

Current column output: id, id, id, id, name, name, name, name, order, order, order, order

Desired Column output: t1.id, t1.name, t1.order, t2.id, t2.name, t2.order,t3.id, t3.name, t3.order, t4.id, t4.name, t4.order

this is a very simple example but you can imagine trying to fish out the column you need of a sea of 1,000 columns trying to figure out what table it came from! Any ideas??

Answer 1

You have to assign non-default column aliases manually:

select t1.id as t1_id, t1.name as t1_name, t1.order as t1_order, 
       t2.id as t2_id, t2.name as t2_name, t2.order as t2_order, 
       . . .

You might find that a spreadsheet or query can help, if you have a lot of columns.

Answer 2

Some products may have exceptions, but generally no, you can't do that. You either have to use wildcards ( SELECT * ) or specify the columns you wish returned by full and complete name.

If you specify columns, you can "alias" them, set the column name to something other than the source name. For example (psuedo-code, leaving out the "ON" clause):

SELECT
   T1.Id  as  T1_Id
  ,T2.Id  as  T2_Id
 from table1  T1
 join table2  T2

Note that you can combine table aliases with wildcards. For example:

SELECT
   T2.*
 from table1  T1
 join table2  T2
 join table3  T3
 join table4  T5

will return all the columns from table2, and only from table2. This might help in revising your query by getting a list of the available columns in each table.

Answer 3

I'm not aware of a way to prefix each column with the column alias. However I do know how you could easily break the columns into groups that would allow you to figure out which table each column comes from.

   SELECT 'T1' as [Table1]
   ,  t1.*
   ,  'T2' as [Table2]
   ,  t2.*
   ,  'T3' as [Table3]
   ,  t3.*
   ,  t4.* as [Table4]
   ,  t4.*
   ,  'T5' as [Table5]
   ,  t5.*
   FROM table1 t1
   join table2 t2
   join table3 t3
   join table4 t4

This would break out the columns into groups by table and it would break a little bookmark before and after each group to help you understand where they're coming.

I know not exactly what you asked for but I believe it would help you a lot in figuring out what's from what tables.

Your other option is as others have said and specifiying the prefix on every column which it sounds like you don't want to do. However it can be a lot quicker to do this if you drag the columns from the Object Explorer - and use ALT-SHIFT to add the prefix to each column.

Here's an article about copying columns from object explorer - https://www.qumio.com/Blog/Lists/Posts/Post.aspx?ID=56

Her's an article about adjusting code using ALT+SHIFT - https://blogs.msdn.microsoft.com/sql_pfe_blog/2017/04/11/quick-tip-shiftalt-for-multiple-line-edits/

The first method would take less than a method, the 2nd method I could see taking less than 10 minutes even for 1,000 columns.