如何用不同的列但按一个特定列排序的UNION ALL SELECT MySQL查询？

Question

One problem is that they have different named columns

So for example

Table 1
- id
- value_a
- value_b

Table 2
- sid
- value_c
- value_d

I need something like

SELECT id,value_a,value_b AS results FROM table_1 UNION ALL SELECT sid,value_c,value_d AS results FROM table_2 ORDER BY value_a/value_c LIMIT 30

I realize the value_a/value_c isn't what I'd actually do but that's what I mean.

Right now I am able to get the different columns and order alphabetically, I'm just trying to avoid querying again to first figure out which table the current row came from and then grabbing the rest, right now what I've got is

SELECT value_a AS name FROM table_1 UNION ALL SELECT value_c AS name FROM table_2 ORDER BY name LIMIT 30

Can I do what I'm trying to do? I've been going through a bunch of stack overflow threads, not really getting it to work.

edit: this might be what I want

Using union and order by clause in mysql

edit:

The answer I came to from posts here and from other stackoverflow posts:

So you've got your two tables.

To select from both and order by a specific column and also echo out each specific column:

SELECT id AS id, value_a AS value_1, value_b AS value_2, 1 as tblname FROM Table_1 UNION ALL SELECT sid as id, value_c as value_1, value_d as value_2, 2 as tblname FROM Table_2 ORDER BY value_1 LIMIT 30

Then you can write a catch like this:

if ($row['tblname'] === "1") {
  // echo out / do stuff to this specific set of columns
  echo $row['value_1']; // echos out value_a
}
else if ($row['tblname'] === "2") {
  // echo out / do stuff to this specific set of columns
  echo $row['value_1']; // echos out value_c
}

Not saying this is the best route, but this single query that gets 30 rows is better than the same command but using more than one query becoming 31 queries (1 query every time you want to get the data knowing what you're looking for in what table)

Answer 1

Something like this?

SELECT
    t.id
    t.results
from
    (
        SELECT 
            id
            ,value_a
            ,value_b AS results 
        FROM table_1 
        UNION ALL 
        SELECT 
            sid
            ,value_c
            ,value_d AS results 
        FROM table_2 
    ) as t
ORDER BY results 
LIMIT 30

Answer 2

Not exactly sure about your requirements. But I assume you need to order the columns alphabetically after the union all and still be able to tell which table the row is actually from.

Correct me if I am wrong.

I would go with a query like this:

SELECT value_a AS name, 1 as tblname FROM table_1 
UNION ALL 
SELECT value_c AS name, 2 as tblname FROM table_2 
ORDER BY name 

This will display the table no accordingly.

To allow value_b from table_1 and value_d from table_2 to be displayed in separate columns:

SELECT value_a AS name, value_b, null as value_d, 1 as tblname FROM table_1 
UNION ALL 
SELECT value_c AS name, null as value_b, value_d, 2 as tblname FROM table_2 
ORDER BY name