如何对多个查询的结果进行排序？

Question

我有一个查询由三个select条款是这样的：

select id, colors from table1 
    union all 
select id, numbers from table2 
    union all 
select id, names from table3 

另外这里的表结构：

// table1    // table2    //table3 
+----+--------+  +----+---------+  +----+-------+ 
| id | colors |  | id | numbers |  | id | names | 
+----+--------+  +----+---------+  +----+-------+ 
| 1 | red |  | 1 | ten  |  | 1 | jack | 
| 2 | green |  | 2 | two  |  | 2 | peter | 
| 3 | blue |  | 3 | one  |  +----+-------+ 
| 4 | yellow |  | 4 | three | 
+----+--------+  | 5 | six  | 
         | 6 | five | 
         +----+---------+ 

现在我想这个命令的结果：

+----+--------+ 
| id | colors | 
+----+--------+ 
| 1 | red | 
| 2 | ten | 
| 3 | jack | 
| 4 | green | 
| 5 | two | 
| 6 | peter | 
| 7 | blue | 
| 8 | one | 
| 9 | yellow | 
| 10 | three | 
| 11 | six | 
| 12 | five | 
+----+--------+ 

我该如何实现？ （应当指出，order by 1,2,3不为我工作）

Answer 1

这是你如何能做到这

select @rn:=@rn+1 as id,colors from (
    (select @rn1:= @rn1+1 as rn,colors from table1,(select @rn1:=0)x order by id) 
    union all 
    (select @rn2:= @rn2+1 as rn,numbers as colors from table2,(select @rn2:=0.5)x order by id) 
    union all 
    (select @rn3:= @rn3+1 as rn,names as colors from table3,(select @rn3:=0.6)x order by id) 
)x,(select @rn:=0)y order by rn ; 

的想法是为每个表项分配一个rn值，需要确保这些值总是按升序排列

所以，如果你运行的每个表的查询，你将有

mysql> select @rn1:= @rn1+1 as rn,colors from table1,(select @rn1:=0)x order by id; 
+------+--------+ 
| rn | colors | 
+------+--------+ 
| 1 | red | 
| 2 | green | 
| 3 | blue | 
| 4 | yellow | 
+------+--------+ 
4 rows in set (0.00 sec) 

mysql> select @rn2:= @rn2+1 as rn,numbers as colors from table2,(select @rn2:=0.5)x order by id; 
+------+--------+ 
| rn | colors | 
+------+--------+ 
| 1.5 | ten | 
| 2.5 | two | 
| 3.5 | one | 
| 4.5 | three | 
| 5.5 | six | 
| 6.5 | five | 
+------+--------+ 
6 rows in set (0.00 sec) 

mysql> select @rn3:= @rn3+1 as rn,names as colors from table3,(select @rn3:=0.6)x order by id; 
+------+--------+ 
| rn | colors | 
+------+--------+ 
| 1.6 | jack | 
| 2.6 | peter | 
+------+--------+ 
2 rows in set (0.00 sec) 

在这里你可以看到table1 rn个值1,2,3,.... table2值1.5,2.5,3.5,.... table3值1.6,2.6,....

所以最后当你所有的氡将它作为

1,1.5,1.6,2,2.5,2.6,....