Mysql Nested sub queries unknown column error

问题

i have a pretty big query with 2 sub queries. My big query updates an entire column E. The table looks like this:

--------------------------
id  | A      | B    | E  |
--------------------------
1   |  NULL  | NULL |NULL|
--------------------------
2   |  4     | 6    |NULL|
--------------------------
3   |  6     | 9    |NULL|
--------------------------

This is my entire query below:

 Update mydatabase.mytable  ,
    (SELECT t1.A/AVG(t2.A)
    FROM    mytable t1
    JOIN    mytable t2
    ON      t2.id <= t1.id
    group by t1.id ) AS C,
    (SELECT t1.B/AVG(t2.B)
    FROM    mytable t1
    JOIN    mytable t2
    ON      t2.id <= t1.id
    group by t1.id ) AS D
    SET E = (C+D)/2;

I get the error : Unknown column 'C' in 'field list'

believe i will also get the same error for D.

My subqueries work and the syntax is correct. i am just unsure of the big query and the update part.

Thanks,

EDIT: How can i edit the ON clause part of the query above such that i would like the current code to work where id<=14 (which is t2.id <= t1.id as shown above) so when t1 id =14, t2 is all the cumulative id from 1 to 14 as it is now.

but for id >14 I would like the ON clause to be (t2.id=t1.id>=t1.id-2 and <=t1.id) so when t1 id=15, t2.id should be between 13 and 15. when t1 id =16, t2.id should be between 14 and 16 and so on.

This is because when i calculate col E for ids after id=14, i am only interested in getting the average of the previous 2 rows for C and D on a moving average.

回答1:

You can rewrite your query using single join only no need to do additional join with conditions to calculate another value

Update t  join 
    (SELECT t1.A/AVG(t2.A) C ,t1.B/AVG(t2.B) D
    FROM    t t1
    JOIN    t t2
    ON      t2.id <= t1.id
    group by t1.id ) AS tt
    SET E = (tt.C + tt.D)/2;

Demo

Edit for null values

Update t  join 
    (SELECT t1.id ,ifnull(t1.A/AVG(t2.A),0) C ,ifnull(t1.B/AVG(t2.B),0) D
    FROM    t t1
    JOIN    t t2
    ON      t2.id <= t1.id
    group by t1.id ) AS tt
    on(t.id = tt.id)
    SET E = (tt.C + tt.D)/2;

Demo

来源：https://stackoverflow.com/questions/23776302/mysql-nested-sub-queries-unknown-column-error

标签

mysql

sql

subquery