Mysql使用另一个表中的值更新Null列，并重复该顺序

Question

I've a table named Series

 ID   NAME 
 1    generic  
 2    irregular  
 3    regular

Another table "Sections" which contains the column "series_id" and its currently NULL (for all rows).

 id title description series_id 1 Types produced Types of data produced NULL 2 Data standard Data and metadata standards NULL 3 Policies for access Policies for access and sharing NULL 4 Products of Research Products of Research NULL 5 Expected info Expected information NULL 6 Period of retention Period of data retention NULL 

I need to update the Sections table with id of Series table in a sequential order, and repeat the cycle till the end of Section rows. For example,

 id title description series_id 1 Types produced Types of data produced 1 2 Data standard Data and metadata standards 2 3 Policies for access Policies for access and sharing 3 4 Products of Research Products of Research 1 5 Expected info Expected information 2 6 Period of retention Period of data retention 3 

I came up with an initial query, but its setting the series_id as 1 for all rows. Also, I am unsure how to repeat the series_id for the remaining rows

UPDATE sections t1
JOIN   series t2
ON     t1.series_id = t2.id
SET    t1.series_id = t2.id
WHERE  t1.series_id IS NULL;

Any guidance is appreciated. Thanks in advance.

Answer 1

May be this might help:

SET @s =  MAX(id) From Series;
UPDATE sections t1
JOIN   series t2
ON     MOD(t1.id, @s) = MOD(t2.id, @s)
SET    t1.series_id = t2.id
WHERE  t1.series_id IS NULL;

Answer 2

You can't join both tables like that because there is no shared column. You can use a Unique Key with an extra column that has different values for all groups of 1,2,3 (eg A,B,C,D,E....) which will autoincrement series_id to 1,2,3. This might be the fastest solution. The extra column can be dropped after series_id is updated. Another way would be writing a procedure and using a loop.