I have three tables organized as depicted below, showing foreign keys and unique fields (green):

Simplified tables

That represents email messages received by a server. (Sorry I couldn't simplify more. Full version here.) Each message is authenticated according to SPF and DKIM, and thereby linked to the corresponding domains. An SPF authentication can be linked to two domains, the so-called helo domain, which is the name of the sending server, and the bounce address domain, which usually is the domain-part (the part after the at-sign) of the author's email address. DKIM, instead, permits any domain through which the message passed to add one or more signatures, in order to claim some responsibility for the message itself. Usually, a message carries one or two DKIM signatures, but there can be more of them.

The many-to-many msg_ref table is created as follows (see db<>fiddle for tables creation and example data):

CREATE TABLE msg_ref (
  message_in INT UNSIGNED NOT NULL COMMENT 'Foreign key to message_in',
  domain INT UNSIGNED NOT NULL COMMENT 'Foreign key to domain',
  auth SET ('author', 'spf_helo', 'spf', 'dkim', 'org', 'dmarc') NOT NULL,
  spf ENUM ('none', 'neutral', 'pass', 'fail', 'softfail', 'temperror', 'permerror') NOT NULL,
  dkim ENUM ('none', 'pass', 'fail', 'policy', 'neutral', 'temperror', 'permerror') NOT NULL,
  INDEX by_dom_msg(domain, message_in),
  INDEX by_msg_auth(message_in, auth)

In order to provide feedback about authentication, DMARC introduced aggregate reports to be sent at end-of-day to the domains who request them. A report communicates to the sender the results of authentication checks carried out by the receiver. It consists of various rows containing the source IP of the last relay (from message_in, converted), the number of messages having the same authentication results, and the results proper (from msg_ref).

Here's a query to extract an SPF and up to four DKIM results:

SELECT INET_NTOA(CONV(HEX(m.ip),16,10)) AS source, COUNT(DISTINCT(m.id)) AS count,\
m.dmarc_dispo AS disposition, \
da.domain AS author,\
dspf.domain AS spf, rspf.spf AS spf_result,\
d1.domain AS dkim1, r1.dkim AS dkim1_result,\
d2.domain AS dkim2, r2.dkim AS dkim2_result,\
d3.domain AS dkim3, r3.dkim AS dkim3_result,\
d4.domain AS dkim4, r4.dkim AS dkim4_result\
FROM message_in AS m\
LEFT JOIN (msg_ref AS rd INNER JOIN domain AS dd ON rd.domain = dd.id)\
  ON m.id = rd.message_in AND FIND_IN_SET('dmarc', rd.auth)\
LEFT JOIN (msg_ref AS ra INNER JOIN domain AS da ON ra.domain = da.id)\
  ON m.id = ra.message_in AND FIND_IN_SET('author', ra.auth)\
LEFT JOIN (msg_ref AS rspf INNER JOIN domain AS dspf ON rspf.domain = dspf.id)\
  ON m.id = rspf.message_in AND FIND_IN_SET('spf', rspf.auth)\
LEFT JOIN (msg_ref AS rhelo INNER JOIN domain AS dhelo ON rhelo.domain = dhelo.id)\
  ON m.id = rhelo.message_in AND FIND_IN_SET('spf_helo', rhelo.auth)\
LEFT JOIN (msg_ref AS r1 INNER JOIN domain AS d1 ON r1.domain = d1.id)\
  ON m.id = r1.message_in AND r1.dkim_order = 1\
LEFT JOIN (msg_ref AS r2 INNER JOIN domain AS d2 ON r2.domain = d2.id)\
  ON m.id = r2.message_in  AND r2.dkim_order = 2\
LEFT JOIN (msg_ref AS r3 INNER JOIN domain AS d3 ON r3.domain = d3.id)\
  ON m.id = r3.message_in AND r3.dkim_order = 3\
LEFT JOIN (msg_ref AS r4 INNER JOIN domain AS d4 ON r4.domain = d4.id)\
  ON m.id = r4.message_in  AND r4.dkim_order = 4\
GROUP BY source, disposition, author,\
 spf, spf_result,\
 dkim1, dkim1_result,\
 dkim2, dkim2_result,\
 dkim3, dkim3_result,\
 dkim4, dkim4_result

Not shown, there is a WHERE clause that limits the output to a specific rd.domain and an m.mtime lying within the given reporting period. The result is the content of the DMARC report, as described by wikipedia:

| source    | count | disposition | Header from | spf         | spf_result | dkim1       | dkim1_result | dkim2       | dkim2_result | dkim3       | dkim3_result | dkim4       | dkim4_result |
| |    12 | none        | example.com | example.com | pass       | example.com | pass         | example.com | pass         | example.net | pass         | example.net | pass         |
| |     1 | none        | example.com | example.com | pass       | example.com | pass         | example.net | pass         | example.net | pass         | NULL        | NULL         |
2 rows in set (0.004 sec)

Edited Questions:

(Removed non-working attempt and possibly ambiguous wording. Reordered most important first.)

  • How to express the query using Recursive CTE so that the resulting rows contain a variable number of dkim<n> and dkim<n>_result columns, covering all DKIM authentications that appear in the relevant messages.

  • How to significantly simplify the query by factoring repeated expressions.

Note: The query is filtered through OpenDBX. It can use several DBMS, MariaDB v.15 is a reasonable target.

  • 2
    1) Your CTE is NOT recursive. 2) Your problem is absolutely unclear. A lot of words and little meaning. Provide: CREATE TABLE for all tables (including FKs!!); INSERT INTO with some sample data; desired output for this data with detailed explanations which refers to definite values. Or you may create a fiddle instead of scripts (for exampe, on dbfiddle.uk).
    – Akina
    Apr 6, 2021 at 19:01
  • Hi, and welcome to the forum! Your question is very complex - I don't have a running instance of MySQL, but do you have the source of odbx_example.sql? I would give serious consideration to removing the ENUMs and SETs - use lookup tables instead! What happens in your query if you use UNION ALL instead of UNION? Have something like x = 1..... r1.dkim_order = x... UNION ALL x = x + 1... r2.dkim_order = x WHERE x < 20 Look here.
    – Vérace
    Apr 6, 2021 at 19:19
  • I defined the query on dbfiddle.uk, using repeated dkim=1, 2, 3, 4. That way reporting is incomplete whenever there are more than 4 dkim signatures in a message.
    – Ale
    Apr 7, 2021 at 17:08
  • I'm not clear why my attempt is not recursive.
    – Ale
    Apr 8, 2021 at 7:23
  • Here's the source for odbx_example.sql. The query is configurable, and so stays in odbx_example.conf.
    – Ale
    Apr 8, 2021 at 7:29

1 Answer 1


Like most (all?) SQL queries the number of columns in the result is fixed. Recursive CTEs can only add rows and not columns.

You are fortunate that the result you want to generate a ARF report is a XML. Because of this you can use good old GROUP_CONCAT to generate an XML form of the DKIM.

I haven't looked up the XML spec for the report however something in the form

  ) ORDER BY r1.dkim_order SEPARATOR '') dkim_result
FROM message_in AS m

Other recommendations:

  • Use InnoDB as the table type and not MyISAM/Aria
  • If MariaDB-10.5 is the sole application use the INET6 datatype introduced in 10.5
  • DKIM enums are probably ok as defined in spec and the DKIM working group of the IETF is "Concluded WG". So nothing more is coming.
  • For non-dkim - probably separate tables of message_id, auth domain columns for each time. Then just join to those as required.

ref: fiddle

  • Thank you very much for your answer. I didn't know about GROUP_CONCAT(). However, it lacks the ability to use COUNT(*), "Invalid use of group function". Also, I cannot add the resulting column to the SELECT's GROUP BY clause. I can add it to the result anyway, as a sort of check point. In this fiddle it would let me realize there was one more signature than I queried for, but without bringing additional knowledge. Must use DISTINCT, otherwise it returns an inordinate amount of data for just 15 msg.
    – Ale
    Apr 12, 2021 at 9:48
  • DISTINCT is hiding problems. As you want to sum the aggregated results, it needs to be a subquery. Bottom query in fiddle. spf should be in your messages_in table as there's only one SPF result per message. As you can see its inflating the count.
    – danblack
    Apr 13, 2021 at 1:27
  • 1
    Great! Moving GROUP_CONCAT inside a subquery allows to group by that column. That way, the number of matching messages, COUNT(DISTINCT(m.id)) (see fiddle), agrees with the result of the original query. I'll have to reintroduce the fields I simplified out and sort dkim_order "by hand" (ORDER BY doesn't seem to be observed), but now I have a query which does not depend on a max number of DKIM signatures. In addition, it looks much simpler. Thanks a lot!!
    – Ale
    Apr 13, 2021 at 10:00
  • GROUP_CONCAT(DISTINCT .. ORDER BY .. ) is a known bug. However you don't need DISTINCT in the GROUP BY as there only one set of domain information per message. I do, finally see the case for it in COUNT(DISTINCT...)
    – danblack
    Apr 14, 2021 at 2:42

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