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--- sql_analysis [2010/08/20 08:26] – daniel
+++ sql_analysis [2019/01/24 17:55] (current) – [Presence and count of specific mail headers] daniel
@@ Line 1: / Line 1: @@
- ====== Presence and count of certain headers ======
+ ====== Presence and count of specific mail headers ======
 This query extracts, for each of the header fields from a fixed list, the number of occurrences of all distinct values of the field.
@@ Line 8: / Line 8: @@
 FROM header, (values ('X-Priority'), ('Importance'), ('Precedence'), ('Priority'), ('X-MSMail-Priority'), ('X-MS-Priority')) as h(field)
 WHERE position(E'\n'||field IN lines)>0
-group by split_part(substr(lines, 1+position(E'\n'||field in lines), 200), E'\n', 1)
+group by 1
 </code>
+Sample output:
+<code>
+            ct             | count
+---------------------------+-------
+ Importance: high          |    32
+ Importance: High          |   130
+ Importance: low           |     1
+ Importance: Medium        |     3
+ Importance: normal        |    44
+ Importance: Normal        |   802
+ Precedence: bulk          | 19987
+ Precedence: bulk          |     1
+ Precedence: fm-user       |     3
+ Precedence: junk          |     3
+ Precedence: list          |  4026
+ Priority: non-urgent      |    11
+ Priority: Non-Urgent      |     1
+ Priority: normal          |   464
+ Priority: urgent          |   603
+ Priority: Urgent          |    12
+ X-MSMail-Priority: High   |   121
+ X-MSMail-Priority: Low    |     1
+ X-MSMail-Priority: Lowest |    11
+ X-MSMail-Priority: Medium |     3
+ X-MSMail-Priority: Middle |     8
+ X-MSMail-Priority: Normal |   923
+ X-Priority: 0             |     1
+ X-Priority: 1             |   102
+ X-Priority: 1 (High)      |     2
+ X-Priority: 1 (Highest)   |   120
+ X-Priority: 2             |     6
+ X-Priority: 2 (High)      |     1
+ X-Priority: 3             |  2892
+ X-Priority: 3 (Normal)    |   635
+ X-Priority: 5             |    14
+ X-Priority: Normal        |     5
+</code>
+This alternative implementation uses regular expressions and differs in that it doesn't limit header values to 200 characters or any other fixed length.
+<code sql>
+select FIELD||':'||arr[1], count(*)
+ from (select FIELD, regexp_matches(lines, '(?:^|\n)' || FIELD || ':\s*([^\n]*)', 'gi') as arr
+       from header,
+         (VALUES ('X-Priority'), ('Importance'), ('Precedence'), ('Priority'),
+             ('X-MSMail-Priority'), ('X-MS-Priority')) AS h(FIELD)
+             where strpos(lines,FIELD)>0) l
+GROUP BY 1 ORDER BY 1
+</code>
+In this version, the '' strpos(lines,FIELD)>0 '' condition is not essential: it's introduced only as a first-pass filter to eliminate the headers that don't contain anywhere any of the searched fields.
+====== Duplicate messages ======
+This query finds each message that share the exact same headers than another message with a lower mail_id, which means that it's a duplicate.
+<code sql>
+select h1.mail_id from header h1, header h2 where h1.lines=h2.lines and h1.mail_id > h2.mail_id
+</code>
+A stricter version, comparing the md5 hashes of bodies (text and html parts) in addition to the headers:
+<code sql>
+select b2.mail_id from body b1, body b2, header h1, header h2
+ where b1.mail_id < b2.mail_id
+ and h1.mail_id = b1.mail_id
+ and h2.mail_id = b2.mail_id
+ and md5(h1.lines) = md5(h2.lines)
+ and md5(b1.bodytext) is not distinct from md5(b2.bodytext)
+ and md5(b1.bodyhtml) is not distinct from md5(b2.bodyhtml);
+</code>
+The ''IS NOT DISTINCT'' comparator behaves as expected when ''bodytext'' or ''bodyhtml'' is NULL, as opposed
+to the simple equality operator, for which ''NULL=NULL'' is false
+====== Hierarchical view of tags  ======
+Output a list of tags sorted by hierarchy level and names,
+with an indentation to represent the hierarchy.
+<code sql>
+WITH RECURSIVE tagr(a,_tag_id,name,level) as (
+ select
+  array[row_number() over (order by name)] as a,
+  tag_id,
+  name,
+as level
+ from tags where parent_id is null
+UNION ALL
+ select
+   tagr.a || row_number() over (order by tags.name),
+   tag_id,
+   tags.name,
+   tagr.level+1
+ FROM tags JOIN tagr ON tagr._tag_id=tags.parent_id
+)
+select repeat('   ', level-1) || name from tagr order by a;
+</code>