Here is your original query from the question
SELECT e.*, MAX(m.datetime) AS unread_last, COUNT(m.id) AS unread
FROM TAB_EVENT e
LEFT JOIN TAB_MESSAGE m ON e.id=m.event_id
WHERE ( m.`read` IS NULL OR m.`read` = 0)
GROUP BY e.id
ORDER BY m.datetime DESC, e.id ASC
LIMIT 10;
Maybe try refactoring the query in such a way that in executes in this sequence
- only collect necessary columns from TAB_MESSAGE
- apply LIMIT 10 against the collected rows from TAB_MESSAGE
- run the JOIN
- apply the MAX() and COUNT() last
Here is what I am proposing
SELECT e.*, MAX(m.datetime) AS unread_last, COUNT(m.id) AS unread
FROM
(
SELECT * FROM
(SELECT id,event_id,datetime FROM TAB_MESSAGE
WHERE read IS NULL OR read = 0
ORDER BY datetime DESC) mm
LIMIT 10
) m
LEFT JOIN TAB_EVENT e
ON e.id=m.event_id
ORDER BY m.datetime DESC, e.id ASC;
Give it a Try !!!
UPDATE 2012-02-21 17:06 EDT
SELECT e.*, MAX(m.datetime) AS unread_last, COUNT(m.id) AS unread
FROM
TAB_EVENT e LEFT JOIN
(
SELECT * FROM
(SELECT id,event_id,datetime FROM TAB_MESSAGE
WHERE read IS NULL OR read = 0
ORDER BY datetime DESC) mm
LIMIT 10
) m
ON e.id=m.event_id
ORDER BY m.datetime DESC, e.id ASC;
@Sebastian, I put the query back in the original join order. Please try this as well !!!
UPDATE 2012-02-21 17:11 EDT
Make sure the datetime field is indexed
ALTER TABLE TAB_MESSAGE ADD INDEX read_datetime_ndx (read,datetime);
Your last query
mysql> select table_name from tables as a left join (select distinct table_name from tables as b) on a.table_name!=b.table_name;
ERROR 1248 (42000): Every derived table must have its own alias
fails because the as b must be outside the parentheses like this
mysql> select table_name from tables as a left join (select distinct table_name from tables) as b on a.table_name!=b.table_name;
Your method 2 failed
mysql> select count(table_name) as num, table_name from tables group by table_name where num > 1;
because the group by table_name must be last like this
mysql> select count(table_name) as num, table_name from tables where num > 1 group by table_name;
SUGGESTION
Perhaps you should start with a GROUP BY ... HAVING query like this
SELECT table_name,COUNT(1) table_count
FROM information_schema.tables
WHERE table_schema NOT IN
('information_schema','performance_schema','mysql')
GROUP BY table_name HAVING COUNT(1) > 1;
This will definitely give all tables whose name appears in multiple databases
Form that as a subquery and join it to gather all databases the table appears in
SELECT
A.table_name,
GROUP_CONCAT(B.table_schema) TheTableAppearsInTheseDatabases
FROM
(
SELECT table_name,COUNT(1) table_count
FROM information_schema.tables
WHERE table_schema NOT IN
('information_schema','performance_schema','mysql')
GROUP BY table_name HAVING COUNT(1) > 1
) A INNER JOIN information_schema.tables B
USING (table_name) GROUP BY A.table_name;
Please notice that I use INNER JOIN rather than LEFT JOIN because it will really form a Cartesian product (2704 X 2704) and then perform comparisons.
I know this works because I tried it out in MySQL 5.5.12 on my Windows7 machine
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 33
Server version: 5.5.12-log MySQL Community Server (GPL)
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Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> SELECT
-> A.table_name,
-> GROUP_CONCAT(B.table_schema) TheTableAppearsInTheseDatabases
-> FROM
-> (
-> SELECT table_name,COUNT(1) table_count
-> FROM information_schema.tables
-> WHERE table_schema NOT IN
-> ('information_schema','performance_schema','mysql')
-> GROUP BY table_name HAVING COUNT(1) > 1
-> ) A INNER JOIN information_schema.tables B
-> USING (table_name) GROUP BY A.table_name;
+--------------------------+-------------------------------------------------------------------------------------------------------------------+
| table_name | TheTableAppearsInTheseDatabases |
+--------------------------+-------------------------------------------------------------------------------------------------------------------+
| a | junk,test,robottinosino |
| acl | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive |
| blocks | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| blog | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive |
| blog_category | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| blog_entrycat | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive |
| blog_meta | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_archive,weisci_jaws_staging2 |
| blog_trackback | weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging |
| calendar_events | weisci_jaws_staging,weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2 |
| calendar_meta | weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging |
| calendar_questions | weisci_jaws_staging,weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2 |
| calendar_tickets | weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging |
| calendar_transactions | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging,weisci_jaws_archive |
| captcha_complex | weisci_jaws_staging,weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2 |
| change_log | test,junk |
| chat_staff | test,junk |
| comments | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging,weisci_jaws_archive |
| donations_charities | weisci_jaws_staging,weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2 |
| donations_charities_meta | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| donations_donations | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| foo_reference1 | timpost1,timpost2 |
| foo_reference2 | timpost1,timpost2 |
| foo_reference3 | timpost1,timpost2 |
| groups | weisci_jaws_staging,weisci_jaws_archive,weisci_jaws_live,weisci_jaws_staging2 |
| ipvisitor | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| job_post | giannosfor,test |
| layout | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| listeners | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| mediamanager_files | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_staging |
| mediamanager_group | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| mediamanager_photos | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| mediamanager_video | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| menus | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| menus_groups | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| mytable | ryanzec,user1267617,cabita,dotancohen,johnlocke,neeraj,test,user391986,cool_cs,javier,mathieu |
| mytext | jakobud,newstuff |
| occupation_field | giannosfor,test |
| policy_agentblock | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| policy_ipblock | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| prova | veto,vito |
| registry | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| registry_bk | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| session | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| static_pages | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| static_pages_translation | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| t | preeti,rollup_test |
| t1 | abidibo,test |
| t2 | test,abidibo |
| t3 | test,abidibo |
| table1 | table_test,supercoolville,test |
| table2 | supercoolville,test,table_test |
| tags | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| tags_content | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| tbl_banner_position | weisci_jaws_staging2,weisci_jaws_live |
| tbl_banner_upload | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| tbl_global_banner | weisci_jaws_staging2,weisci_jaws_live |
| tms_authors | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| tms_repositories | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| tms_themes | weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging |
| updates | test,junk |
| url_aliases | weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2,weisci_jaws_archive |
| url_maps | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| users | weisci_jaws_archive,weisci_jaws_staging,giannosfor,veto,weisci_jaws_live,weisci_jaws_staging2,friends,sample,vito |
| users_groups | weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live,weisci_jaws_staging2 |
| users_meta | weisci_jaws_staging2,weisci_jaws_archive,weisci_jaws_staging,weisci_jaws_live |
+--------------------------+-------------------------------------------------------------------------------------------------------------------+
65 rows in set (0.91 sec)
mysql>
Give it a Try !!!
Best Answer
http://searchoracle.techtarget.com/answer/Sum-of-two-table-row-counts-as-one-answer
Finally I've found it at given link