nozzy

select
t1.*,
t2.sent_at
from message t1 
left join sent_log t2 on t2.message_id = t1.id
where t2.sent_at is null or t2.sent_at < here_datetime

триггер на DELETE в первой таблице, в триггере получаешь удаленный row и вставляешь в другую таблицу

Создай еще одно поле в таблице и пиши туда какие нужны id. А autoincrement не трогай, потом разберешься что это и для чего.

Что это за число 02 ?
Проверь что возвращает extract:

SELECT 
name, 
created_at,
extract(MONTH FROM created_at) 
FROM table 
WHERE name=0

select
t1.user_id,
sum(t1.amount),
count(*) as count
from your_table t1
inner join (
    select
    t2.user_id,
    t2.created_at
    from your_table t2
    where not exists (
        select 1 
        from your_table
        where user_id = t2.user_id
        and created_at < t2.created_at
    )
)   t3 on t3.user_id = t1.user_id 
    and t1.created_at between t3.created_at and t3.created_at + interval 5 day
group by t1.user_id
having(count <= 5)

Не проверял

update a t1
join b t2 on t2.id = t1.id_b
set t1.rate = 160
where t1.rate = 200
and t2.id_client = 2

SELECT
рынок,
SUM(объём_торгов),
TIMESTAMPADD(HOUR,TIMESTAMPDIFF(HOUR,CURDATE(),время),
    CURDATE()) AS round_date,
FROM your_table
GROUP BY рынок, round_date

pentaho report designer
community.pentaho.com/projects/reporting

select
t1.id,
t1.user_id,
t1.phone,
t1.date
from your_table t1
inner join 
(
  select 
  min(id) as min_id,
  user_id
  from your_table
  group by user_id
) t2 on t2.min_id = t1.id

select 
user_id,
date,
SUM(CASE WHEN currency = 'USD' THEN amount ELSE 0 END) AS USD,
SUM(CASE WHEN currency = 'EUR' THEN amount ELSE 0 END) AS EUR
FROM Table1 AS
GROUP BY user_id, date

или использовать IF:

SUM( IF(currency = 'USD', amount, 0) ) AS USD,
SUM( IF(currency = 'EUR', amount, 0) ) AS EUR

БД с веб-интерфейсом:
October CMS (на Laravel) или
Bolt CMS (попроще)

можно с union all:
SELECT COUNT(id) AS first_table_id, NULL AS second_table_id
FROM table1
WHERE model_id = 781
UNION ALL
SELECT NULL AS first_table_id, COUNT(id) AS second_table_id
FROM table2
WHERE model_id = 781

Писать в CSV файл.