SELECT sum(amount) AS 'Количество', 
(select CASE 
WHEN strftime('%w',dt)='0' THEN 'воскресенье' 
WHEN strftime('%w',dt)='1' THEN 'понедельник' 
WHEN strftime('%w',dt)='2' THEN 'вторник' 
WHEN strftime('%w',dt)='3' THEN 'среда' 
WHEN strftime('%w',dt)='4' THEN 'четверг' 
WHEN strftime('%w',dt)='5' THEN 'пятница' 
WHEN strftime('%w',dt)='6' THEN 'суббота' 
END) AS 'День недели' 
FROM tab1 GROUP BY strftime('%w',dt);

SELECT sum(amount) AS 'Количество', 
(select CASE strftime('%w',dt)
WHEN '0' THEN 'воскресенье' 
WHEN '1' THEN 'понедельник' 
WHEN '2' THEN 'вторник' 
WHEN '3' THEN 'среда' 
WHEN '4' THEN 'четверг' 
WHEN '5' THEN 'пятница' 
WHEN '6' THEN 'суббота' 
END) AS 'День недели' 
FROM tab1 GROUP BY strftime('%w',dt);

SELECT tab1.name, (SELECT CASE tab1.id WHEN 1 THEN 1 ELSE 1 END) AS idd , sum(tab2.amount) FROM tab1, tab2 WHERE idd = tab2.idTab1 GROUP BY 1;

SELECT tab1.name, (SELECT CASE WHEN  tab1.id >2 THEN tab1.id-1  END) AS idd , sum(tab2.amount) FROM tab1, tab2 WHERE idd = tab2.idTab1 GROUP BY 1;

SELECT tab1.name, sum(tab2.amount) FROM tab1, tab2 WHERE (SELECT CASE WHEN  tab1.id >2 THEN tab1.id-1  END)  = tab2.idTab1 GROUP BY 1;