查詢

Question

，我會解決這個查詢

Display id, dates and time of all "LASER" interventions involving only doctors Having less than 30 years.

，但我有一個錯誤：

select i.id, i.data_e_ora

from persona p join medico m

on p.cf=m.cf

join effettua e

on m.cf=e.cf_med

join intervento i

on e.id_int=i.id

where i.tipo='LASER' and p.data_nascita=((sysdate-p.data_nascita)/365)<30

ERROR at line 9: 
ORA-00932: inconsistent datatypes: expected DATE got NUMBER 

表：

CF          NOT NULL CHAR(16) 
NOME            VARCHAR2(30) 
COGNOME           VARCHAR2(30) 
DATA_NASCITA          DATE 
SESSO            CHAR(1) 

Answer 1

你只需要修復where條款。這是過於雄心勃勃：

select i.id, i.data_e_ora 
from persona p join 
    medico m 
    on p.cf = m.cf join 
    effettua e 
    on m.cf = e.cf_med join 
    intervento i 
    on e.id_int = i.id 
where i.tipo = 'LASER' and 
     p.data_nascita > (sysdate - 365.25 * 30); 

注：扣除年的一個更好的方法是實際減去年：

where p.data_nascita > sysdate - interval '30' year