Question

我想使用COUNT结果作为ORACLE上的IF CONDITION，就像oracle上的伪代码一样：

select count(d.number_people) as counted_people
from dual d
if counted_people = 1 then
dbms_output.put_line('Have just one people on this column.'
end if;

这种语法是错误的，我知道，我该如何正确使用它？

Answer 1

使用SELECT ... INTO variable ...

演示：https://dbfiddle.uk/?rdbms=oracle_11.2&fiddle=610d02797857539be5fcd4afdbd7d9e6

DECLARE 
  cnt number;
BEGIN
  select count(*) INTO cnt from dual;
  IF cnt = 1 THEN
     DBMS_OUTPUT.PUT_LINE('Exaclty one record');
  ELSE
     DBMS_OUTPUT.PUT_LINE('0 or more than 1  record');
  END IF;
END;
/

Answer 2

COUNT是聚合结果。您可以计算表中的所有行，符合特定条件的所有行等。作为汇总结果，可以在SELECT子句，HAVING子句和{{ 1}}子句。（您不能在ORDER BY子句中使用它，因为WHERE子句处理表行中的数据。您需要一个WHERE子句来处理聚合结果。） / p>

SELECT子句/ ORDER BY子句示例

HAVING

HAVING子句示例

select
  supplier_id,
  case when count(*) < 20 then 'less then 20 orders'
       when count(*) < 40 then 'less beteen 20 and 40 orders'
       else '40 or more orders'
  end as number_of_orders
from orders
where order_date >= date '2018-01-01'
group by supplier_id
order by count(*) desc;

如何在ORACLE上将计数作为IF条件传递

2 个答案: