是否可以使用 sql%rowcount 进行 SELECT？

Question

下面的代码可能返回不止一行。 sql%rowcount 会返回获取的行数吗？

select * from emp where empname = 'Justin' and dept='IT'
if sql%rowcount>0
    ...

这是我的示例过程；我是否以正确的方式使用sql%rowcount？

CREATE PROCEDURE Procn(in_Hid IN VARCHAR2,outInststatus OUT VARCHAR2,outSockid IN NUMBER,outport OUT VARCHAR2,outIP OUT VARCHAR2,outretvalue OUT NUMBER)
AS
BEGIN
select INST_STATUS into outInststatus from TINST_child where INST_ID = in_Hid and INST_STATUS = 'Y';
if outInststatus = 'Y' then 
     select PORT_NUMBER,STATIC_IP into outport,outIP from TINST where INST_ID = in_Hid and IP_PORT_STATUS = 'Y';
    if sql%rowcount >= 1 then
       select SOCK_ID into outSockid from TINST where PORT_NUMBER = outport AND STATIC_IP = outIP;  
       outretvalue := 0;
    else
       outretvalue := -12;
    end if;
  EXCEPTION
  WHEN NO_DATA_FOUND THEN
   outretvalue := -13;
end if;
END;

Answer 1

是的，您可以使用SQL%ROWCOUNT。在 PL/SQL 中有效。

但是，在 PL/SQL 中，您的查询结果需要发送到某个地方，例如到 PL/SQL 表中。 PL/SQL 永远不会将结果发送到输出（终端、窗口等）。所以SELECT * FROM 不起作用。

您的代码可能如下所示：

DECLARE
  TYPE emp_t ...;
  emp_tab emp_t;

BEGIN
  SELECT *
  BULK COLLECT INTO emp_tab
  FROM emp
  WHERE empname = 'Justin' AND dept='IT';

  IF sql%rowcount > 0 THEN
    .. do something ...
  END IF;
END;
/

更新：

更新后的问题表明您正在寻找其他东西。

选项 1：使用例外

如果有 0 行或多于 1 行，这些情况分别处理（作为错误）：

BEGIN
  select PORT_NUMBER,STATIC_IP into outport, outIP
  from TINST
  where INST_ID = in_Hid AND IP_PORT_STATUS = 'Y';

EXCEPTION
  WHEN NO_DATA_FOUND THEN
    outretvalue := -12;
    RETURN;

  WHEN TOO_MANY_ROWS THEN
    outretvalue := -13;
    RETURN;
END;

选项 2：使用聚合

使用聚合，查询将始终只返回一行。如果现在源行与 WHERE 子句匹配，则两个结果值都将为 NULL。如果 WHERE 子句匹配多于一行，则取最大值。

请注意，此查询可能会返回最初不在同一行的端口号和 IP 地址。

select MAX(PORT_NUMBER), MAX(STATIC_IP) into outport, outIP
from TINST
where INST_ID = in_Hid AND IP_PORT_STATUS = 'Y';

IF outport IS NULL OR outIP IS NULL THEN
    outretvalue := -12;
    RETURN;
END IF;

选项 3：使用 ROWNUM

此查询最多返回一行。如果没有行匹配 WHERE 子句，则抛出异常并需要处理：

BEGIN
  select PORT_NUMBER, STATIC_IP into outport, outIP
  from TINST
  where INST_ID = in_Hid AND IP_PORT_STATUS = 'Y'
  AND ROWNUM = 1;

EXCEPTION
  WHEN NO_DATA_FOUND THEN
    outretvalue := -12;
    RETURN;

END;

Answer 2

根据您的评论

如果第二个“选择”查询返回不止一行，我想取第一行并处理它

...这应该可以工作，但可能并不像您期望的那样，因为您尚未定义“第一个”的含义。

CREATE PROCEDURE Procn(in_Hid IN VARCHAR2, outInststatus OUT VARCHAR2,
    outSockid IN NUMBER, outport OUT VARCHAR2, outIP OUT VARCHAR2,
    outretvalue OUT NUMBER)
AS
BEGIN
    select INST_STATUS into outInststatus
    from TINST_child
    where INST_ID = in_Hid and INST_STATUS = 'Y';

    -- no need to check if outInstatus is Y, that's all it can be here

    -- restricting with `rownum` means you'll get at most one row, so you will
    -- not get too_many_rows. But it will be an arbitrary row - you have no
    -- criteria to determine which of the multiple rows you want. And you can
    -- still get no_data_found which will go to the same exception and set -12
    select PORT_NUMBER, STATIC_IP into outport, outIP
    from TINST
    where INST_ID = in_Hid and IP_PORT_STATUS = 'Y'
    and rownum < 2;

    -- no need to check sql%rowcount; it can only be 1 here

    -- not clear if this can return multiple rows too, and what should happen
    -- if it can; could use rownum restriction but with the same caveats
    select SOCK_ID into outSockid
    from TINST
    where PORT_NUMBER = outport AND STATIC_IP = outIP;   

    outretvalue := 0;
EXCEPTION
    WHEN NO_DATA_FOUND THEN
        outretvalue := -12;
END;

---

exception 处理程序适用于整个block。如果任何select 语句没有找到任何行，则该块将处理no_data_found 异常并将outretvalue 设置为-12。

如果您想为每个 select 使用不同的 outretvalue，那么您可以将它们包装在子块中，每个子块都有自己的异常处理部分：

CREATE PROCEDURE Procn(in_Hid IN VARCHAR2, outInststatus OUT VARCHAR2,
    outSockid IN NUMBER, outport OUT VARCHAR2, outIP OUT VARCHAR2,
    outretvalue OUT NUMBER)
AS
BEGIN
    BEGIN
        select INST_STATUS into outInststatus
        from TINST_child
        where INST_ID = in_Hid and INST_STATUS = 'Y';
    EXCEPTION
        WHEN NO_DATA_FOUND THEN
            outretvalue := -12;
    END;

    BEGIN
        select PORT_NUMBER, STATIC_IP into outport, outIP
        from TINST
        where INST_ID = in_Hid and IP_PORT_STATUS = 'Y'
        and rownum < 2;
    EXCEPTION
        WHEN NO_DATA_FOUND THEN
            outretvalue := -13;
    END;

    BEGIN
        select SOCK_ID into outSockid
        from TINST
        where PORT_NUMBER = outport AND STATIC_IP = outIP;   
    EXCEPTION
        WHEN NO_DATA_FOUND THEN
            outretvalue := -14;
    END;

    outretvalue := 0;
END;

如果调用者需要知道哪个select 失败了，并且如果你从未真正期望它们中的任何一个失败，那么你只需要这样做，那么可能更常见的是根本不捕获异常并让调用者看到原始no_data_found 并决定要做什么。不过，这取决于异常条件对您和您的应用程序意味着什么。