oracle 存储过程 读取顺序错误

调用下面存储过程 出现 读取顺序错误的 提示，
大家帮忙看下 谢谢～～！


PROCEDURE RetrieveNonblockingInstanceIds
(
p_OWNER_ID IN INSTANCE_STATE.OWNER_ID%TYPE := NULL
,p_OWNED_UNTIL IN INSTANCE_STATE.OWNED_UNTIL%TYPE := NULL
,p_NOW IN DATE
,p_WORKFLOW_IDS OUT RefCursor
)
AS
BEGIN
OPEN p_WORKFLOW_IDS FOR
SELECT
INSTANCE_ID
from
INSTANCE_STATE
WHERE
BLOCKED = 0
AND STATUS NOT IN (c_STATUS_COMPLETED, c_STATUS_SUSPENDED, c_STATUS_TERMINATED)
AND (OWNER_ID IS NULL OR OWNED_UNTIL < p_NOW)
FOR UPDATE;

IF NVL(SQL%ROWCOUNT, 0) > 0
THEN
UPDATE INSTANCE_STATE
SET
OWNER_ID = p_OWNER_ID
,OWNED_UNTIL = p_OWNED_UNTIL
WHERE
BLOCKED = 0
AND STATUS NOT IN (c_STATUS_COMPLETED, c_STATUS_SUSPENDED, c_STATUS_TERMINATED)
AND (OWNER_ID IS NULL OR OWNED_UNTIL < p_NOW);
END IF;
END;

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详细错误提示？

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ORA-01002: 读取违反顺序

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应该使用sys_refcursor

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弱弱的提个疑问：
假如for update这里锁了3条，在if的时候，有别的会话插了一条刚好满足条件，则下面的更新会不会有4条啊。

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Cause In a host language program, a FETCH call was issued out of sequence. A successful parse-and-execute call must be issued before a fetch. This can occur if an atte