SQL

Question

我正在尝试使用 for 循环从游标循环遍历存储过程中的结果。该循环在以下示例中正确运行：

CREATE OR REPLACE PROCEDURE ML_ANOMALY_EVENT_CREATOR ()
    DYNAMIC RESULT SETS 1
P1: BEGIN

    DECLARE DATETIME_TEMP TIMESTAMP(6);
    DECLARE TAG_GROUP_TEMP VARCHAR(50);
    DECLARE EVENT_CODE VARCHAR(100);
    DECLARE STMT VARCHAR(1000);
    SET STMT = 'INSERT INTO ML_ANOMALY_EVENTS VALUES(?, ?, CURRENT TIMESTAMP, ?, CURRENT TIMESTAMP)';
    PREPARE S1 FROM STMT;

    FOR v AS AD_DATA CURSOR FOR (SELECT DATETIME, TAG_GROUP FROM ML_AD_MV WHERE DATETIME > (SELECT MAX(DATETIME_END) FROM ML_ANOMALY_EVENTS) AND ANOMALY=2 ORDER BY 2, 1)
        DO
            SET DATETIME_TEMP = v.DATETIME;
            SET TAG_GROUP_TEMP = v.TAG_GROUP;
            SET EVENT_CODE = 'TEST';
            EXECUTE S1 USING EVENT_CODE, TAG_GROUP_TEMP, DATETIME_TEMP;
    END FOR;

END P1

当我在下面尝试这个时，它失败了。我想在我声明的变量的帮助下从某个 table 中提取结果，并且如果结果包含任何行，则只做一些事情（在这个例子中是插入）：

CREATE OR REPLACE PROCEDURE ML_ANOMALY_EVENT_CREATOR ()
    DYNAMIC RESULT SETS 1
P1: BEGIN

    DECLARE DATETIME_TEMP TIMESTAMP(6);
    DECLARE TAG_GROUP_TEMP VARCHAR(50);
    DECLARE EVENT_CODE VARCHAR(100);
    DECLARE STMT VARCHAR(1000);
    SET STMT = 'INSERT INTO ML_ANOMALY_EVENTS VALUES(?, ?, CURRENT TIMESTAMP, ?, CURRENT TIMESTAMP)';
    PREPARE S1 FROM STMT;

    FOR v AS AD_DATA CURSOR FOR (SELECT DATETIME, TAG_GROUP FROM ML_AD_MV WHERE DATETIME > (SELECT MAX(DATETIME_END) FROM ML_ANOMALY_EVENTS) AND ANOMALY=2 ORDER BY 2, 1)
        DO
            SET DATETIME_TEMP = v.DATETIME;
            SET TAG_GROUP_TEMP = v.TAG_GROUP;
            SET EVENT_CODE = 'TEST';
            --EXECUTE S1 USING EVENT_CODE, TAG_GROUP_TEMP, DATETIME_TEMP;

            DECLARE EVENT_CHECKER CURSOR FOR
                SELECT * FROM ML_ANOMALY_EVENTS WHERE TAG_GROUP=TAG_GROUP_TEMP AND DATETIME >= DATETIME_TEMP;

            OPEN EVENT_CHECKER;
                IF (EVENT_CHECKER IS FOUND) THEN
                    EXECUTE S1 USING EVENT_CODE, TAG_GROUP_TEMP, DATETIME_TEMP;
                END IF;
            CLOSE EVENT_CHECKER;

    END FOR;

END P1

我该如何解决这个问题？

Answer 1

不需要 event_checker 光标。尝试

if ((SELECT count(*) FROM ML_ANOMALY_EVENTS 
     WHERE TAG_GROUP=TAG_GROUP_TEMP AND DATETIME >= DATETIME_TEMP ) > 0) then
   EXECUTE S1 USING EVENT_CODE, TAG_GROUP_TEMP,DATETIME_TEMP;
end if

Answer 2

虽然 Wen-Yi Chua 的回答有效，但这里使用 EXISTS 谓词代替聚合更有效：

IF EXIST (SELECT 1 FROM ML_ANOMALY_EVENTS 
          WHERE TAG_GROUP=TAG_GROUP_TEMP AND DATETIME >= DATETIME_TEMP) THEN ...

尤其是当您希望条件在大多数情况下为真时。 EXISTS 将在找到与搜索条件匹配的单个记录后立即 return，而带有 COUNT(*) 的查询将必须读取所有匹配的记录。

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