我有一个存储过程，我在游标中循环结果。我遇到的问题是license_attributes值在它不应该是的时候始终为null。如果我在存储过程之外执行select语句，或者作为调试在存储过程中执行游标外的select语句，我得到的结果是我期待的（非空）
这是select中始终在游标中返回null的部分：
(SELECT
CONCAT('{""',sf.Asset_Attribute__c.Type__c,'"": {',GROUP_CONCAT(
'""',sf.Asset_Attribute__c.Key__c,'"":""',LOWER(sf.Asset_Attribute__c.Value__c),'""'
),'}}')
FROM
sf.Asset_Attribute__c
WHERE
sf.Asset_Attribute__c.Asset__c = license_id
GROUP BY sf.Asset_Attribute__c.Asset__c) AS `license_attributes`
以下是存储过程的部分：
GETCLOUDACCOUNTS:BEGIN
DECLARE no_more_cloud_accounts_records boolean DEFAULT FALSE;
DECLARE company VARCHAR(255) DEFAULT null;
DECLARE license_status VARCHAR(50) DEFAULT null;
DECLARE license_id VARCHAR(18) DEFAULT null;
DECLARE cloud_owner_email VARCHAR(255) DEFAULT null;
DECLARE entitlement_plan VARCHAR(255) DEFAULT null;
DECLARE role VARCHAR(500) DEFAULT null;
DECLARE is_trial BOOLEAN DEFAULT false;
DECLARE license_attributes VARCHAR(2000) DEFAULT null;
DECLARE zuora_account_id VARCHAR(100) DEFAULT '';
DECLARE zuora_account_number VARCHAR(50) DEFAULT null;
DECLARE zuora_account_status VARCHAR(50) DEFAULT null;
DECLARE zuora_account_last_invoice_date DATETIME DEFAULT null;
DECLARE has_active_subscriptions BOOLEAN DEFAULT false;
DECLARE cloud_accounts_cursor CURSOR FOR
SELECT
(SELECT `sf`.`Contact`.`CompanyName__c` FROM `sf`.`Contact` WHERE `sf`.`Asset`.`ContactId`=`sf`.`Contact`.`Id`) AS `company`,
`sf`.`License_Key_Association__c`.`License_Key_Status__c` AS `license_status`,
`sf`.`License_Key_Association__c`.`License_Key__c` AS `license_id`,
`sf`.`Asset`.`ContactEmail__c` AS `cloud_owner_email`,
(SELECT `sf`.`Contact`.`CloudEntitlementPlan__c` FROM `sf`.`Contact` WHERE `sf`.`Asset`.`ContactId`=`sf`.`Contact`.`Id`) AS `entitlement_plan`,
`sf`.`License_Key_Association__c`.`Role__c` AS `role`,
IF( (SELECT `sf`.`Product2`.`IsCommercial__c` FROM `sf`.`Product2` WHERE `sf`.`Product2`.`Id`=`sf`.`Asset`.`Product2Id`) = 0,true,false ) AS `is_trial`,
(SELECT
CONCAT('{""',sf.Asset_Attribute__c.Type__c,'"": {',GROUP_CONCAT(
'""',sf.Asset_Attribute__c.Key__c,'"":""',LOWER(sf.Asset_Attribute__c.Value__c),'""'
),'}}')
FROM
sf.Asset_Attribute__c
WHERE
sf.Asset_Attribute__c.Asset__c = license_id
GROUP BY sf.Asset_Attribute__c.Asset__c) AS `license_attributes`
FROM
`sf`.`License_Key_Association__c`
LEFT JOIN `sf`.`Asset`
ON `sf`.`License_Key_Association__c`.`License_Key__c` = `sf`.`Asset`.`Id`
JOIN `sf`.`Contact`
ON `sf`.`Contact`.`Id` = `sf`.`License_Key_Association__c`.`Contact__c`
WHERE
`sf`.`Contact`.`ExternalID__c`='someexternalidhere';
DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_cloud_accounts_records = true;
SELECT
(SELECT `sf`.`Contact`.`CompanyName__c` FROM `sf`.`Contact` WHERE `sf`.`Asset`.`ContactId`=`sf`.`Contact`.`Id`) AS `company`,
`sf`.`License_Key_Association__c`.`License_Key_Status__c` AS `license_status`,
`sf`.`License_Key_Association__c`.`License_Key__c` AS `license_id`,
`sf`.`Asset`.`ContactEmail__c` AS `cloud_owner_email`,
(SELECT `sf`.`Contact`.`CloudEntitlementPlan__c` FROM `sf`.`Contact` WHERE `sf`.`Asset`.`ContactId`=`sf`.`Contact`.`Id`) AS `entitlement_plan`,
`sf`.`License_Key_Association__c`.`Role__c` AS `role`,
IF( (SELECT `sf`.`Product2`.`IsCommercial__c` FROM `sf`.`Product2` WHERE `sf`.`Product2`.`Id`=`sf`.`Asset`.`Product2Id`) = 0,true,false ) AS `is_trial`,
(SELECT
CONCAT('{""',sf.Asset_Attribute__c.Type__c,'"": {',GROUP_CONCAT(
'""',sf.Asset_Attribute__c.Key__c,'"":""',LOWER(sf.Asset_Attribute__c.Value__c),'""'
),'}}')
FROM
sf.Asset_Attribute__c
WHERE
sf.Asset_Attribute__c.Asset__c = license_id
GROUP BY sf.Asset_Attribute__c.Asset__c) AS `license_attributes`
FROM
`sf`.`License_Key_Association__c`
LEFT JOIN `sf`.`Asset`
ON `sf`.`License_Key_Association__c`.`License_Key__c` = `sf`.`Asset`.`Id`
JOIN `sf`.`Contact`
ON `sf`.`Contact`.`Id` = `sf`.`License_Key_Association__c`.`Contact__c`
WHERE
`sf`.`Contact`.`ExternalID__c`=@p_externalId;
OPEN cloud_accounts_cursor;
CLOUDACCOUNTSLOOP: loop
fetch cloud_accounts_cursor into company, license_status, license_id, cloud_owner_email, entitlement_plan, role, is_trial, license_attributes;
IF is_trial = true THEN
SET has_active_subscriptions = true;
END IF;
SET zuora_account_id = `z`.`getZAccountId`(cloud_owner_email);
IF zuora_account_id IS NOT NULL THEN
SELECT `accountNumber`,`status`,`lastInvoiceDate` INTO zuora_account_number,zuora_account_status,zuora_account_last_invoice_date FROM zuora.Account WHERE id=zuora_account_id;
IF has_active_subscriptions = false THEN
SET has_active_subscriptions = (SELECT IF((SELECT COUNT(*) FROM `z`.`RatePlan`
RIGHT JOIN `z`.`ProductRatePlan` ON `z`.`RatePlan`.`productRatePlanId` = `z`.`ProductRatePlan`.`id`
LEFT JOIN `z`.`Subscription` ON `z`.`RatePlan`.`subscriptionId` = `z`.`Subscription`.`id`
WHERE
`z`.`ProductRatePlan`.`wowzaRatePlanCode__c` IN ( (SELECT `code` FROM `z`.`zCloudRatePlanCodes`) )
AND `z`.`Subscription`.`status` = 'Active'
AND `z`.`Subscription`.`accountId` = zuora_account_id ) > 0, true, false));
END IF;
END IF;
REPLACE INTO `sf`.`zCloudAccounts` (`user_email`,`company`,`license_status`,`license_id`,`cloud_owner_email`,`entitlement_plan`,`role`,`is_trial`,`attributes`,`zuora_account_id`,`zuora_account_number`,`zuora_account_status`,`zuora_account_last_invoice_date`,`has_active_subscriptions`) VALUES(@p_userEmail,company,license_status,license_id,cloud_owner_email,entitlement_plan,role,is_trial,license_attributes,zuora_account_id,zuora_account_number,zuora_account_status,zuora_account_last_invoice_date,has_active_subscriptions);
IF no_more_cloud_accounts_records THEN
CLOSE cloud_accounts_cursor;
LEAVE CLOUDACCOUNTSLOOP;
end if;
END LOOP CLOUDACCOUNTSLOOP;
END GETCLOUDACCOUNTS;
如果我在GETCLOUDACCOUNTS块之外执行完全选择状态，我会得到我期望的结果：
company, license_status, license_id, cloud_owner_email, entitlement_plan, role, is_trial, license_attributes
Test Company, Active, 02iq0000000jKgMAAU, myemail@email.com, Standard, Owner, 0, {""cloud"": {""cloud_num_247_t_streams"":""0"",""cloud_num_247_p_streams"":""0""}}
Test Company, Active, 02iq0000000xlBBAAY, otheremail@email.com, Standard, Admin;wcl_admin;wcl_support, 0, {""cloud"": {""cloud_num_247_t_streams"":""1"",""cloud_num_247_p_streams"":""1"",""test_attribute"":""true"",""api_access"":""true""}}
但是块内的结果显示license_attributes为null：
company, license_status, license_id, cloud_owner_email, entitlement_plan, role, is_trial, license_attributes
Test Company, Active, 02iq0000000jKgMAAU, myemail@email.com, Standard, Owner, 0, null
Test Company, Active, 02iq0000000xlBBAAY, otheremail@email.com, Standard, Admin;wcl_admin;wcl_support, 0, null
非常感谢任何帮助！
答案 0 :(得分：1)
我怀疑这个问题与程序变量license_id有关。
SELECT列表中的相关子选择包括
WHERE sf.Asset_Attribute__c.Asset__c = license_id
^^^^^^^^^^
局部变量优先于列引用。由于license_id被声明为代码块中的变量，
DECLARE license_id VARCHAR(18) DEFAULT null;
SELECT语句中对license_id的引用是对该过程变量的引用。
在代码块之外，可能没有名为license_id的局部变量。因此，相同的SQL SELECT语句，对license_id的引用不是对变量的引用，而是对列的引用。
我无法追踪所有逻辑或license_id变量的内容。但我怀疑这解释了在代码块内部和块外部执行的语句所观察到的行为的差异。
答案 1 :(得分：-2)
您可以COALESCE处理GROUP_CONCAT中的NULL值
COALESCE(`YourColumnName`,'')
您还可以使用明显不同的字符串来显示NULL值的来源，以便您可以修复查询。
COALESCE(`YourColumnName`,'**UNEXPECTED NULL**')