MySQL如果不存在，則會在存儲過程中給我一個錯誤

Question

我在使用mysql phpmyadmin具有以下存儲過程：

CREATE DEFINER=`user`@`localhost` PROCEDURE `set_address`(IN `patient_street` VARCHAR(128), IN 
`patient_city` VARCHAR(45), IN `patient_post_code` VARCHAR(45), IN `patient_state_or_province` VARCHAR(45), IN `patient_country` VARCHAR(45)) 
NOT DETERMINISTIC NO SQL SQL SECURITY 
DEFINER 
BEGIN 
IF NOT EXISTS (SELECT a.address_id FROM address as a where a.street = patient_street and a.city = patient_city and a.post_code = patient_post_code and a.country = patient_country) 
THEN 
BEGIN 
INSERT INTO address (street, city, post_code, state_or_province, country) VALUES (patient_street, patient_city, patient_post_code, patient_state_or_province, patient_country); 
SELECT LAST_INSERT_ID(); 
END; 
ELSE 
BEGIN 
SELECT a.address_id FROM address as a where a.street = patient_street and a.city = patient_city and a.post_code = patient_post_code and a.country = patient_country 
END; 
END IF; 
END;

但是， IF NOT EXISTS ，我會遇到2個錯誤：

1. 無法識別的關鍵字。 （ 如果不存在附近）
2. 意外的標記。 （近（）

Answer 1

就個人而言，如果我需要編寫一個執行指定操作並返回結果集的過程，則可以這樣編寫：

DELIMITER $$

CREATE DEFINER=`user`@`localhost` PROCEDURE `set_address`
(IN `patient_street`            VARCHAR(128)
,IN `patient_city`              VARCHAR(45)
,IN `patient_post_code`         VARCHAR(45)
,IN `patient_state_or_province` VARCHAR(45)
,IN `patient_country`           VARCHAR(45)
)
NOT DETERMINISTIC SQL SECURITY DEFINER
BEGIN
  DECLARE li_address_id BIGINT DEFAULT NULL;
  -- check for existing row and get address_id
  SELECT a.address_id
    INTO li_address_id
    FROM address a
   WHERE a.street    = patient_street
     AND a.city      = patient_city
     AND a.post_code = patient_post_code
     AND a.country   = patient_country
   LIMIT 1 ;
  -- if we didn't find a matching row
  IF li_address_id IS NULL THEN
    -- add a row and get the new address_id
    INSERT INTO address (street, city, post_code, state_or_province, country) VALUES
    (patient_street, patient_city, patient_post_code, patient_state_or_province, patient_country);
    SELECT LAST_INSERT_ID() INTO li_address_id;
  END IF;

  -- return address_id (either found existing row, or newly added row) as a resultset
  SELECT li_address_id AS address_id;
END$$

DELIMITER ;

---

如果存在一行，則無需運行兩個SELECT語句。 我們可以做該行的檢查， 並得到一個單一的ADDRESS_ID SELECT 。

如果沒有得到匹配的行，則插入一行，並獲取自動增量ID。

無論哪種情況（找到的行或添加的行），都將address_id作為結果集返回。 同樣，我們可以使用單個SELECT語句而不是兩個不同的語句來完成此操作。

對我來說，限制返回結果集的位置數和限制查詢數據庫的次數更有意義。