MySQL如果不存在，则会在存储过程中给我一个错误

Question

我在使用mysql phpmyadmin具有以下存储过程：

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 ，我会遇到2个错误：

1. 无法识别的关键字。 （ 如果不存在附近）
2. 意外的标记。 （近（）

Answer 1

就个人而言，如果我需要编写一个执行指定操作并返回结果集的过程，则可以这样编写：

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，则无需运行两个SELECT语句。 我们可以做该行的检查， 并得到一个单一的ADDRESS_ID SELECT 。

如果没有得到匹配的行，则插入一行，并获取自动增量ID。

无论哪种情况（找到的行或添加的行），都将address_id作为结果集返回。 同样，我们可以使用单个SELECT语句而不是两个不同的语句来完成此操作。

对我来说，限制返回结果集的位置数和限制查询数据库的次数更有意义。