mysql - MySQL存储过程，仅在特定条件下更新

Question

存储过程将接受 firstName、lastName、currentPostalCode 和 newPostalCode 作为参数。只有当有一个人具有给定的 firstName、lastName 和 currentPostalCode 时，我才想更新 postalCode 列。

这是怎么做到的？您是否使用子查询或 MySQL IF() 或其他东西？

谢谢。

Answer 1

您不需要任何花哨的条件逻辑来执行此操作，只需UPDATE带有WHERE子句的常规语句即可。WHERE如果子句没有匹配任何行，则不会发生更新。

/* Update the records with matching name & postcode */
UPDATE  yourtable
  SET postalCode = 'newPostalCode'
WHERE
  /* If all 3 conditions don't match, nothing gets updated */
  firstName = 'firstName'
  AND lastName = 'lastName'
  AND postalCode = 'oldPostalCode'

作为存储过程：

CREATE PROCEDURE updatePostalCode (
  IN in_firstName VARCHAR(64),
  IN in_lastName VARCHAR(64),
  IN in_oldPostalCode VARCHAR(16),
  IN in_newPostalCode VARCHAR(16)
)
BEGIN
  UPDATE yourtable 
  SET
    postalCode = in_newPostalCode 
  WHERE 
    lastName = in_lastName 
    AND firstName = in_firstName 
    AND postalCode = in_oldPostalCode;
END

附录：如果你真的只想在只有一个匹配的情况下这样做......

要仅在恰好有一个匹配行（不是 2 个或更多）的情况下更新，您仍然可以使用普通的更新语句，在WHERE子句中添加一个额外的子查询

UPDATE  yourtable
  SET postalCode = 'newPostalCode'
WHERE
  /* If all 3 conditions don't match, nothing gets updated */
  firstName = 'firstName'
  AND lastName = 'lastName'
  AND postalCode = 'oldPostalCode'
  /* Result of count subquery = 1 */
  AND (
    SELECT COUNT(*) AS matched 
    FROM yourtable 
    WHERE firstName = 'firstName' AND lastName = 'lastName' AND postalCode = 'oldPostalCode'
  ) = 1

附录 2 如果不完全匹配则错误退出：

CREATE PROCEDURE updatePostalCode (
  IN in_firstName VARCHAR(64),
  IN in_lastName VARCHAR(64),
  IN in_oldPostalCode VARCHAR(16),
  IN in_newPostalCode VARCHAR(16)
)
BEGIN
  DECLARE num_matched INT;
  SET num_matched = (SELECT COUNT(*) FROM yourtable WHERE firstName = 'firstName' AND lastName = 'lastName' AND postalCode = 'oldPostalCode');

  IF (num_matched <> 1) THEN 
     /* Trigger an error and exit */
     LEAVE updatePostalCode
  END IF

  /* Perform the UPDATE statement */
END