Question

表格：

CREATE TABLE `vendor_contacts` (
  `vendor_id` int(11) NOT NULL,
  `last_name` varchar(50) NOT NULL,
  `first_name` varchar(50) NOT NULL,
  `name_initials` varchar(45),
  PRIMARY KEY (`vendor_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

使用以下insert语句：

INSERT INTO `vendor_contacts`
    VALUES (5,'Davison','Michelle',''),
           (12,'Mayteh','Kendall',''),
           (17,'Onandonga','Bruce',''),
           (44,'Antavius','Anthony',''),
           (76,'Bradlee','Danny',''),
           (94,'Suscipe','Reynaldo',''),
           (101,'O\'Sullivan','Geraldine',''),
           (123,'Bucket','Charles','');

我正在尝试使用以下命令分配列，name_initials，派生自PostgreSQL [Update＆gt; Set＆gt; From]：

UPDATE vendor_contacts
SET name_initials = t.initials
FROM (
        SELECT vendor_id, last_name, first_name,
            CONCAT(LEFT(first_name, 1), LEFT(last_name, 1)) as initials
        FROM vendor_contacts;
) t 
WHERE vendor_id = t.vendor_id;

由于这不起作用，我尝试了Oracle SQL Merge Into：

MERGE INTO vendor_contacts
USING (
        SELECT vendor_id, last_name, first_name,
            CONCAT(LEFT(first_name, 1), LEFT(last_name, 1)) as initials
        FROM vendor_contacts;
      ) t
ON (vendor_id = t.vendor_id)
WHEN matched THEN
    UPDATE SET name_initials = t.initials;

MERGE不起作用。

我尝试了一个子查询，它也不起作用：

UPDATE vendor_contacts vc
SET name_initials = (SELECT CONCAT(LEFT(first_name, 1), LEFT(last_name, 1))
                     FROM vendor_contacts vcsq
                     WHERE vcsq.vendor_id = vc.vendor_id);

Answer 1

为什么所有这些并发症，为什么不呢？

UPDATE vendor_contacts 
SET name_initials = CONCAT(LEFT(first_name, 1), LEFT(last_name, 1));

它根据其他列的值设置首字母字段。

但即使这个查询也是你不应该运行的东西。正确的做法是删除name_initials列。你不需要它。因为它是简单计算的结果，通常不会为简单计算创建列。您可以使用生成的列，也可以使用简单的。

SELECT *, 
CONCAT(LEFT(first_name, 1), LEFT(last_name, 1)) AS name_initials FROM vendor_contacts;

MySQL相当于执行UPDATE SET FROM / MERGE INTO

1 个答案: