不能在 MARIADB 的删除语句中使用 ALIAS答案

【问题标题】：Can't use ALIAS in delete statement in MARIA DB不能在 MARIADB 的删除语句中使用 ALIAS
【发布时间】：2020-03-02 20:02:25
【问题描述】：

我试图从表中删除欺骗，但它不允许我使用别名。尝试了多个论坛中提供的各种解决方案。

查询是，

DELETE FROM `table` AS t1
        WHERE EXISTS (
         SELECT 1 FROM `table` AS t2
         WHERE t2.`col1` = t1.`col1`
         AND t2.`col2` = t1.`col2`
         AND t2.id > t1.id )

【问题讨论】：

标签： mysql mariadb mariasql

【解决方案1】：

您可以尝试使用内部连接而不是存在子查询

DELETE t
FROM `billing_squarecustomer` t
INNER JOIN  (
   SELECT  t2.`patient_id`.
   FROM `billing_squarecustomer` AS t2
   INNER JOIN `billing_squarecustomer` AS t1
   WHERE t2.`patient_id` = t1.`patient_id`
   AND t2.`merchant_id` = t1.`merchant_id`
   AND t2.id > t1.id
) tdel = tdel.patient_id = t.patient_id

【讨论】：

【解决方案2】：

可以使用多表DELETE语句：

DELETE t1 
FROM `table` t1
JOIN `table` t2 ON t2.col1 = t1.col1 AND t2.col2 = t1.col2 AND t2.id > t1.id

【讨论】：

【解决方案3】：

id为primary key时，可以使用left join删除同一张表中的重复项

delete t1
from `table` as t1
left join `table` as t2 on t1.col1 = t2.col1 and t1.col2 = t2.col2 and t1.id < t2.id
where t2.id is not null;

【讨论】：

【解决方案4】：

你可以试试这个，它更复杂但更安全，因为使用内部删除可能非常危险，这样你可以先检查你想删除的内容：

SET @discriminator = 0;
SET @p1 = null;
SET @p2 = null;

CREATE TEMPORARY TABLE temp_rows(
    `id` INT PRIMARY KEY,
    `index` INT,
    `col1` COL1TYPE,
    `col2` COL2TYPE
);

INSERT INTO temp_rows (`index`, `col1`, `col2`, `id`)
SELECT CASE WHEN @p1 != col1 OR @p2 != col2 THEN @discriminator := 0 ELSE @discriminator := @discriminator + 1 END AS 'index', 
    @p1 := col1 AS 'col1', 
    @p2 := col2 AS 'col2',
    id
FROM `schema`.table
ORDER BY col1, col2, id desc;

DELETE FROM table WHERE EXISTS (
     SELECT 1 FROM `temp_rows`
     WHERE table.`id` = temp_rows.`id`
);

DROP TEMPORARY TABLE temp_rows;

【讨论】：