➡️ 查重

SELECT
    *
FROM
    order_log ol
WHERE
    (ol.order_id, ol.`desc`) IN (
        SELECT
            order_id,
            `desc`
        FROM
            order_log
        GROUP BY
            order_id,
            `desc`
        HAVING
            count(*) > 1
    )

注意：
会报错You can't specify target table 'xxx' for update in FROM clause
解决办法：一定要给最里面的子查询定义一个别名

https://www.cnblogs.com/jiangxiaobo/p/6589541.html

➡️ 查询数据库中表的字段个数

检查表结构时有用

SELECT table_name,COUNT(*) FROM information_schema.columns
WHERE table_schema = 'hebcf'
GROUP BY table_name
ORDER BY table_name ASC

➡️ 地区名称更新为简称

## 省份
UPDATE table SET province=REPLACE (province,'省','');
UPDATE table SET province=REPLACE (province,'市','');
UPDATE table SET province='广西' WHERE province='广西壮族自治区';
UPDATE table SET province='新疆' WHERE province='新疆维吾尔自治区';
UPDATE table SET province='内蒙古' WHERE province='内蒙古自治区';
UPDATE table SET province='宁夏' WHERE province='宁夏回族自治区';

➡️ 查看表字段

https://stackoverflow.com/questions/1526688/get-table-column-names-in-mysql/1526722