选择加入2个表和两个表的最新记录答案

【问题标题】：select join 2 tables and latest records of both tables选择加入2个表和两个表的最新记录
【发布时间】：2022-01-16 11:59:02
【问题描述】：

我有 2 张桌子，而且很热。我需要为每个 symbol_id 选择加入两个表的最新记录

SELECT
    `board`.`id`,
    `board`.`symbol_id`,
    `board`.`symbol`,
    `board`.`t_volume`,
    `board`.`unix_timestamp`,
    `board`.`time`,
    `board`.`date`,
    `hot`.`id`,
    `hot`.`time`,
    `hot`.`date`,
    `hot`.`buy_repeat`,
    `hot`.`sell_repeat`
FROM `board` 
LEFT JOIN `hot`
    ON `hot`.`symbol_id` = `board`.`symbol_id`
WHERE  `board`.`unix_timestamp` = (
    SELECT `board`.`unix_timestamp`
    FROM `board`
    ORDER BY unix_timestamp DESC
    LIMIT 1
)
AND `board`.`symbol_id` = '34557241988629814'
GROUP BY `hot`.`symbol_id`
ORDER BY `hot`.`id` DESC

【问题讨论】：

标签： mysql join select subquery

【解决方案1】：

您的问题缺乏详细信息（MySQL 版本、表声明、示例数据和预期输出示例），但我认为这就是您要寻找的。p>

这适用于 MySQL

两个子查询使用 LEFT JOIN ... IS NULL 技术来获取每个 symbol_id 的最新（按 id）记录。然后，根据您的尝试，派生表是左联接的。

SELECT

    `b_latest`.`id`,
    `b_latest`.`symbol_id`,
    `b_latest`.`symbol`,
    `b_latest`.`t_volume`,
    `b_latest`.`unix_timestamp`,
    `b_latest`.`time`,
    `b_latest`.`date`,

    `h_latest`.`id`,
    `h_latest`.`time`,
    `h_latest`.`date`,
    `h_latest`.`buy_repeat`,
    `h_latest`.`sell_repeat`

FROM (
    SELECT
        `b1`.`id`,
        `b1`.`symbol_id`,
        `b1`.`symbol`,
        `b1`.`t_volume`,
        `b1`.`unix_timestamp`,
        `b1`.`time`,
        `b1`.`date`
    FROM board b1
    LEFT JOIN board b2 ON (b1.symbol_id = b2.symbol_id AND b1.id < b2.id)
    WHERE b2.id IS NULL
) AS b_latest
LEFT JOIN (
    SELECT
        `h1`.`id`,
        `h1`.`symbol_id`
        `h1`.`time`,
        `h1`.`date`,
        `h1`.`buy_repeat`,
        `h1`.`sell_repeat`
    FROM hot h1
    LEFT JOIN hot h2 ON (h1.symbol_id = h2.symbol_id AND h1.id < h2.id)
    WHERE h2.id IS NULL
) AS h_latest
    ON b_latest.symbol_id = h_latest.symbol_id

对于 MySQL 8.0 及更高版本，您可以使用 Window Functions -

WITH `b_latest` AS (
    SELECT
        `b1`.`id`,
        `b1`.`symbol_id`,
        `b1`.`symbol`,
        `b1`.`t_volume`,
        `b1`.`unix_timestamp`,
        `b1`.`time`,
        `b1`.`date`,
        ROW_NUMBER() OVER (PARTITION BY `symbol_id` ORDER BY `id` DESC) AS `rn`
    FROM `board` `b1`
), `h_latest` AS (
    SELECT
        `h1`.`id`,
        `h1`.`symbol_id`
        `h1`.`time`,
        `h1`.`date`,
        `h1`.`buy_repeat`,
        `h1`.`sell_repeat`,
        ROW_NUMBER() OVER (PARTITION BY `symbol_id` ORDER BY `id` DESC) AS `rn`
    FROM `hot` `h1`
)
SELECT

    `b_latest`.`id`,
    `b_latest`.`symbol_id`,
    `b_latest`.`symbol`,
    `b_latest`.`t_volume`,
    `b_latest`.`unix_timestamp`,
    `b_latest`.`time`,
    `b_latest`.`date`,

    `h_latest`.`id`,
    `h_latest`.`time`,
    `h_latest`.`date`,
    `h_latest`.`buy_repeat`,
    `h_latest`.`sell_repeat`

FROM `b_latest`
LEFT JOIN `h_latest`
    ON `b_latest`.`symbol_id` = `h_latest`.`symbol_id`
    AND `h_latest`.`rn` = 1
WHERE `b_latest`.`rn` = 1

【讨论】：