需要帮助优化order by和count查询，我有数百万（约300万）行的表。
我必须连接4个表并获取记录，当我运行简单的查询时，它只需要毫秒就可以完成，但是当我试图通过离开连接表来计数或排序时，它会被无限时间卡住。
请看下面的案例。

数据库服务器配置：

CPU Number of virtual cores: 4
Memory(RAM): 16 GiB
Network Performance: High

每个表中的行：

tbl_customers -  #Rows: 20 million.
tbl_customers_address -  #Row 25 million.
tbl_shop_setting - #Rows 50k
aio_customer_tracking - #Rows 5k

表架构：

CREATE TABLE `tbl_customers` (
    `id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    `shopify_customer_id` BIGINT(20) UNSIGNED NOT NULL,
    `shop_id` BIGINT(20) UNSIGNED NOT NULL,
    `email` VARCHAR(225) NULL DEFAULT NULL COLLATE 'latin1_swedish_ci',
    `accepts_marketing` TINYINT(1) NULL DEFAULT NULL,
    `first_name` VARCHAR(50) NULL DEFAULT NULL COLLATE 'latin1_swedish_ci',
    `last_name` VARCHAR(50) NULL DEFAULT NULL COLLATE 'latin1_swedish_ci',
    `last_order_id` BIGINT(20) NULL DEFAULT NULL,
    `total_spent` DECIMAL(12,2) NULL DEFAULT NULL,
    `phone` VARCHAR(20) NULL DEFAULT NULL COLLATE 'latin1_swedish_ci',
    `verified_email` TINYINT(4) NULL DEFAULT NULL,
    `updated_at` DATETIME NULL DEFAULT NULL,
    `created_at` DATETIME NULL DEFAULT NULL,
    `date_updated` DATETIME NULL DEFAULT NULL,
    `date_created` DATETIME NULL DEFAULT NULL,
    PRIMARY KEY (`id`),
    UNIQUE INDEX `shopify_customer_id_unique` (`shopify_customer_id`),
    INDEX `email` (`email`),
    INDEX `shopify_customer_id` (`shopify_customer_id`),
    INDEX `shop_id` (`shop_id`)
)
COLLATE='utf8mb4_general_ci'
ENGINE=InnoDB;

CREATE TABLE `tbl_customers_address` (
    `id` BIGINT(20) NOT NULL AUTO_INCREMENT,
    `customer_id` BIGINT(20) NULL DEFAULT NULL,
    `shopify_address_id` BIGINT(20) NULL DEFAULT NULL,
    `shopify_customer_id` BIGINT(20) NULL DEFAULT NULL,
    `first_name` VARCHAR(50) NULL DEFAULT NULL,
    `last_name` VARCHAR(50) NULL DEFAULT NULL,
    `company` VARCHAR(50) NULL DEFAULT NULL,
    `address1` VARCHAR(250) NULL DEFAULT NULL,
    `address2` VARCHAR(250) NULL DEFAULT NULL,
    `city` VARCHAR(50) NULL DEFAULT NULL,
    `province` VARCHAR(50) NULL DEFAULT NULL,
    `country` VARCHAR(50) NULL DEFAULT NULL,
    `zip` VARCHAR(15) NULL DEFAULT NULL,
    `phone` VARCHAR(20) NULL DEFAULT NULL,
    `name` VARCHAR(50) NULL DEFAULT NULL,
    `province_code` VARCHAR(5) NULL DEFAULT NULL,
    `country_code` VARCHAR(5) NULL DEFAULT NULL,
    `country_name` VARCHAR(50) NULL DEFAULT NULL,
    `longitude` VARCHAR(250) NULL DEFAULT NULL,
    `latitude` VARCHAR(250) NULL DEFAULT NULL,
    `default` TINYINT(1) NULL DEFAULT NULL,
    `is_geo_fetched` TINYINT(1) NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`),
    INDEX `customer_id` (`customer_id`),
    INDEX `shopify_address_id` (`shopify_address_id`),
    INDEX `shopify_customer_id` (`shopify_customer_id`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB;

CREATE TABLE `tbl_shop_setting` (
    `id` INT(11) NOT NULL AUTO_INCREMENT,   
    `shop_name` VARCHAR(300) NOT NULL COLLATE 'latin1_swedish_ci',
     PRIMARY KEY (`id`),
)
COLLATE='utf8mb4_general_ci'
ENGINE=InnoDB;

CREATE TABLE `aio_customer_tracking` (
    `id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    `shopify_customer_id` BIGINT(20) UNSIGNED NOT NULL,
    `email` VARCHAR(255) NULL DEFAULT NULL,
    `shop_id` BIGINT(20) UNSIGNED NOT NULL,
    `domain` VARCHAR(255) NULL DEFAULT NULL,
    `web_session_count` INT(11) NOT NULL,
    `last_seen_date` DATETIME NULL DEFAULT NULL,
    `last_contact_date` DATETIME NULL DEFAULT NULL,
    `last_email_open` DATETIME NULL DEFAULT NULL,
    `created_date` DATETIME NOT NULL,
    `is_geo_fetched` TINYINT(1) NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`),
    INDEX `shopify_customer_id` (`shopify_customer_id`),
    INDEX `email` (`email`),
    INDEX `shopify_customer_id_shop_id` (`shopify_customer_id`, `shop_id`),
    INDEX `last_seen_date` (`last_seen_date`)
)
COLLATE='latin1_swedish_ci'
ENGINE=InnoDB;

正在运行和未运行的查询案例：

1. Running:  Below query fetch the records by joining all the 4 tables, It takes only 0.300 ms.

SELECT `c`.first_name,`c`.last_name,`c`.email, `t`.`last_seen_date`, `t`.`last_contact_date`, `ssh`.`shop_name`, ca.`company`, ca.`address1`, ca.`address2`, ca.`city`, ca.`province`, ca.`country`, ca.`zip`, ca.`province_code`, ca.`country_code`
FROM `tbl_customers` AS `c`
JOIN `tbl_shop_setting` AS `ssh` ON c.shop_id = ssh.id 
LEFT JOIN (SELECT shopify_customer_id, last_seen_date, last_contact_date FROM aio_customer_tracking GROUP BY shopify_customer_id) as t ON t.shopify_customer_id = c.shopify_customer_id
LEFT JOIN `tbl_customers_address` as ca ON (c.shopify_customer_id = ca.shopify_customer_id AND ca.default = 1)
GROUP BY c.shopify_customer_id
LIMIT 20

2. Not running: Simply when try to get the count of these row stuk the query, I waited 10 min but still running.

SELECT 
     COUNT(DISTINCT c.shopify_customer_id)   -- what makes #2 different
FROM `tbl_customers` AS `c`
JOIN `tbl_shop_setting` AS `ssh` ON c.shop_id = ssh.id 
LEFT JOIN (SELECT shopify_customer_id, last_seen_date, last_contact_date FROM aio_customer_tracking GROUP BY shopify_customer_id) as t ON t.shopify_customer_id = c.shopify_customer_id
LEFT JOIN `tbl_customers_address` as ca ON (c.shopify_customer_id = ca.shopify_customer_id AND ca.default = 1)
GROUP BY c.shopify_customer_id
LIMIT 20

3. Not running: In the #1 query we simply put the 1 Order by clause and it get stuck, I waited 10 min but still running. I study query optimization some article and tried by indexing, Right Join etc.. but still not working.

SELECT `c`.first_name,`c`.last_name,`c`.email, `t`.`last_seen_date`, `t`.`last_contact_date`, `ssh`.`shop_name`, ca.`company`, ca.`address1`, ca.`address2`, ca.`city`, ca.`province`, ca.`country`, ca.`zip`, ca.`province_code`, ca.`country_code`
FROM `tbl_customers` AS `c`
JOIN `tbl_shop_setting` AS `ssh` ON c.shop_id = ssh.id 
LEFT JOIN (SELECT shopify_customer_id, last_seen_date, last_contact_date FROM aio_customer_tracking GROUP BY shopify_customer_id) as t ON t.shopify_customer_id = c.shopify_customer_id
LEFT JOIN `tbl_customers_address` as ca ON (c.shopify_customer_id = ca.shopify_customer_id AND ca.default = 1)
GROUP BY c.shopify_customer_id
  ORDER BY `t`.`last_seen_date`    -- what makes #3 different
LIMIT 20

解释问题1：

解释问题2：

解释问题3：

欢迎提出优化查询、表结构的建议。

我想做的是： tbl_customers 表包含客户信息， tbl_customer_address 表包含客户的地址（一个客户可能有多个地址），以及 aio_customer_tracking 表包含客户的访问记录 last_seen_date 是访问日期。

现在，我只想获取和统计客户，以及他们的地址和访问信息。另外，我可以按这3个表中的任何列排序，在我的示例中，我是按上次看到的日期排序（默认顺序）。希望这个解释有助于理解我在做什么。