mysql - 如何在mysql中根据特定条件查找特定月份？

Question

我正在尝试解决一个 mysql 任务。下面是我的sql查询的目标 “显示 2017 年所有月份申请的客户数量 贷款比当年月平均客户数高出20%。”

我正在尝试使用此查询来解决此任务:

SELECT monthname(created_date) 
FROM customers 
WHERE year(2017) 
  and count(customer_id) >= 0.2 * avg(count(costumers))

我尝试在 stackoverflow 中搜索答案，但没有一个可以回答我的问题。

下面是表结构:

我使用的是 MYSQL 8

这是我的 SQL 转储:

-- MySQL dump 10.13  Distrib 8.0.17, for Win64 (x86_64)
--
-- Host: localhost    Database: marketplace
-- ------------------------------------------------------
-- Server version 8.0.17

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!50503 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

--
-- Table structure for table `banks`
--

DROP TABLE IF EXISTS `banks`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!50503 SET character_set_client = utf8mb4 */;
CREATE TABLE `banks` (
  `bank_id` int(11) NOT NULL,
  `bank_name` tinytext,
  PRIMARY KEY (`bank_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `banks`
--

LOCK TABLES `banks` WRITE;
/*!40000 ALTER TABLE `banks` DISABLE KEYS */;
INSERT INTO `banks` VALUES (1,'HSBC'),(2,'Ocean Bank'),(3,'BCA'),(4,'BRI'),(5,'BNI'),(6,'BTPN'),(7,'Bank Keadilan');
/*!40000 ALTER TABLE `banks` ENABLE KEYS */;
UNLOCK TABLES;

--
-- Table structure for table `customers`
--

DROP TABLE IF EXISTS `customers`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!50503 SET character_set_client = utf8mb4 */;
CREATE TABLE `customers` (
  `costumer_id` int(11) NOT NULL,
  `customer_name` text,
  `customer_age` int(11) DEFAULT NULL,
  `estimated_risk_level` text,
  `source` text,
  `created_date` datetime DEFAULT NULL,
  PRIMARY KEY (`costumer_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `customers`
--

LOCK TABLES `customers` WRITE;
/*!40000 ALTER TABLE `customers` DISABLE KEYS */;
INSERT INTO `customers` VALUES (1,'najib',45,'high','facebook','2019-08-13

09:27:52'),(2,'ridho',19,'low','google','2019-08-13 09:27:52'),(3,'ujang',25,'high','facebook','2019-08-13 09:27:52'),(4,'nadya',23,'medium','instagram','2019-08-13 09:27:52'),(5,'uli',22,'medium','google','2019-08-13 09:27:52'),(6,'syahputra',35,'low','google','2019-08-13 09:27:52'); /*!40000 ALTER TABLE customers ENABLE KEYS */; UNLOCK TABLES;

--
-- Table structure for table `leads`
--

DROP TABLE IF EXISTS `leads`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!50503 SET character_set_client = utf8mb4 */;
CREATE TABLE `leads` (
  `customer_id` int(11) NOT NULL,
  `product_id` int(11) DEFAULT NULL,
  `apply_date` datetime DEFAULT NULL,
  PRIMARY KEY (`customer_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `leads`
--

LOCK TABLES `leads` WRITE;
/*!40000 ALTER TABLE `leads` DISABLE KEYS */;
INSERT INTO `leads` VALUES (1,2,'2019-08-14 09:27:52'),(2,1,'2019-08-14 09:27:52'),(4,6,'2019-08-14

09:27:52'),(5,5,'2019-08-14 09:27:52'),(6,4,'2019-08-14 09:27:52'); /*!40000 ALTER TABLE leads ENABLE KEYS */; UNLOCK TABLES;

--
-- Table structure for table `products`
--

DROP TABLE IF EXISTS `products`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!50503 SET character_set_client = utf8mb4 */;
CREATE TABLE `products` (
  `product_id` int(11) NOT NULL,
  `loan_amount` int(11) DEFAULT NULL,
  `interest_rate` float DEFAULT NULL,
  `accepted_risk_level` text,
  `bank_id` int(11) DEFAULT NULL,
  `created_date` datetime DEFAULT NULL,
  PRIMARY KEY (`product_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `products`
--

LOCK TABLES `products` WRITE;
/*!40000 ALTER TABLE `products` DISABLE KEYS */;
INSERT INTO `products` VALUES (1,1500,2.5,'low',1,'2019-08-13 09:27:52'),(2,2000,2.5,'high',1,'2019-08-13

09:27:52'),(3,1200,5,'high',1,'2019-08-13 09:27:52'),(4,2500,2.5,'medium',2,'2019-08-13 09:27:52'),(5,1550,5,'medium',2,'2019-08-13 09:27:52'); /*!40000 ALTER TABLE products ENABLE KEYS /; UNLOCK TABLES; /!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

-- Dump completed on 2019-08-13 22:31:35

Answer 1

SQL DEMO

第一步检查每月有多少客户申请贷款:

SELECT COUNT(customer_id) as monthly_count
FROM leads
WHERE year(apply_date) = 2019
GROUP BY MONTH(apply_date);

monthly_count
1
4

现在您可以计算该月的平均申请量:

SELECT AVG(monthly_count) as loans_avg
FROM (
    SELECT COUNT(customer_id) as monthly_count
    FROM leads
    WHERE year(apply_date) = 2019
    GROUP BY MONTH(apply_date)
) t

loans_avg
2.5000

现在您可以将每月计数与平均值进行比较:

WITH monthly_avg as  (
    SELECT AVG(monthly_count) as loans_avg
    FROM (
        SELECT COUNT(customer_id) as monthly_count
        FROM leads
        WHERE year(apply_date) = 2019
        GROUP BY MONTH(apply_date)
        ) t
)
SELECT monthname(apply_date), COUNT(customer_id) as monthly_count
FROM leads
WHERE year(apply_date) = 2019
GROUP BY monthname(apply_date)
HAVING monthly_count > (SELECT 1.2 * loans_avg
                        FROM monthly_avg)


monthname(apply_date)   monthly_count
July                       4

在这种情况下，只有 7 月高于1.2 * 平均值