写一段使用C语言的socket编程实现服务器。首先需要在服务器端建立socket，然后监听端口，等待客户端连接。当esp8266连接服务器后，可以使用recv函数接收数据。接收到数据后，可以将数据存储到MySQL数据库中。可以使用C语言的MySQL API实现数据上传操作。

以下是使用C语言的socket编程实现服务器的代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <mysql/mysql.h>

#define PORT 8080
#define MAX_BUFFER_SIZE 1024

int main() {
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[MAX_BUFFER_SIZE] = {0};
    MYSQL *mysql = mysql_init(NULL);

    // Create a socket
    if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    // Set socket options
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt failed");
        exit(EXIT_FAILURE);
    }

    // Bind socket to a specific IP address and port number
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // Listen for incoming connections
    if (listen(server_fd, 3) < 0) {
        perror("listen failed");
        exit(EXIT_FAILURE);
    }

    // Initialize MySQL connection
    if (mysql_real_connect(mysql, "localhost", "username", "password", "database", 0, NULL, 0) == NULL) {
        fprintf(stderr, "%s\n", mysql_error(mysql));
        mysql_close(mysql);
        exit(EXIT_FAILURE);
    }

    // Accept incoming connections
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t *)&addrlen)) < 0) {
        perror("accept failed");
        exit(EXIT_FAILURE);
    }

    // Receive data from the client and store it in the database
    while (1) {
        if ((valread = recv(new_socket, buffer, MAX_BUFFER_SIZE, 0)) <= 0) {
            perror("recv failed");
            exit(EXIT_FAILURE);
        } else {
            printf("Received data: %s", buffer);
            // Insert data into the database
            char query[MAX_BUFFER_SIZE];
            sprintf(query, "INSERT INTO table_name (data) VALUES ('%s')", buffer);
            if (mysql_query(mysql, query)) {
                fprintf(stderr, "%s\n", mysql_error(mysql));
            } else {
                printf("Data inserted!\n");
            }
        }
        memset(buffer, 0, sizeof(buffer)); // Clear the buffer
    }

    // Close connections
    close(new_socket);
    mysql_close(mysql);
    return 0;
}

注意，在实际应用中，我们需要为MySQL数据库设置正确的IP地址、用户名、密码、数据库名称以及数据表名称。另外，上面的代码仅仅是演示如何将数据存储到MySQL数据库中，实际应用中，我们可能还需要对数据进行解析、处理等操作。