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joplin notion extension/Web Development/nodejs/mysql connect.md

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+mysql connect
+
+Install it first using `npm i mysql2` as mysql v1 may have some issues
+```js
+
+const mysql = require("mysql");
+
+const con = mysql.createConnection({
+  host: "localhost",
+  user: "root",
+  password: "password",
+  database: "hospitals",
+  multipleStatements: true,
+});
+
+app.post("/register", (req, res) => {
+  const { name, address, email, phone_no, password } = req.body;
+  const { patient_photo } = req.files;
+  const patientPhotoPathname = patient_photo.path;
+
+	
+	  // Store the registration details
+  con.query(
+    `use hospitals;
+    insert into patients(name,address,email,phone_no,password,patient_photo_path)
+    values ('${name}','${address}','${email}','${phone_no}','${password}','${patientPhotoPathname}')
+        `,
+    (err, result) => {
+      if (err) {
+        console.log(err);
+
+        res
+          .status(400)
+          .json("Error while registering. Email address must be unique");
+      } else {
+        console.log(result);
+        res.json("Registered");
+      }
+    }
+  );
+}
+	
+	app.get("/fetch", (req, res) => {
+  const { hospital_id } = req.body;
+	
+	 // console.log("body:", req.body);
+  const sqlquery = `select hospital_id,count(psychiatrists.id) as  psychiatrist_count,
+  sum(patients_count) as total_patients_count,hospital.name
+  from psychiatrists,hospital
+  where hospital.id=psychiatrists.hospital_id and hospital_id=${hospital_id};
+  select id,name,patients_count from psychiatrists
+  where hospital_id=${hospital_id};
+  `;
+
+  con.query(sqlquery, (err, result) => {
+    if (err) {
+      res.status(500).json("Some error while fetching");
+      console.log(err);
+      return;
+    }
+
+    console.log(result);
+}
+```
+
+- handling disconnection due to idle timeout
+  ```js
+	function handleDisconnect() {
+  con = mysql.createConnection(dbConfig); // Recreate the connection, since the old one cannot be reused.
+  con.connect(function onConnect(err) {
+    // The server is either down
+    if (err) {
+      // or restarting (takes a while sometimes).
+      console.log("error when connecting to db:", err);
+      setTimeout(handleDisconnect, 10000); // We introduce a delay before attempting to reconnect,
+    } // to avoid a hot loop, and to allow our node script to
+  }); // process asynchronous requests in the meantime.
+  // If you're also serving http, display a 503 error.
+  con.on("error", function onError(err) {
+    console.log("db error", err);
+    // if (err.code == "PROTOCOL_CONNECTION_LOST") {
+    //   // Connection to the MySQL server is usually
+    //   handleDisconnect(); // lost due to either server restart, or a
+    // } else {
+    //   // connnection idle timeout (the wait_timeout
+    //   throw err; // server variable configures this)
+    // }
+    handleDisconnect();
+  });
+	}
+	handleDisconnect();
+
+	con.on("connection", () => {
+	  console.log("db connected");
+	});
+
+	```