node-mysql multiple statements in one query, execute conditionally on response from each

Question

I want to execute multiple queries in one API call, but I only want to execute them conditionally based on the response of the previous one. How can I go about implementing this?

I've seen that I can do something like below to execute multiple queries.

connection.query('SELECT * ...; SELECT * ...', [1, 2], function(err, results) {
   if (err) throw err;
});

But how do I await the response of the first before conditionally executing the second?

Answer 1

That is not supported (unless written in database itself - like tsql, plsql or others). What you can do - is execute query, wait for its results and then execute another accordingly. example:

const query1 = '.....';
connection.query(query1, [...params1], function(err, results) {
   if (err) throw err;

   const query2 = condition ? '....' : '........';
   connection.query(query2, [...params2], ......);
});

and so on in and in (callback hell).

You can do it a bit better like that (i presume connection is: mysql.getConnection and is properly set without errors there). params<X> is an array with parameters for the query.

const executeQuery = async (con, query, params) {
   return new Promise((resolve, reject) => {
      con.query(query, params, (err, result) => {
          if (err) { return reject(err); }

          return resolve(result);
      });
   });
}


mysql.getConnection((err, connection) => {
   if (err) { throw err; }

   try {
      const query1 = '<some query>';
      const result1 = await executeQuery(query1, params1);

      const query2 = (condition on query1) ? '<query>' : '<other query>';
      const result2 = await executeQuery(connection, query2, params2);

      const query3 = (condition you want) ? '<query for that condition>' : '<or not>';
      const result3 = await executeQuery(connection, query3, params3);
   } catch (err) {
     connection.release();
     throw err;
   } // if newest node  you can use  finally block and have only one  connection.release();

   connection.release();
}