Nested Query in Nodejs Mysql - mysql

Question

I want to count a line in table that has FOO table.
The following code has a bug which show only the last db_name.
RESULT IS LOOK LIKE THIS:
db_0099,0
db_0099,5
db_0099,10
db_0099,3
Could you please suggest me how to fix the nodejs code?
var mysql = require('mysql');
var sql1 = "SELECT table_schema as db_name from information_schema.tables WHERE table_name = 'FOO' ";
var sql2 = "SELECT COUNT(*) as solution FROM {0}.FOO";
var connection = mysql.createConnection({
host : '$$$$$$$',
user : '$$$$$$$',
password : '$$$$$$$',
});
connection.connect(function(err){
console.log('connected as id ' + connection.threadId);
});
connection.query(sql1, function(err, result) {
if (err) throw err;
for (var i = 0, len = result.length; i < len; i++) {
var db_name = result[i].db_name;
console.log(db_name);
connection.query(sql2.replace("{0}",db_name), function(err, result) {
if (err) throw err;
console.log(db_name+','+result[0].solution); //Here db_name is showed only the last one.
});
};
connection.end();
});

Answer 1

i advice a two step solution to this problem:
use connection pooling
var pool = mysql.createPool({
host : 'xxxxx',
user : 'xxxxx',
password : 'xxxxx',
connectionLimit : 100
});
pool can do auto connection, so don't connect to your db, just
pool.query(sql,function(err,res){})
this way you use one connection for each query, which will be closed automatically after using it.
use async await for asyncronous sequential queries.
for that create a getResult function which returns a promise
function getResult(sql){
return new Promise(function(resolve,reject){
pool.query(sql, function(err, result){
if(err){
reject(err)
}else{
resolve(result)
}
})
})
}
then you can await each query in the loop
pool.query(sql1, async function(err, result) {
if (err) throw err;
for (var i = 0; i < result.length; i++) {
var db_name = result[i].db_name;
console.log(db_name);
var sql = sql2.replace("{0}",db_name)
var res = await getResult(sql)
console.log(db_name+','+res[0].solution); //Here db_name is showed only the last one.
};
pool.end()
});
P.S.: async await is a feature of the upcomming node 8.0.0 release in april. for node 7.x you will have to start your script with a commandline switch
node --harmony-async-await yourscript.js

Answer 2

Have you verify the content of result ?
console.log(result);
If it's okay try this :
solutions = results.map(result => {
let dbName = result.db_name;
let queryResult;
connection.query(sql2.replace("{0}", dbName), function(err, result) {
if (err) {
throw err;
} else {
queryResult = `${db_name}, ${result[0].solution}`
console.log(queryResult);
}
});
return queryResult;
})
console.log(solutions);
However, try to use a ORM or a sql parser for your query !
Try this one :)
https://hiddentao.com/squel/