Selects from multiple tables for Activities feed - sql-server

Question

I have a social app for which I am trying to create a friend activities feed using Azure Sql Server.
I have 3 tables I want to select from:
Songs
-createdAt
-id
-userId
-trackName
-etc
Comments
-createdAt
-id
-userId
-songId
-text
Likes
-createdAt
-id
-userId
-songId
I have the users that the current user is following stored in an array named 'follows'.
How do I go about selecting the 40 most recent items from those 3 tables where userId in each table is in the follows array?
Edit:
function getActivities(userId) {
var deferred = Q.defer();
var follows = [];
getFollowing(userId).then(function (results) {
follows.push(userId);
_.each(results, function (user) {
follows.push(user.toUserId);
});
return;
}).then(function () {
var stringified = "'" + follows.join("','") + "'";
var queryString = "SELECT * FROM comments, songs, likes WHERE comments.userId IN (" + stringified + ") OR songs.userId IN (" + stringified +") OR likes.userId IN (" + stringified + ")";
var params = [];
return sqlQuery(queryString, params);
}).then(function (results) {
console.log('Activities: ', results);
deferred.resolve(results);
}, function (error) {
console.log('Error: ', error.message);
deferred.reject(error.message);
});
return deferred.promise;
}

Answer 1

Alright, so I dug into JOINS a little more and realized how easy it actually is once you wrap your head around it. Here is what I did to complete this:
var queryString = "SELECT TOP 50 follows.id AS followId, follows.toUserId AS followToUserId, follows.fromUserId AS followFromUserId, comments.text AS commentText, profiles.userId, profiles.username, profiles.name, profiles.profileImage, songs.trackId, songs.trackName, songs.artistName, songs.collectionName, songs.artworkUrl100, songs.caption, songs.id AS songId, activities.id AS activityId, activities.type AS activityType, activities.objectId AS activityObjectId, activities.parentType AS activityParentType, activities.parentId AS activityParentId, activities.__createdAt AS activityCreatedAt FROM activities ";
queryString += "INNER JOIN profiles ON (profiles.userId = activities.userId) ";
queryString += "LEFT JOIN songs ON (songs.id = activities.objectId AND activities.type = 'songs') OR (songs.id = activities.parentId AND activities.parentType = 'songs') ";
queryString += "LEFT JOIN comments ON (activities.type = 'comments' AND comments.id = activities.objectId) ";
queryString += "LEFT JOIN follows ON (activities.type = 'followed' AND activities.userid = follows.fromUserId) ";
queryString += "WHERE activities.userId IN (SELECT follows.toUserId AS userId FROM follows WHERE follows.fromUserId = ? AND follows.isFollowed = 'true') ";
queryString += "ORDER BY activities.__createdAt DESC";
var params = [userId];
mssql.query(queryString, params, {
success: function (results) {
_.each(results, function (result) {
//Remove columns with null or undefined values
for (var i in result) {
if (result[i] === null || result[i] === undefined) {
delete result[i];
}
}
});
response.send(200, results);
},
error: function (error) {
response.send(400, error.message);
}
});