Mysql query doesn't work in qt - mysql

Question

I have written a pretty complex mysql query and test it in mysql workbench, it works very well. But when I use this query in my qt program, it doesn't work.
For better resolution I have 3 tables (products, categories, products_categories) and I want to fetch 3 category with parentId = 5 and 2 product of each category. here is my function:
void DbQueries::getFullCategories(int parent_id, int offset, int limit, int plimit)
{
...
QSqlQuery q;
q.prepare("set #num := 0, #cid := '';"
"SELECT e.ProductId, e.title, e.price, e.rate, e.rateAvg, e.imgUrl, d.cid, d.ctitle"
"FROM products e,"
"(SELECT ProductId, #num := if(#cid = categoryId, #num + 1, 1) as qty, #cid := categoryId as cid, title as ctitle"
"FROM ("
"SELECT b.ProductId, b.categoryId, a.title"
"FROM products_categories b, (SELECT catId, title FROM categories WHERE parentId = :parent_id LIMIT :limit OFFSET :offset) as a"
"WHERE b.categoryId = a.catId"
"ORDER BY b.categoryId"
") as c"
") as d"
"WHERE e.ProductId = d.ProductId AND d.qty <= :plimit"
"ORDER BY d.cid;");
q.bindValue(":parent_id", parent_id);
q.bindValue(":limit", limit);
q.bindValue(":offset", offset);
q.bindValue(":plimit", plimit);
if(!q.exec())
qDebug() << q.lastError().text();
const QSqlRecord &r = q.record();
qDebug() << r.count();
...
}
With this query, after exec() I get no error but there is no record fetched in my QSqlRecord. I tried to put \ before := and I got Unknown escape sequence '\:'.
And when I reduced my query to this:
QSqlQuery q;
q.prepare("SELECT b.ProductId, b.categoryId, a.title"
"FROM products_categories b, (SELECT catId, title FROM categories WHERE parentId = :parent_id LIMIT :limit OFFSET :offset) as a"
"WHERE b.categoryId = a.catId"
"ORDER BY b.categoryId");
I got mysql error like: "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'b, (SELECT catId, title FROM categories WHERE parentId = 5 LIMIT 3 OFFSE' at line 1 QMYSQL: Unable to execute query"

Answer 1

This query has some important white space missing:
"SELECT b.ProductId, b.categoryId, a.title"
"FROM products_categories b, (SELECT catId, title FROM categories WHERE parentId = :parent_id LIMIT :limit OFFSET :offset) as a"
"WHERE b.categoryId = a.catId"
"ORDER BY b.categoryId"
Fix is really simple:
"SELECT b.ProductId, b.categoryId, a.title"
" FROM products_categories b, (SELECT catId, title FROM categories WHERE parentId = :parent_id LIMIT :limit OFFSET :offset) as a"
" WHERE b.categoryId = a.catId"
" ORDER BY b.categoryId"
-^-