Mysql查詢在qt中不起作用

我寫了一個非常複雜的mysql查詢並在mysql工作臺中測試它，它工作得很好。但是當我在我的qt程序中使用這個查詢時，它不起作用。Mysql查詢在qt中不起作用

爲了獲得更好的分辨率，我有3個表格（產品，類別，產品類別），我想用parentId = 5和每個類別的2個產品獲取3個類別。這裏是我的功能：

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(); 

    ... 
}

與此查詢，exec()後，我沒有錯誤，但沒有記錄在我的QSqlRecord牽強。我試圖在:=之前放\，並且我得到了Unknown escape sequence '\:'。

當我我的查詢減少到這一點：

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");

我有mysql的錯誤，如："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"

來源

2017-02-16 ineptant

這有點混亂。重來。並參見http://meta.stackoverflow.com/questions/333952/why-should-i-provide-an-mcve-for-what-seems-to-me-to-be-a-very-simple-sql-詢問 – Strawberry

這個查詢有一些重要的空白丟失：

 "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"

修復是真的簡單：

 "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" 
     -^-

來源

2017-02-16 11:40:16

Mysql查詢在qt中不起作用

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