MySql在同一表上的多个联接-获得多个分类帐/钱包的期末余额

问题描述

transactions表模式：

--------------------------------------
| user_id | currency | amount | date |
--------------------------------------
|       1 |      eur |    500 | ...  |
|       1 |      gbp |    100 | ...  |
|       1 |      usd |     10 | ...  |
|       1 |      usd |     10 | ...  |
|       1 |      gbp |    100 | ...  |
|       1 |      usd |     10 | ...  |
|       1 |      usd |     10 | ...  |
|       2 |      jpy |     99 | ...  |
|       1 |      jpy |     99 | ...  |
--------------------------------------

我想要什么：

-----------------------------------
|         | total balances        |
| user_id | eur | usd | gbp | jpy |
-----------------------------------
|       1 | 500 |  40 | 200 |  99 |
|       2 |   0 |   0 |   0 |  99 |
-----------------------------------

我的查询代码（使用Laravel的雄辩的ORM）：

$query = DB::table('users AS u')
    ->join ('transactions AS t1','t1.user_id','=','u.id')
    ->where('t1.currency','eur')
    ->join ('transactions AS t2','t2.user_id','u.id')
    ->where('t2.currency','usd')
    ->join ('transactions AS t3','t3.user_id','u.id')
    ->where('t3.currency','gbp')
    ->join ('transactions AS t4','t4.user_id','u.id')
    ->where('t4.currency','jpy')
    ->selectRaw('
        u.id AS u_id,u.username AS u_username,SUM(t1.amount) AS total_eur,SUM(t2.amount) AS total_usd,SUM(t3.amount) AS total_gbp,SUM(t4.amount) AS total_jpy
    ')
    ->groupBy('u.id');

dd($query->get());

产生的SQL：

select 
      SUM(t1.amount) AS total_eur,SUM(t2.amount) AS total_gbp,SUM(t3.amount) AS total_usd,SUM(t4.amount) AS total_jpy,u.id AS u_id,u.username AS u_username
      
   from `users` as `u` 
   left join `transactions` as `t1` on `t1`.`user_id` = `u`.`id`
   left join `transactions` as `t2` on `t2`.`user_id` = `u`.`id`
   left join `transactions` as `t3` on `t3`.`user_id` = `u`.`id` 
   left join `transactions` as `t4` on `t4`.`user_id` = `u`.`id` 
   
   where `t1`.`wallet_type` = 'eur'
     and `t2`.`wallet_type` = 'gbp'
     and `t3`.`wallet_type` = 'usd'
     and `t3`.`wallet_type` = 'jpy'

   group by `u`.`id`

使用3个或更多联接（transactions表只有约600行）时，非常慢
当我仅使用两种货币/仅使用两次联接时，速度非常快（不到1秒）

我认为多次连接同一张表是一个坏习惯。
有什么方法可以优化查询？

解决方法

您需要类似的东西

$query = DB::table('users AS u')
    ->join ('transactions AS t1','t1.user_id','=','u.id')
    ->selectRaw('
        u.id AS u_id,u.username AS u_username,SUM(CASE WHEN t1.currency = \'eur\' THEN t1.amount END) AS total_eur,SUM(CASE WHEN t1.currency = \'usd\' THEN t1.amount END) AS total_usd,SUM(CASE WHEN t1.currency = \'gbp\' THEN t1.amount END) AS total_gbp,SUM(CASE WHEN t1.currency = \'jpy\' THEN t1.amount END) AS total_jpy
    ')
    ->groupBy('u.id');

检查语法-我不使用Laravel。

如果某些用户数据中未列出某种货币，则将为NULL。如果需要零，则将表达式扩展到CASE WHEN t1.currency = \'xxx\' THEN t1.amount ELSE 0 END