Mysql 称为逻辑查询处理，这意味着在查询FROM语句中，首先计算和处理查询，然后处理查询的其余部分。在LQP术语中，查询将按以下顺序处理。{FROM-->其中-->GROUP BY-->HAVING-->SELECT-->ORDER BY}因此，SELECT子句中

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称为逻辑查询处理，这意味着在查询FROM语句中，首先计算和处理查询，然后处理查询的其余部分。在LQP术语中，查询将按以下顺序处理。{FROM-->其中-->GROUP BY-->HAVING-->SELECT-->ORDER BY}因此，SELECT子句中的别名仅用于更相关的结果，因此列可以有更合适的名称。有时回答问题还不够+1。有时回答问题还不够+1。

SELECT c.remaining_budget, 
       c.future_liabilities, 
       c.used_this_month, 
       bi.full_name, 
       bi.id                                                             AS 
       item_id, 
       (SELECT Sum(amount) 
        FROM   balance_histories 
        WHERE  balance_histories.budget_item_id = 21 
               AND Date_format(payment_date, '%Y-%m-01') = '2018-01-01') AS 
       monthly_usage 
FROM   families_budget_items_calcs c 
       LEFT JOIN budget_items bi 
              ON c.budget_item_id = bi.id 
WHERE  c.family_id = 54824 
       AND bi.id IN ( 21 ) 
       AND monthly_usage <> 0  

WHERE
    c.family_id = 54824 AND
    bi.id IN ( 21 )
HAVING
    monthly_usage <> 0

SELECT c.remaining_budget, c.future_liabilities, c.used_this_month, 
       bi.full_name, bi.id as item_id,
       (SELECT Sum(bh.amount) 
        FROM balance_histories bh
        WHERE bh.budget_item_id = 21 AND
              payment_date >= '2018-01-01' AND
              payment_date < '2018-02-01'
       ) as monthly_usage 
FROM families_budget_items_calcs c INNER JOIN
     budget_items bi 
     ON c.budget_item_id = bi.id 
WHERE c.family_id = 54824 AND
      bi.id IN ( 21 ) 
HAVING monthly_usage <> 0 ;