Question

如何在此请求中添加“ordered by created_on asc”：

(select user.first_name as prenom, user.last_name as nom, fvll.created_on, fvll.bar_code, "R" from stk_fuel_voucher_line fvll,stk_fuel_voucher fv, adm_user user 
where YEAR(fvll.created_on)=? and MONTH(fvll.created_on) = ? and user.id=fv.id_user and fv.id=fvll.id_fuel_voucher and
fvll.bar_code not in 
(select fvl.bar_code
from stk_fuel_voucher_line fvl, stk_fuel_voucher_book fvb
where fvl.bar_code >= fvb.first_bar_code and fvl.bar_code <=fvb.last_bar_code
and YEAR(fvl.created_on)=? and MONTH(fvl.created_on) = ?))

UNION

(select user2.first_name as prenom, user2.last_name as nom, fvll2.created_on, fvll2.bar_code, "B"
from stk_fuel_voucher fv2, stk_fuel_voucher_book fvb2, stk_fuel_voucher_line fvll2, adm_user user2 
where fvll2.bar_code >= fvb2.first_bar_code and fvll2.bar_code <=fvb2.last_bar_code and user2.id=fv2.id_user and fv2.id=fvll2.id_fuel_voucher
and YEAR(fvll2.created_on)=? and MONTH(fvll2.created_on) = ?)

Answer 1

在我看来，两个查询是相同的，唯一的区别是检测是否有匹配的bar_code，并返回＆＃39; B＆＃39;或者＆＃39; R＆＃39;根据

我避免了UNION的冗余严重性，只做一个查询，并通过条件测试来确定是否有＆＃39; B＆＃39;或者＆＃39; R＆＃39;归还。

如果UNION运算符（代替更常见的UNION ALL）的意图是从每个集合中删除重复项，我们可以使用GROUP BY子句或{{1} }关键字来实现这一点。（在原始查询中，我们保证两组之间不会重复，总是设置为＆＃39; R＆＃39;，另一组总是有＆＃39; B＆＃39; ;

我不了解查询的规范，但基于我能够从现有查询中辨别的内容，我倾向于做这样的事情：

DISTINCT

同样，如果我们不关心删除重复项，那么我们可以删除SELECT user.first_name AS prenom , user.last_name AS nom , fvll.created_on AS created_on , fvll.bar_code , CASE WHEN ni.bar_code IS NULL THEN 'R' ELSE 'B' END AS r FROM stk_fuel_voucher_line fvll JOIN stk_fuel_voucher fv ON fv.id = fvll.id_fuel_voucher JOIN adm_user user ON user.id = fv.id_user LEFT JOIN ( SELECT fvl.bar_code FROM stk_fuel_voucher_line fvl JOIN stk_fuel_voucher_book fvb ON fvb.first_bar_code <= fvl.bar_code AND fvb.last_bar_code >= fvl.bar_code WHERE YEAR(fvl.created_on) = ? AND MONTH(fvl.created_on) = ? GROUP BY fvl.bar_code ) ni ON ni.bar_code = fvll.bar_code WHERE YEAR(fvll.created_on) = ? AND MONTH(fvll.created_on) = ? GROUP BY user.first_name AS prenom , user.last_name AS nom , fvll.created_on , fvll.bar_code , CASE WHEN ni.bar_code IS NULL THEN 'R' ELSE 'B' END ORDER BY fv11.created_on子句。

对于日期比较，我选择比较原始日期，因此查询可以有效地使用索引范围扫描操作。

而不是：

GROUP BY

我会写类似

的内容

   WHERE YEAR(fvll.created_on)  = ?
     AND MONTH(fvll.created_on) = ?

WHERE fvll.created_on >= month_begin_dt + INTERVAL 0 MONTH AND fvll.created_on >= month_begin_dt + INTERVAL 1 MONTH表示返回该月第一天的表达式，但需要传入，如果我们需要构建一年和一个月的DATE，我们可以这样做。最终目标是等同于：

month_begin_dt

mysql在此请求中排序

1 个答案: