Question

在我的项目中，有几个很长的SQL语句。它们超过100行，多个选择，连接和嵌套联合。它很难阅读，有必要进行优化。我应该注意哪个方面？表结构，SQL语句本身还是其他什么？如何优化这些长SQL语句？欢迎任何建议。

以下是一段代码。

select p.id,p.from_zone fromzone,p.to_zone tozone,p.action,p.status,saw.srcaddr,daw.dstaddr,aw2.protocol,case when aw2.port=';' then ' ' else aw2.port end port                            
from policy p join (select sa.id,sa.device,concat(replace(group_concat(sa.nameshow),',',';&lt;br /&gt;'),';') srcaddr from                                          
                                (select sai.id,sai.device,sai.nameshow,max(sai.flag) flagw from
                                        (select psa1.id,psa1.device,a1.network nameshow,case when a1.from_network&lt;=#{srcAddr} and a1.to_network&gt;=#{srcAddr} then 1 else 0 end flag from policy_source_destination_addr psa1 join address a1 on psa1.address=a1.name and psa1.device=a1.device and psa1.zone=a1.zone where psa1.device=#{deviceName} and psa1.direction='source'
                                         union
                                         select psa2.id,psa2.device,psa2.address nameshow,case when a2.from_network&lt;=#{srcAddr} and a2.to_network&gt;=#{srcAddr} then 1 else 0 end flag from policy_source_destination_addr psa2 join address_set as1 on psa2.address=as1.name and psa2.device=as1.device and psa2.zone=as1.zone
                                                                                join address a2 on as1.device=a2.device and as1.zone=a2.zone and as1.address=a2.name
                                                                                where psa2.device=#{deviceName} and psa2.direction='source'
                                         union
                                         select psa3.id,psa3.device,psa3.address nameshow,case when a5.from_network&lt;=#{srcAddr} and a5.to_network&gt;=#{srcAddr} then 1 else 0 end flag from policy_source_destination_addr psa3 join address_set as3 on psa3.address=as3.name and psa3.device=as3.device and psa3.zone=as3.zone
                                                                                join address_set as4 on as3.device=as4.device and as3.zone=as4.zone and as3.address=as4.name
                                                                                join address a5 on as4.device=a5.device and as4.zone=a5.zone and as4.address=a5.name
                                                                                where psa3.device=#{deviceName} and psa3.direction='source'
                                         union
                                         select psa3.id,psa3.device,psa3.address nameshow,1 flag from policy_source_destination_addr psa3 where psa3.device=#{deviceName} and psa3.direction='source' and upper(psa3.address)='ANY'
                                         ) sai
                                 group by sai.id,sai.device,sai.nameshow
                                ) sa
                    group by sa.id,sa.device having max(sa.flagw)=1) saw on p.id=saw.id and p.device=saw.device
              join (select da.id,da.device,concat(replace(group_concat(da.nameshow),',',';&lt;br /&gt;'),';') dstaddr from
                                (select dai.id,dai.device,dai.nameshow,max(dai.flag) flagw from
                                        (select pda1.id,pda1.device,a3.network nameshow,case when a3.from_network&lt;=#{dstAddr} and a3.to_network&gt;=#{dstAddr} then 1 else 0 end flag from policy_source_destination_addr pda1 join address a3 on pda1.address=a3.name and pda1.device=a3.device and pda1.zone=a3.zone where pda1.device=#{deviceName} and pda1.direction='destination'
                                         union
                                         select pda2.id,pda2.device,pda2.address nameshow,case when a4.from_network&lt;=#{dstAddr} and a4.to_network&gt;=#{dstAddr} then 1 else 0 end flag from policy_source_destination_addr pda2 join address_set as2 on pda2.address=as2.name and pda2.device=as2.device and pda2.zone=as2.zone
                                                                                join address a4 on as2.device=a4.device and as2.zone=a4.zone and as2.address=a4.name
                                                                                where pda2.device=#{deviceName} and pda2.direction='destination'
                                         union
                                         select pda3.id,pda3.device,pda3.address nameshow,case when a6.from_network&lt;=#{dstAddr} and a6.to_network&gt;=#{dstAddr} then 1 else 0 end flag from policy_source_destination_addr pda3 join address_set as5 on pda3.address=as5.name and pda3.device=as5.device and pda3.zone=as5.zone
                                                                                join address_set as6 on as5.device=as6.device and as5.zone=as6.zone and as5.address=as6.name
                                                                                join address a6 on as6.device=a6.device and as6.zone=a6.zone and as6.address=a6.name
                                                                                where pda3.device=#{deviceName} and pda3.direction='destination'
                                         union
                                         select pda3.id,pda3.device,pda3.address nameshow,1 flag from policy_source_destination_addr pda3 where pda3.device=#{deviceName} and pda3.direction='destination' and upper(pda3.address)='ANY'
                                         ) dai
                                 group by dai.id,dai.device,dai.nameshow
                                ) da
                    group by da.id,da.device having max(da.flagw)=1) daw on p.id=daw.id and p.device=daw.device
              join (select distinct ai.id,ai.device from                                         
                             (select pa1.id,pa1.device
                              from policy_application pa1 join application ap1 on pa1.device=ap1.device and pa1.application=ap1.name
                              where pa1.device=#{deviceName} and upper(ap1.protocol)=#{protocol} and if(instr(ap1.destination_port,'-')=0,ap1.destination_port=#{port},substr(ap1.destination_port,1,instr(ap1.destination_port,'-')-1)+0&lt;=#{port} and substr(ap1.destination_port,instr(ap1.destination_port,'-')+1)+0&gt;=#{port})
                              union
                              select pa2.id,pa2.device
                              from policy_application pa2 join application_set aps1 on pa2.application=aps1.name and pa2.device=aps1.device
                                                                 join application ap2 on aps1.application=ap2.name and aps1.device=ap2.device
                                                                 where pa2.device=#{deviceName} and upper(ap2.protocol)=#{protocol} and if(instr(ap2.destination_port,'-')=0,ap2.destination_port=#{port},substr(ap2.destination_port,1,instr(ap2.destination_port,'-')-1)+0&lt;=#{port} and substr(ap2.destination_port,instr(ap2.destination_port,'-')+1)+0&gt;=#{port})
                              union
                              select pa3.id,pa3.device
                              from policy_application pa3 join application_set aps2 on pa3.application=aps2.name and pa3.device=aps2.device
                                                                 join application_term apt1 on aps2.application=apt1.name and aps2.device=apt1.device
                                                                 where pa3.device=#{deviceName} and upper(apt1.protocol)=#{protocol} and if(instr(apt1.destination_port,'-')=0,apt1.destination_port=#{port},substr(apt1.destination_port,1,instr(apt1.destination_port,'-')-1)+0&lt;=#{port} and substr(apt1.destination_port,instr(apt1.destination_port,'-')+1)+0&gt;=#{port})
                              union
                              select pa4.id,pa4.device
                              from policy_application pa4 join application_map am4 on pa4.application=am4.name
                              where pa4.device=#{deviceName} and upper(am4.protocol)=#{protocol} and (if(am4.portvalue is null,1=1,if(length(am4.portvalue)-length(replace(am4.portvalue,'#',''))=2,SUBSTRING_INDEX(am4.portvalue, '#', 1)+0&lt;=#{port} and SUBSTRING_INDEX(SUBSTRING_INDEX(am4.portvalue, '#', -2), '#', 1)+0&gt;=#{port},SUBSTRING_INDEX(am4.portvalue, '#', 1)+0=#{port} or SUBSTRING_INDEX(SUBSTRING_INDEX(am4.portvalue, '#', -2), '#', 1)+0=#{port})))
                              ) ai
                    ) aw on p.id=aw.id and p.device=aw.device
              join (select a.id,a.device,a.protocol,concat(replace(group_concat(a.portshow),',',';&lt;br /&gt;'),';') port from
                                 (select pa5.id,pa5.device,ap3.protocol,case when substr(ap3.destination_port,1,instr(ap3.destination_port,'-')-1)=substr(ap3.destination_port,instr(ap3.destination_port,'-')+1) then substr(ap3.destination_port,1,instr(ap3.destination_port,'-')-1) else ap3.destination_port end portshow
                                  from policy_application pa5 join application ap3 on pa5.device=ap3.device and pa5.application=ap3.name
                                  where pa5.device=#{deviceName}
                                  union
                                  select pa6.id,pa6.device,ap4.protocol,case when substr(ap4.destination_port,1,instr(ap4.destination_port,'-')-1)=substr(ap4.destination_port,instr(ap4.destination_port,'-')+1) then substr(ap4.destination_port,1,instr(ap4.destination_port,'-')-1) else ap4.destination_port end portshow
                                  from policy_application pa6 join application_set aps3 on pa6.application=aps3.name and pa6.device=aps3.device
                                                                     join application ap4 on aps3.application=ap4.name and aps3.device=ap4.device
                                                                     where pa6.device=#{deviceName}
                                  union
                                  select pa7.id,pa7.device,apt2.protocol,case when substr(apt2.destination_port,1,instr(apt2.destination_port,'-')-1)=substr(apt2.destination_port,instr(apt2.destination_port,'-')+1) then substr(apt2.destination_port,1,instr(apt2.destination_port,'-')-1) else apt2.destination_port end portshow
                                  from policy_application pa7 join application_set aps4 on pa7.application=aps4.name and pa7.device=aps4.device
                                                                     join application_term apt2 on aps4.application=apt2.name and aps4.device=apt2.device
                                                                     where pa7.device=#{deviceName}                                           
                                  union
                                  select pa8.id,pa8.device,am8.protocol,case when am8.portvalue is null then '' else concat('#',am8.portvalue) end portshow
                                  from policy_application pa8 join application_map am8 on pa8.application=am8.name
                                  where pa8.device=#{deviceName}
                                  ) a
                    group by a.id,a.device,a.protocol) aw2 on p.id=aw2.id and p.device=aw2.device
              where p.device=#{deviceName} and p.status=#{status} and p.action=#{action}
              order by p.id+0
              limit ${start},${rows}

Answer 1

如果您使用MySQL，首先，我会阅读有关an execution plan is的参考文档。

您应该了解服务器在运行查询时执行的计划。在那里，您可以看到服务器是否正在使用您拥有的索引，或者您是否需要添加新索引等。例如。

您可以采取一些措施来优化查询。它可能是，例如，对结构进行非规范化或将其规范化......（这取决于查询）。如果更新不重要，则分区表等添加更多索引

首先，在查询之前使用 EXPLAIN 和 EXPLAIN EXTENDED 命令：

EXPLAIN SELECT ...
EXPLAIN EXTENDED SELECT ...

从那里，您可以看到查询引擎盖下发生的事情，并进行您认为可以改善效果的更改。

Answer 2

第一步：尝试使用视图或存储过程以使其更具可读性。

下一步：使用查询计划或自行运行每个视图/查询/存储过程并检查运行时间来检查哪个查询是语句的瓶颈

Answer 3

哇，这是一段SQL，是一个~40表连接。

鉴于其复杂性，我很难看到任何明显的方法来大幅提升性能。

使用EXPLAIN可能会有所帮助，但是使用它的子查询数量可能只是抱怨大多数（因为它不会使用加入子查询的索引 - 同样适用于视图，这可能使它更具可读性但会可能没有帮助表现，可能会阻碍它。）

有一些小的调整。对于子查询 aw ，您在主要子查询周围有一个额外的查询，它正在执行DISTINCT。由于主要子查询是4个联合查询，因此UNION语句已经消除了重复项。因此，执行DISTINCT的外部查询是多余的。

进一步说。您的主要查询是检查策略表。我认为这大大减少了要处理的记录数，但是每个子查询都返回了大量与之不匹配的行。在每个子查询中对策略执行额外连接可能会更快，以减少每个子查询返回的记录（并在可以使用索引的级别执行此操作）。

这样的事情： -

SELECT p.id,p.from_zone fromzone,p.to_zone tozone,p.action,p.status,saw.srcaddr,daw.dstaddr,aw2.protocol,CASE WHEN aw2.port=';' then ' ' else aw2.port end port                            
FROM policy p 
JOIN 
(
    SELECT sa.id,sa.device,CONCAT(REPLACE(GROUP_CONCAT(sa.nameshow),',',';&lt;br /&gt;'),';') srcaddr 
    FROM                                          
    (
        SELECT sai.id,sai.device,sai.nameshow,max(sai.flag) flagw 
        FROM
        (
            SELECT psa1.id,psa1.device,a1.network nameshow,CASE WHEN a1.from_network&lt;=#{srcAddr} AND a1.to_network&gt;=#{srcAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr psa1 ON p.id=psa1.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address a1 ON psa1.address=a1.name AND psa1.device=a1.device AND psa1.zone=a1.zone 
            WHERE psa1.device=#{deviceName} AND psa1.direction='source'
            UNION
            SELECT psa2.id,psa2.device,psa2.address nameshow,CASE WHEN a2.from_network&lt;=#{srcAddr} AND a2.to_network&gt;=#{srcAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr psa2 ON p.id=psa2.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address_set as1 ON psa2.address=as1.name AND psa2.device=as1.device AND psa2.zone=as1.zone
            JOIN address a2 ON as1.device=a2.device AND as1.zone=a2.zone AND as1.address=a2.name
            WHERE psa2.device=#{deviceName} AND psa2.direction='source'
            UNION
            SELECT psa3.id,psa3.device,psa3.address nameshow,CASE WHEN a5.from_network&lt;=#{srcAddr} AND a5.to_network&gt;=#{srcAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr psa3 ON p.id=psa3.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address_set as3 ON psa3.address=as3.name AND psa3.device=as3.device AND psa3.zone=as3.zone
            JOIN address_set as4 ON as3.device=as4.device AND as3.zone=as4.zone AND as3.address=as4.name
            JOIN address a5 ON as4.device=a5.device AND as4.zone=a5.zone AND as4.address=a5.name
            WHERE psa3.device=#{deviceName} AND psa3.direction='source'
            UNION
            SELECT psa3.id,psa3.device,psa3.address nameshow,1 flag 
            FROM policy p 
            JOIN policy_source_destination_addr psa3 ON p.id=psa3.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            WHERE psa3.device=#{deviceName} AND psa3.direction='source' AND upper(psa3.address)='ANY'
        ) sai
        GROUP BY sai.id,sai.device,sai.nameshow
    ) sa
    GROUP BY sa.id,sa.device 
    HAVING MAX(sa.flagw)=1
) saw 
ON p.id=saw.id AND p.device=saw.device
JOIN 
(
    SELECT da.id,da.device,CONCAT(REPLACE(GROUP_CONCAT(da.nameshow),',',';&lt;br /&gt;'),';') dstaddr 
    FROM
    (
        SELECT dai.id,dai.device,dai.nameshow,max(dai.flag) flagw 
        FROM
        (
            SELECT pda1.id,pda1.device,a3.network nameshow,CASE WHEN a3.from_network&lt;=#{dstAddr} AND a3.to_network&gt;=#{dstAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr pda1  ON p.id=pda1.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address a3 ON pda1.address=a3.name AND pda1.device=a3.device AND pda1.zone=a3.zone where pda1.device=#{deviceName} AND pda1.direction='destination'
            union
            SELECT pda2.id,pda2.device,pda2.address nameshow,CASE WHEN a4.from_network&lt;=#{dstAddr} AND a4.to_network&gt;=#{dstAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr pda2  ON p.id=pda2.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address_set as2 ON pda2.address=as2.name AND pda2.device=as2.device AND pda2.zone=as2.zone
            JOIN address a4 ON as2.device=a4.device AND as2.zone=a4.zone AND as2.address=a4.name
            WHERE pda2.device=#{deviceName} AND pda2.direction='destination'
            UNION
            SELECT pda3.id,pda3.device,pda3.address nameshow,CASE WHEN a6.from_network&lt;=#{dstAddr} AND a6.to_network&gt;=#{dstAddr} then 1 else 0 end flag 
            FROM policy p 
            JOIN policy_source_destination_addr pda3  ON p.id=pda3.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            JOIN address_set as5 ON pda3.address=as5.name AND pda3.device=as5.device AND pda3.zone=as5.zone
            JOIN address_set as6 ON as5.device=as6.device AND as5.zone=as6.zone AND as5.address=as6.name
            JOIN address a6 ON as6.device=a6.device AND as6.zone=a6.zone AND as6.address=a6.name
            WHERE pda3.device=#{deviceName} AND pda3.direction='destination'
            UNION
            SELECT pda3.id,pda3.device,pda3.address nameshow,1 flag 
            FROM policy p 
            JOIN policy_source_destination_addr pda3  ON p.id=pda3.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
            WHERE pda3.device=#{deviceName} AND pda3.direction='destination' AND upper(pda3.address)='ANY'
        ) dai
        GROUP BY dai.id,dai.device,dai.nameshow
    ) da
    GROUP BY da.id,da.device 
    HAVING MAX(da.flagw)=1
) daw 
ON p.id=daw.id AND p.device=daw.device
join 
(
    SELECT pa1.id,pa1.device
    FROM policy p 
    JOIN policy_application pa1  ON p.id=pa1.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
    JOIN application ap1 ON pa1.device=ap1.device AND pa1.application=ap1.name
    WHERE pa1.device=#{deviceName} AND upper(ap1.protocol)=#{protocol} AND if(INSTR(ap1.destination_port,'-')=0,ap1.destination_port=#{port},SUBSTR(ap1.destination_port,1,INSTR(ap1.destination_port,'-')-1)+0&lt;=#{port} AND SUBSTR(ap1.destination_port,INSTR(ap1.destination_port,'-')+1)+0&gt;=#{port})
    UNION
    SELECT pa2.id,pa2.device
    FROM policy p 
    JOIN policy_application pa2  ON p.id=pa2.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
    JOIN application_set aps1 ON pa2.application=aps1.name AND pa2.device=aps1.device
    JOIN application ap2 ON aps1.application=ap2.name AND aps1.device=ap2.device
    WHERE pa2.device=#{deviceName} AND upper(ap2.protocol)=#{protocol} AND if(INSTR(ap2.destination_port,'-')=0,ap2.destination_port=#{port},SUBSTR(ap2.destination_port,1,INSTR(ap2.destination_port,'-')-1)+0&lt;=#{port} AND SUBSTR(ap2.destination_port,INSTR(ap2.destination_port,'-')+1)+0&gt;=#{port})
    UNION
    SELECT pa3.id,pa3.device
    FROM policy p 
    JOIN policy_application pa3  ON p.id=pa3.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
    JOIN application_set aps2 ON pa3.application=aps2.name AND pa3.device=aps2.device
    JOIN application_term apt1 ON aps2.application=apt1.name AND aps2.device=apt1.device
    WHERE pa3.device=#{deviceName} AND upper(apt1.protocol)=#{protocol} AND if(INSTR(apt1.destination_port,'-')=0,apt1.destination_port=#{port},SUBSTR(apt1.destination_port,1,INSTR(apt1.destination_port,'-')-1)+0&lt;=#{port} AND SUBSTR(apt1.destination_port,INSTR(apt1.destination_port,'-')+1)+0&gt;=#{port})
    UNION
    SELECT pa4.id,pa4.device
    FROM policy p 
    JOIN policy_application pa4  ON p.id=pa4.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
    JOIN application_map am4 ON pa4.application=am4.name
    WHERE pa4.device=#{deviceName} AND upper(am4.protocol)=#{protocol} AND (if(am4.portvalue is null,1=1,if(length(am4.portvalue)-length(replace(am4.portvalue,'#',''))=2,SUBSTRING_INDEX(am4.portvalue, '#', 1)+0&lt;=#{port} AND SUBSTRING_INDEX(SUBSTRING_INDEX(am4.portvalue, '#', -2), '#', 1)+0&gt;=#{port},SUBSTRING_INDEX(am4.portvalue, '#', 1)+0=#{port} or SUBSTRING_INDEX(SUBSTRING_INDEX(am4.portvalue, '#', -2), '#', 1)+0=#{port})))
) aw 
ON p.id=aw.id AND p.device=aw.device
JOIN 
(
    SELECT a.id,a.device,a.protocol,CONCAT(REPLACE(GROUP_CONCAT(a.portshow),',',';&lt;br /&gt;'),';') port 
    FROM
    (
        SELECT pa5.id,pa5.device,ap3.protocol,CASE WHEN SUBSTR(ap3.destination_port,1,INSTR(ap3.destination_port,'-')-1)=SUBSTR(ap3.destination_port,INSTR(ap3.destination_port,'-')+1) then SUBSTR(ap3.destination_port,1,INSTR(ap3.destination_port,'-')-1) else ap3.destination_port end portshow
        FROM policy p 
        JOIN policy_application pa5  ON p.id=pa5.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
        JOIN application ap3 ON pa5.device=ap3.device AND pa5.application=ap3.name
        WHERE pa5.device=#{deviceName}
        UNION
        SELECT pa6.id,pa6.device,ap4.protocol,CASE WHEN SUBSTR(ap4.destination_port,1,INSTR(ap4.destination_port,'-')-1)=SUBSTR(ap4.destination_port,INSTR(ap4.destination_port,'-')+1) then SUBSTR(ap4.destination_port,1,INSTR(ap4.destination_port,'-')-1) else ap4.destination_port end portshow
        FROM policy p 
        JOIN policy_application pa6  ON p.id=pa6.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
        JOIN application_set aps3 ON pa6.application=aps3.name AND pa6.device=aps3.device
        JOIN application ap4 ON aps3.application=ap4.name AND aps3.device=ap4.device
        WHERE pa6.device=#{deviceName}
        UNION
        SELECT pa7.id,pa7.device,apt2.protocol,CASE WHEN SUBSTR(apt2.destination_port,1,INSTR(apt2.destination_port,'-')-1)=SUBSTR(apt2.destination_port,INSTR(apt2.destination_port,'-')+1) then SUBSTR(apt2.destination_port,1,INSTR(apt2.destination_port,'-')-1) else apt2.destination_port end portshow
        FROM policy p 
        JOIN policy_application pa7  ON p.id=pa7.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
        JOIN application_set aps4 ON pa7.application=aps4.name AND pa7.device=aps4.device
        JOIN application_term apt2 ON aps4.application=apt2.name AND aps4.device=apt2.device
        WHERE pa7.device=#{deviceName}                                           
        UNION
        SELECT pa8.id,pa8.device,am8.protocol,CASE WHEN am8.portvalue is null then '' else concat('#',am8.portvalue) END portshow
        FROM policy p 
        JOIN policy_application pa8  ON p.id=pa8.id AND p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
        JOIN application_map am8 ON pa8.application=am8.name
        WHERE pa8.device=#{deviceName}
    ) a
    GROUP BY a.id,a.device,a.protocol
) aw2 
ON p.id=aw2.id AND p.device=aw2.device
WHERE p.device=#{deviceName} AND p.status=#{status} AND p.action=#{action}
ORDER BY p.id+0
LIMIT ${start},${rows}

Answer 4

order by p.id+0 - id是VARCHAR持有号码。那伤害了。
JOIN ( SELECT ... ) JOIN ( SELECT ... )优化非常，因为这些子查询没有索引。重新构造整个查询，或使用添加索引的tmp表。
where pa7.device=#{deviceName} - policy_application需要INDEX(device)。好吧，如何提供SHOW CREATE TABLE，以便我们知道您已经拥有哪些索引。
where psa1.device=#{deviceName} and psa1.direction='source' - policy_source_destination_addr需要INDEX(device, direction)（按任意顺序排列）。

Answer 5

难以阅读不是因为它很长，而是因为缺乏格式化使其视觉上复杂且难以理解。

如果有的话，应该分成更多行...

select
  p.id                ,
  p.from_zone fromzone,
  p.to_zone   tozone  ,
  p.action            ,
  p.status            ,
  saw.srcaddr

旨在通过降低妨碍大脑理解其含义的视觉复杂性来使其可读......

select psa3.id              ,
       psa3.device          ,
       psa3.address nameshow,
       case when a5.from_network <=#{srcAddr} and 
                 a5.to_network   <=#{srcAddr}
            then 1
            else 0
       end flag 
from   policy                         p 
join   policy_source_destination_addr psa3 on p.id         = psa3.id       and
                                              p.device     = #{deviceName} and 
                                              p.status     = #{status}     and
                                              p.action     = #{action}
join   address_set                    as3  on psa3.address = as3.name      and
                                              psa3.device  = as3.device    and
                                              psa3.zone    = as3.zone
join   address_s ...

视觉复杂程度越低，您的大脑就越能识别代码中有意义的复杂性，例如四列连接，函数和案例语句的存在，列和表别名的存在和值等..

添加内联评论，以帮助他们...我自己的代码库中的一个例子......

with
  cte_book_list as (
    -- retrieves a list of book_id's and the batch id
    -- we do this to provide a list of book_id's that can be used in a number of
    -- other CTE's below. The batch ID is included so this table doesn't have to be
    -- referenced again.
    select
      rb.id                             batch_id,
      rb.client_id                     client_id,

行数无关紧要。我的陈述超过500行，易于阅读，理解和维护。

Answer 6

我假设您已经知道如何优化正常大小的查询，并且您只想要了解如何控制大量查询的复杂性。

最近我不得不分析和优化一些大型视图（＆gt; 30个连接）。我已经为自己创造了一些工具（仍然是草案，我不愿意在这个阶段分享），这些工具帮助我取得了良好的成绩。

可视化

我用FoundationDB Java parser分叉进行了一段时间的实验，以便我可以解析视图并创建视图结构的MindMap（FreeMind有一个简单的基于xml的格式）。这非常有用，因为在这里和那里重复了一些模式，并且在图表上识别它们很简单。

即使您没有工具，绘制图表也是一个好主意查询结构的表和子查询

（在Freemind中绘制的示例下面。带有＆＃34; list＆＃34;图标的节点是实际表格。）

分而治疗

尝试分解查询：查看自己的每个子查询，联合的每个部分。尝试获取它们的内容并进行一些实验以简化它们或优化它们。

A＆＃34;本地优化＆＃34;可能不能保证你有很大的改进，但是这个阶段对于熟悉所有的大型查询非常重要部分。

测试，测试，测试

本地方法（＆＃34; divide et impera＆＃34;）还有一个好处，就是你可以自己测试每个子查询（如果总查询真的很慢，那么测试任何回归都需要时间总查询）。如果查询的所有部分都在返回相同的行，您可以集中精力使它们更有效地协同工作。

以小型可管理的块测试您的重新设计

在更高级别管理查询

同样适用于＆＃34; divide et impera＆＃34;我发现创建我的手工工具很有用：在这种情况下，一个＆＃34;查询编译器＆＃34;。

基本上我将每个子查询复制到它自己的文件中，给它一个我能想出的最有意义的名字，并使用一个库来导入主查询中的子查询源（我使用Freemarker）

我们的目标是拥有更多的“manegeable”＆＃34; SQL之后，有了优化子查询，你可以分析和优化如何子查询正在一起工作。

或者，您可以通过为子查询创建视图来实现相同的结果，以便简化高级查询（我没有这种可能性）。

如何优化长SQL语句？

6 个答案: