SELECT comb_id, comb_name FROM cc_company_branch GROUP BY comb_name;这条语句应该怎么优化？

对于这条查询语句，可以考虑以下几种优化方法：

1. 添加索引：可以在 cc_company_branch 表的 comb_name 列上添加索引，以提高查询性能。这样 MySQL 优化器在执行查询时就可以使用索引加速查询。

2. 改变 GROUP BY 顺序：可以将 GROUP BY comb_name 改为 GROUP BY comb_id。这样 MySQL 优化器在执行查询时就可以直接使用索引进行分组，而不需要进行额外的排序操作，从而提高查询性能。

3. 使用子查询：可以使用子查询来代替 GROUP BY，例如：

   SELECT comb_id, comb_name FROM cc_company_branch WHERE comb_name IN (SELECT comb_name FROM cc_company_branch GROUP BY comb_name);

这样 MySQL 优化器就可以先执行子查询，获取到所有的 comb_name，然后再根据这些 comb_name 查询对应的 comb_id 和 comb_name，从而避免了 GROUP BY 操作，提高查询性能。

需要根据具体情况选择优化方法，综合考虑数据表结构、查询频率等因素。同时，需要注意优化的效果和对系统性能的影响，避免过度优化。

相关问题

SELECT c.*, cu.person_name, comb.comb_name, comp.comp_name, org.org_name sys_org_name, org2.org_name sys_org2_name, gcount FROM cc_bank_card c LEFT JOIN cc_client_user_detail cu ON c.open_user_id = cu.user_id LEFT JOIN cc_company_branch comb ON comb.comb_id = c.comb_id LEFT JOIN cc_company comp ON comp.comp_id = c.comp_id LEFT JOIN sys_org org ON org.org_id = c.sys_org_id LEFT JOIN sys_org org2 ON org2.org_id = c.sys_org2_id INNER JOIN (SELECT id_card, count(card_id) gcount FROM cc_bank_card i WHERE i.delete_flag = 'NOT_DELETE' GROUP BY id_card HAVING count(card_id) >= 2) g ON g.id_card = c.id_card WHERE c.delete_flag = 'NOT_DELETE' ORDER BY gcount DESC, id_card, create_time DESC 这条sql你会怎么去优化

这条 SQL 语句的主要问题在于它包含了多个 JOIN 操作，而且其中包含了子查询，这可能导致性能瓶颈。为了优化这条 SQL 语句，可以考虑以下几个方面：

1. 尽量避免使用子查询，可以将子查询中的逻辑转换为 JOIN 操作或者使用临时表。

2. 对于 LEFT JOIN 操作，可以考虑将其转换为 INNER JOIN 操作，这样可以减少 JOIN 操作的数量，从而提高查询性能。

3. 尽量减少 SELECT 语句中 SELECT 字段的数量，只选择必要的字段，这样可以减少数据传输的开销。

4. 优化 WHERE 子句中的条件，可以考虑使用索引来加速查询。

5. 对于 ORDER BY 子句中的排序操作，可以考虑对排序字段建立索引，从而提高查询性能。

具体的优化策略需要根据具体的数据情况和业务需求来定制，以上仅供参考。

帮我优化如下sql：SELECT T1.quyu, T2.lastNum, T3.jdNum, T4.xcNum FROM (SELECT STREET AS quyu FROM STREET_YXW WHERE 1=1 GROUP BY STREET ) T1 LEFT JOIN ( SELECT T2.STREET_NAME AS quyu,COUNT(*) AS lastNum FROM V_FIRESAFETYREGISTER_DYC T1 LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T2 ON LEFT(T1.HOUSEID,19) = T2.BUILDING_CODE WHERE T1.LASTLOGOUTTIME IS NOT NULL and date_format(T1.LASTLOGOUTTIME,'%Y') = ? GROUP BY T2.STREET_NAME ) T2 ON T1.quyu = T2.quyu LEFT JOIN ( SELECT T3.STREET_NAME AS quyu,COUNT(DISTINCT T1.FIREID) AS jdNum FROM V_SX_FIRESAFETYPLAN T1 LEFT JOIN V_FIRESAFETYREGISTER_DYC T2 ON T1.FIREID = T2.ID LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T3 ON LEFT(T2.HOUSEID,19) = T3.BUILDING_CODE WHERE T1.DATE_NEW IS NOT NULL and date_format(T1.DATE_NEW,'%Y') = ? GROUP BY T3.STREET_NAME ) T3 ON T1.quyu = T3.quyu LEFT JOIN ( SELECT T3.STREET_NAME AS quyu,COUNT(*) as xcNum FROM V_SX_FIRESAFETYTRAINING T1 LEFT JOIN V_FIRESAFETYREGISTER_DYC T2 ON T1.FIREID = T2.ID LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T3 ON LEFT(T2.HOUSEID,19) = T3.BUILDING_CODE WHERE T1.TRAININGTIME IS NOT NULL and date_format(T1.TRAININGTIME,'%Y') = ? GROUP BY T3.STREET_NAME ) T4 ON T1.quyu = T4.quyu ORDER BY T2.lastNum limit ?,?

可以尝试以下优化：

1. 对于子查询中的表，添加合适的索引以提高查询效率；

2. 可以考虑将子查询改为临时表，避免多次重复查询；

3. 在需要排序的字段上添加索引；

4. 尽量避免在 JOIN 条件中使用函数，可以将日期比较条件提取到 WHERE 子句中。

优化后的 SQL 如下：

CREATE TEMPORARY TABLE tmp_street AS
SELECT STREET AS quyu FROM STREET_YXW WHERE 1=1 GROUP BY STREET;

CREATE TEMPORARY TABLE tmp_lastNum AS
SELECT T2.STREET_NAME AS quyu, COUNT(*) AS lastNum
FROM V_FIRESAFETYREGISTER_DYC T1
LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T2 ON LEFT(T1.HOUSEID, 19) = T2.BUILDING_CODE
WHERE T1.LASTLOGOUTTIME IS NOT NULL AND date_format(T1.LASTLOGOUTTIME,'%Y') = ?
GROUP BY T2.STREET_NAME;

CREATE TEMPORARY TABLE tmp_jdNum AS
SELECT T3.STREET_NAME AS quyu, COUNT(DISTINCT T1.FIREID) AS jdNum
FROM V_SX_FIRESAFETYPLAN T1
LEFT JOIN V_FIRESAFETYREGISTER_DYC T2 ON T1.FIREID = T2.ID
LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T3 ON LEFT(T2.HOUSEID, 19) = T3.BUILDING_CODE
WHERE T1.DATE_NEW IS NOT NULL AND date_format(T1.DATE_NEW,'%Y') = ?
GROUP BY T3.STREET_NAME;

CREATE TEMPORARY TABLE tmp_xcNum AS
SELECT T3.STREET_NAME AS quyu, COUNT(*) AS xcNum
FROM V_SX_FIRESAFETYTRAINING T1
LEFT JOIN V_FIRESAFETYREGISTER_DYC T2 ON T1.FIREID = T2.ID
LEFT JOIN V_HSE_COMB_BUILDING_INFO_PA T3 ON LEFT(T2.HOUSEID, 19) = T3.BUILDING_CODE
WHERE T1.TRAININGTIME IS NOT NULL AND date_format(T1.TRAININGTIME,'%Y') = ?
GROUP BY T3.STREET_NAME;

SELECT T1.quyu, T2.lastNum, T3.jdNum, T4.xcNum
FROM tmp_street T1
LEFT JOIN tmp_lastNum T2 ON T1.quyu = T2.quyu
LEFT JOIN tmp_jdNum T3 ON T1.quyu = T3.quyu
LEFT JOIN tmp_xcNum T4 ON T1.quyu = T4.quyu
ORDER BY T2.lastNum
LIMIT ?,?;

请注意，这只是一种可能的优化方案，具体的优化方法还要根据数据库的实际情况进行调整。