LIMIT 1 的优化效果:当查询仅需返回一条记录时,优化器可能选择直接遍历主键索引(从最大id开始),逐行检查WHERE条件,直到找到第一条匹配的记录,避免全表扫描。 3.prefer_ordering_index禁用后的影响 关闭后的行为变化:禁用prefer_ordering_index后,优化器不再强制优先选择排序索引,但主键索引的聚簇特性仍使其成为最有...
LIMIT 1 的优化效果:当查询仅需返回一条记录时,优化器可能选择直接遍历主键索引(从最大id开始),逐行检查WHERE条件,直到找到第一条匹配的记录,避免全表扫描。 3.prefer_ordering_index禁用后的影响 关闭后的行为变化:禁用prefer_ordering_index后,优化器不再强制优先选择排序索引,但主键索引的聚簇特性仍使其成为最有...
LIMIT 1 的优化效果:当查询仅需返回一条记录时,优化器可能选择直接遍历主键索引(从最大id开始),逐行检查WHERE条件,直到找到第一条匹配的记录,避免全表扫描。 3.prefer_ordering_index禁用后的影响 关闭后的行为变化:禁用prefer_ordering_index后,优化器不再强制优先选择排序索引,但主键索引的聚簇特性仍使其成为最有...
LIMIT 1 的优化效果:当查询仅需返回一条记录时,优化器可能选择直接遍历主键索引(从最大id开始),逐行检查WHERE条件,直到找到第一条匹配的记录,避免全表扫描。 3.prefer_ordering_index禁用后的影响 关闭后的行为变化:禁用prefer_ordering_index后,优化器不再强制优先选择排序索引,但主键索引的聚簇特性仍使其成为最有...
mysql> set optimizer_switch = "prefer_ordering_index=off"; Query OK, 0 rows affected (0.00 sec) mysql> select * from t_user where age >= 20 and age < 50 order by id limit 10; 1. 2. 3. 这里明显的结果是打开这个参数后,运行的结果会很快给出,但是关闭后,性能会较低。
关闭后的行为变化:禁用prefer_ordering_index后,优化器不再强制优先选择排序索引,但主键索引的聚簇特性仍使其成为最有效的访问路径。此时,优化器可能基于以下逻辑决策: 成本估算:全表扫描主键索引的成本可能低于其他索引(如k索引)的随机访问。 天然有序性:主键索引本身已按id排序,直接利用其顺序可避免Using filesort。
7. Preference assessment 8. Preference criterion 9. Preference claim 10. Preference demand 11. Preference criterion 12. Preference curve 13. Preference maximisation 14. Preference ordering 15. Preference distribution 16. Preference structure 17. Preference system 18. Preference set 19. Preference value ...
research firmDynatahave released the results of a market survey of more than 1,000 U.S.-based diners who have ordered food from a quick service/fast-food chain, fast-casual chain, or casual dining chain within the previous three months about their ordering ha...
Following consent, participants were asked to complete a short online demographic questionnaire which captured their gender, age, ethnicity, religion, highest educational attainment of parents, and full postcode which allowed the researchers to identify the Multiple Index of Deprivation centiles for the ...
Website:http://mookata.com/en/index.php?id_cms=8&controller=cms&id_lang=1 Home-cooked Basil Pesto Sauce During one orchestra rehearsal, a chorister made pesto sauce and spread it over cream crackers as a break-snack. It was so good I couldn’t forget the taste and had an urge to ma...