从MySQL 5.7.5开始,默认SQL mode模式包括 ONLY_FULL_GROUP_BY。(在5.7.5之前,MySQL不检测功能依赖性,ONLY_FULL_GROUP_BY默认情况下不启用。 6、HAVING :对VT5应用HAVING筛选器,只有为true的组插入到VT6。 HAVING同GROUP BY一样,MySQL拓展SQL标准以允许HAVING可以使用别名和非列表表达式。 7、SELECT:将VT6每一...
监控索引级别的膨胀: https://github.com/ioguix/pgsql-bloat-estimation/blob/master/btree/btree_bloat.sql -- WARNING: executed with a non-superuser role, the query inspect only index on tables you are granted to read. -- WARNING: rows with is_na = 't' are known to have bad statistics ...
Group Key:customer.c_custkey->Nested Loop Left Join->Parallel Index Only Scan using customer_pkey on customer->Index Scan using idx_orders_custkey on orders Index Cond:(customer.c_custkey=o_custkey)Filter:((o_comment)::text!~~'%special%deposits%'::text)...
->Index Only Scanusingt1_a1_keyont1(cost=0.28..45.09rows=952width=4) Index Cond: (a1 IS NOT NULL) group by优化 如果不对group by优化,那么将会需要对结果进行Sort或者Hash,但是如果表中数据已经是排序好的,那么将可以对其进行优化。 create index tt1_id_keyontt1usingbtree(id); postgres=> explain...
Gather发生在最后阶段,因此“Nested Loop Left Join”是并行操作。“Parallel Index Only Scan”在版本10才可以使用,和并行顺序扫描类似。c_custkey = o_custkey条件读取每个customer行的order列,因此不是并行。 8、Hash Join PgSQL11中每个worker构建自己的hash table。因此,4+ workers不能提升性能。新的实现方式...
SELECTname, altitudeFROMONLYcitiesWHEREaltitude>500; name|altitude---+---Las Vegas|2174Mariposa|1953(2rows) 标签:postgreSql 好文要顶关注我收藏该文微信分享 香草味的薄荷糖 粉丝-0关注 -15 +加关注 0 0 升级成为会员 «上一篇:数据库题目总结...
I am trying to authenticate a 3rd-party tool over Azure database for PostgreSQL - Flexible server using Entra ID only. so I created multiple service principals (access-token based, password-based auth and Certificate-based auth). The access token one,…
ALTER SEQUENCE 名字 [ INCREMENT [ BY ] 递增 ] [ MINVALUE 最小值 | NO MINVALUE ] [ MAXVALUE 最大值 | NO MAXVALUE ] [ RESTART [ WITH ] 开始 ] [ CACHE 缓存 ] [ [ NO ] CYCLE ] 命令: ALTER TABLE 描述: 改变一个表的定义 语法: ALTER TABLE [ ONLY ] 表名 [ * ] action [, ...
UPDATE [ ONLY ] table SET column = { expression | DEFAULT } [, ...] [ FROM from_list ] [ WHERE condition ]VACUUM垃圾收集以及可选地分析一个数据库。VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ] VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...]...
full_page_writes = off # recover from partial page writes , 生产中,如果有增量备份和归档,可以关闭,提高性能。 wal_buffers = 1GB # min 32kB, -1 sets based on shared_buffers ,wal buffer大小,如果大量写wal buffer等待,则可以加大。 wal_writer_delay = 10ms # 1-10000 milliseconds wal buffer调...