UPDATE categories FROM categories c JOIN categories_translations 浏览9提问于2022-06-22得票数 1 1回答 带有PostgreSQL的Rails 3:联接表中的“update_all”问题 、、、 在Rails 3中,我试图使用像self.children.joins(:parent).where(...).update_all(...)这样的语句来选择记录的子集并更新它们。所讨论的语...
UPDATE product p SET net_price = price - price * discount FROM product_segment s WHERE p.segment_id = s.id; This statement joins the product table to the product_segment table. If there is a match in both tables, it gets a discount from the product_segment table, calculates the net ...
15.索引并不是越多越好,索引固然可以提高相应的 select 的效率,但同时也降低了 insert 及 update 的效率,因为 insert 或 update 时有可能会重建索引,所以怎样建索引需要慎重考虑,视具体情况而定。一个表的索引数最好不要超过6个,若太多则应考虑一些不常使用到的列上建的索引是否有必要。 16.应尽可能的避免更...
Joins –show you a brief overview of joins in PostgreSQL. Table aliases –describes how to use table aliases in the query. Inner Join–select rows from one table that have the corresponding rows in other tables. Left Join – select rows from one table that may or may not have the corr...
UPDATE JOINS We can use UPDATE JOINS to add values from a separate table. In the below example, we have updated the values in the second table by joining the values from the first table specifying the condition in the WHERE clause.
test=#DROPINDEX immv_index;DROPINDEXtest=#UPDATEpgbench_accountsSETabalance=9876WHEREaid=1;UPDATE1Time:3224.741ms(00:03.225) 七、支持的视图定义和限制 目前,IMMV的视图定义可包含inner joins、DISTINCT子句、一些内建的聚合函数、 在FROM子句中的简单子查询、简单的 CTE (WITH查询)。支持包括自联接在内的内...
PostgreSQL传统的分区方法,使用约束来区分不同分区存放的数据(配置constraint_exclusion=partition),执行select/delete/update时执行计划根据约束和查询条件排除不需要查询的分区表。 调用COPY或插入数据时使用触发器或规则,将数据插入对应的分区表。 传统的做法,无论是查询还是插入,对性能的影响都较大。 pg_pathman与传统...
不堵塞DML Non-blocking concurrent table partitioning; partition_table_concurrently(relation REGCLASS, batch_size INTEGER DEFAULT 1000, sleep_time FLOAT8 DEFAULT 1.0) 分区表执行计划自动根据分区定义进行优化 Effective query planning for partitioned tables (JOINs, subselects etc); 分区表支持外部数据源 FDW...
The NATURAL LEFT JOIN joins a row from b where all columns of the same name hold same values. We don't need an update in this case (nothing changes) and can eliminate those rows early in the process (WHERE b.id IS NULL).We still need to find a matching row, so b.id = ab.id...
we have to join in the order shown by the joins. In that case, the join tree shows the structure of the JOIN expressions. The restrictions associated with particular JOIN clauses (from ON or USING expressions) are stored as qualification expressions attached to those join-tree nodes. It turn...