postgresql

API 分页探讨：offset 来分页真的有效率？

由 浪尽此生 提交于 2021-01-25 13:46:55
对于设计和实现 API 来说，当结果集包含成千上万条记录时，返回一个查询的所有结果可能是一个挑战，它给服务器、客户端和网络带来了不必要的压力，于是就有了分页的功能。 通常我们通过一个 offset 偏移量或者页码来进行分页，然后通过 API 实现类似请求： GET /api/products? page =10 { "items" : [ .. .100 products]} 如果要继续访问后续数据，则修改分页参数即可。 GET /api/products? page =11 { "items" : [ .. .another 100 products]} 在使用 offset 的情况下，通常使用 ?offset=1000 和 ?offset=1100 这种大家都熟悉的方法。它要么直接调用 OFFSET 1000 LIMIT 100 的 SQL 查询数据库，要么使用 LIMIT 乘以 page 作为查询参数。 无论如何， 「这是一个次优的解决方案」 ，因为无论哪种数据库都要跳过前面 offset 指定的 1000 行。而跳过额外的offset，不管是 PostgreSQL，ElasticSearch还是 MongoDB 都存在额外开销，数据库需要对它们进行排序，计数，然后将前面不用的数据扔掉。 这是一种低效的方法，但由于它使用简单，所以大家重复地用这个方法，也就是直接把 API

Test column for special characters or only characters / numbers

由 ♀尐吖头ヾ 提交于 2021-01-24 14:10:31
问题 I tried finding special characters using generic regex attributes and NOT LIKE clause but have been getting confusing results. The research suggested that it does not work the way it works in SQL Server or elsewhere. For finding if there is any character For finding if there is any number For finding if there is any special character like '%[^0-9]%' or '%[^a-Z]%' does not work very well when finding if non-numeric data is available and if non-alphabetical data is present, respectively SELECT

Test column for special characters or only characters / numbers

由 走远了吗. 提交于 2021-01-24 14:09:10
问题 I tried finding special characters using generic regex attributes and NOT LIKE clause but have been getting confusing results. The research suggested that it does not work the way it works in SQL Server or elsewhere. For finding if there is any character For finding if there is any number For finding if there is any special character like '%[^0-9]%' or '%[^a-Z]%' does not work very well when finding if non-numeric data is available and if non-alphabetical data is present, respectively SELECT

Test column for special characters or only characters / numbers

由 假如想象 提交于 2021-01-24 14:01:29
问题 I tried finding special characters using generic regex attributes and NOT LIKE clause but have been getting confusing results. The research suggested that it does not work the way it works in SQL Server or elsewhere. For finding if there is any character For finding if there is any number For finding if there is any special character like '%[^0-9]%' or '%[^a-Z]%' does not work very well when finding if non-numeric data is available and if non-alphabetical data is present, respectively SELECT

Postgresql connectors using VC++

由 ☆樱花仙子☆ 提交于 2021-01-24 11:19:54
问题 How to add Libpqxx library in visual c++ .I googled it from past 2 days not able to get solution for the same I have downloaded and added libpqxx-4.0 but not able to add in visual studio can any give proper solution for this. Thanks in advance 回答1: As it’s my first contribution I will take the time to answer this regardless of the limited information provided by Raveendra konda. Maybe it will be of assistance to someone new to libpqxx. At the time of writing we are on libpqxx 7.0.7. I will

.NET5WTM(ASP.NET Core) PGSql开箱操作

由 佐手、 提交于 2021-01-24 10:33:54
本人WTM忠实粉丝一枚，1月份WTM终于千呼万唤始出来，本来一个开箱操作没啥好写的，但是由于本人今年工作需求，数据库由过去一直使用的sqlserver向pgsql转变。以后日子里，开发时候pgsql使用会逐渐多起来，当然sqlserver我是不会放弃的。以后wtm+pgsql的踩坑博客多逐渐多起来，大家一起成长。今天就来一个pgsql开箱的博客。 一、到WTM官网生成并下载一个项目并配置使用pgsql 这是使用WTM的.neter都会的。我们不做任何操作，直接生成并下载。解压生成的项目，并打开appsettings.json修改Connections的Value和DBType，指定我们使用的数据库为PgSql。pgsql安装完成之后默认的用户名是postgres，密码时安装时你自己设定的。详细的设置如下： "Connections": [ { "Key": "default", "Value": "User ID=postgres;Password=123456;Host=localhost;Database=PGSqlTest_DB;Pooling=true;", "DbContext": "DataContext", "DBType": "PgSql" //DataBase, you can choose mysql,sqlserver,pgsql,sqlite,oracle

How do I get the k nearest neighbors for geodjango?

由 老子叫甜甜 提交于 2021-01-24 09:21:31
问题 Assume that I have the following model: class Person: id = models.BigAutoField(primary_key=True) name = models.CharField(max_length=150) location = models.PointField() How would I go by obtaining the k nearest neighbors (KNN) by location using geodjango? Would I have to write custom SQL for that? I am using PostgreSQL with PostGIS. 回答1: You can use a raw() sql query to utilize postgis order_by operators: <-> which gets the nearest neighbor using the centers of the bounding boxes to calculate

How do I get the k nearest neighbors for geodjango?

由 别等时光非礼了梦想. 提交于 2021-01-24 09:20:40
问题 Assume that I have the following model: class Person: id = models.BigAutoField(primary_key=True) name = models.CharField(max_length=150) location = models.PointField() How would I go by obtaining the k nearest neighbors (KNN) by location using geodjango? Would I have to write custom SQL for that? I am using PostgreSQL with PostGIS. 回答1: You can use a raw() sql query to utilize postgis order_by operators: <-> which gets the nearest neighbor using the centers of the bounding boxes to calculate

How do I get the k nearest neighbors for geodjango?

由 自古美人都是妖i 提交于 2021-01-24 09:18:51
问题 Assume that I have the following model: class Person: id = models.BigAutoField(primary_key=True) name = models.CharField(max_length=150) location = models.PointField() How would I go by obtaining the k nearest neighbors (KNN) by location using geodjango? Would I have to write custom SQL for that? I am using PostgreSQL with PostGIS. 回答1: You can use a raw() sql query to utilize postgis order_by operators: <-> which gets the nearest neighbor using the centers of the bounding boxes to calculate

How to Capture error records using JDBCTemplate batchUpdate in postgreSql?

由 帅比萌擦擦* 提交于 2021-01-24 07:22:46
问题 I am using Spring JDBCTemplate and BatchPreparedStatementSetter to perform batch Update on a postgreSql DB. I wanted to capture the erroneous records and after going through some posts, found out that catching the BatchUpdateException and then looking for 'Statement.EXECUTE_FAILED' could help me identify the records that were erroneous. However, when I implement it as below, I never get a batchUpdate exception. Here I am trying to enter the same id "120" repeatedly so that I get a unique
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