PostgreSQL - SELECT DatabasePrevious Quiz Next This chapter explains various methods of accessing the database. Assume that we have already created a database in our previous chapter. You can select the database using either of the following methods −Database SQL Prompt OS Command Prompt...
select * from info where (name = '李杰' or email="pyyu@live.com") and age=49; select * from info where id in (1,4,6); select * from info where id not in (1,4,6); select * from info where id in (select id from depart); # select * from info where id in (1,2,3);...
本文将深入探讨 PostgreSQL 中最核心的 SQL 操作——SELECT 查询与数据过滤,通过40+ 个真实业务场景案例,全面解析WHERE子句、运算符(BETWEEN/IN/LIKE)及复杂条件组合的用法。所有示例均基于模拟的电商数据库,包含 5 张业务表结构设计。 一、环境准备与测试数据 1.1 创建示例数据库 -- 创建电商数据库CREATEDATABASEe...
1、查询执行数据库大小 select pg_size_pretty (pg_database_size('db_product')); 2、查询数据库实例当中各个数据库大小 select datname, pg_size_pretty (pg_database_size(datname)) AS size from pg_database; 3、查询单表数据大小 select pg_size_pretty(pg_relation_size('product')) as size; 4...
PostgreSQL INSERT INTO 语句用于向表中插入新记录。 我们可以插入一行也可以同时插入多行。 INSERTINTOTABLE_NAME (column1, column2, column3,...columnN)VALUES(value1, value2, value3,...valueN); column1, column2,...columnN 为表中字段名。
The following Python program connects to a database named mydb of PostgreSQL and retrieves all the records from a table named EMPLOYEE.import psycopg2 #establishing the connection conn = psycopg2.connect( database="mydb", user='postgres', password='password', host='127.0.0.1', port= '5432'...
我用的是Postgresql9.4,但感觉mysql应该也差不多,首先创建一个简单表,只有简单的3列,在这个问题的下面好多人提到了需要看表的大小,其实这个问题和表大小无关,只和index的大小有关,因为是index是建立在int上的,所以只和纪录数目有关。 Table"public.t9"Column|Type|Modifiers---+---+---c1|integer|c2|charact...
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Summary: in this tutorial, you will learn how to use the PostgreSQL SELECT INTO statement to create a new table from the result set of a query. If you want to select data into variables, check out the PL/pgSQL SELECT INTO statement. Introduction to PostgreSQL SELECT INTO statement The Pos...
SELECT DISTINCT s.* FROM ( SELECT code, title, country FROM data_a GROUP BY code, title, country, sortorder ORDER BY sortorder ) s; Any suggestions for how to do this? postgresql Share Improve this question Follow asked Apr 8, 2020 at 22:31 cheslijones 3...