在PostgreSQL 中,DISTINCT 关键字与 SELECT 语句一起使用,用于去除重复记录,只获取唯一的记录。 我们平时在操作数据时,有可能出现一种情况,在一个表中有多个重复的记录,当提取这样的记录时,DISTINCT 关键字就显得特别有意义,它只获取唯一一次记录,而不是获取重复记录。 语法 用于去除重复记录的 DISTINCT 关键字的基本...
PRIMARY KEY:The primary key identifies a record from the table uniquely. A PostgreSQL table can have only one primary key. You can include multiple columns in one primary key FOREIGN KEY:A foreign key establishes a Parent-child relationship between the tables of the PostgreSQL database. A forei...
其次是约束,我们可以看到上面的DDL语句中出现了三种约束,分别是:主键(Primary Key)约束、外键(Foreign Key)约束以及非空(Not Null)约束,很显然,表复制的同时这三种约束都应存在,中间的语句还有若干条comment(注释),理论上注释内容在表复制的同时也应该存在,所以简单总结一下我们做表复制的取舍: 所有约束、索引和注释...
NULL, Primary key, foreign key, check constraints. The following creates a new person table in PostgreSQL database using psql. Example: Create a New Table Copy CREATE TABLE IF NOT EXISTS person ( Id INT PRIMARY KEY, first_name VARCHAR(50) NOT NULL, last_name VARCHAR(50) NOT NULL, ...
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。
PostgreSQL Oracle MS SQL Server Operators: CREATE TABLE FOREIGN KEY ALTER TABLE ADD CONSTRAINT ADD FOREIGN KEY Problem You want to create a foreign key for a table in a database. Example We would like to create a table namedstudentthat contains a foreign key that refers to theidcolumn in ...
For more details on Foreign Key Constraints, please visit -http://dev.mysql.com/doc/refman/5.1/en/innodb-foreign-key-constraints.html PostgreSQL If you receive PostgreSQL Error likesERROR: there is no unique constraint matching given keys for referenced table "xxxx", it is caused by failure ...
搞清楚这些问题后接下来看看PostgreSQL的相关支持能为我们实现什么,首先看一下CREATE TABLE AS,官方是这样描述的: 如上图所示,CREATE TABLE AS主要做两件事情,分别是建表(CREATE DATA)和填充数据(FILL DATA),下面我们就通过CREATE TABLE AS复制一张表试试看。本篇blog的示例都会用t_key_event_file_student这张表...
In PostgreSQL, the “CREATE” command can be executed with the “VIEW” keyword tocreate a view, as demonstrated in the following syntax: CREATEVIEWname_of_viewASselect_query; Here, -“CREATE VIEW” is a command that creates a new virtual table. ...
Second, define a new function calledcreate_tables()in thecreate_tables.pymodule: importpsycopg2fromconfigimportload_configdefcreate_tables():""" Create tables in the PostgreSQL database"""commands=("""CREATE TABLE vendors (vendor_id SERIAL PRIMARY KEY,vendor_name VARCHAR(255) NOT NULL)""","...