Every movie needs a director and every rented movie needs to exist in the store. How do we make sure something in another table exists before inserting new data? This lesson will teach us about foreign keys and references. CREATETABLEdirectors ( id SERIALPRIMARYKEY, nameVARCHAR(100)UNIQUENOTNU...
Learn the basics of Postgres table creation, with primary keys, foreign keys, and data types. Row Level Security Learn how to use Postgres’ Row Level Security functionality. It’s a great tool for managing key-based partitioning in a multi-tenant world. Partitioning Learn how to create partit...
✅ 最佳回答: \i tmp.sql -- Create some data to test it on CREATE TABLE events (id integer PRIMARY KEY); INSERT INTO events(id) VALUES(221), (222); CREATE TABLE matches ( id text , event_id text , fighter_a_id text , fighter_b_id text ); INSERT INTO matches(id, event_id...
CREATETABLEorders ( order_id SERIALPRIMARYKEY, order_dateDATENOTNULL, customer_idINTNOTNULL); 在此示例中,order_id是主键,它确保每个订单都有一个唯一标识符,并且不允许为空。 2.4 FOREIGN KEY 约束 FOREIGN KEY约束用于建立表与表之间的关系。它确保表中的某个列的值必须存在于另一个表的主键或唯一键列...
PRIMARY KEY 约束 FOREIGN KEY 约束 CHECK 约束 EXCLUSION 约束 2.1 NOT NULL 约束 NOT NULL约束用于确保某个列不能包含空值(NULL)。当某个列被定义为NOT NULL时,任何插入或更新操作都必须为该列提供一个非空值。 示例: CREATETABLEemployees(employee_idSERIALPRIMARYKEY,first_nameVARCHAR(50)NOTNULL,last_nameVA...
CREATE TABLE test003 ( ID int identity(1,1) primary key, test002ID int foreign key references test002(ID),--创建外键 OrderDate datetime default(getdate()), name nvarchar(20) not null ) GO exec sp_helpconstraint test003 --查询到系统默认生成FK__test003__test002__023D5A04名称外键 ...
create table authorities (username varchar(50) not null,authority varchar(50) not null,constraint fk_authorities_users foreign key(username) references users(username)); create unique index ix_auth_username on authorities (username,authority); ...
1.修改表结构删除列的命令是ALTERTABLE ___ DROP COLUMN column_name; 2.提取JSON字段"name":"Alice"中的name值应使用操作符___ 3.创建存储过程时,返回VOID类型的语法是CREATE___ func_name() ... 4.查询当前日期函数是___ 5.使用正则表达式匹配以A开头的字符串需写为___’A%’ 6.创建表空间指定路...
数据库配置错误:Postgres的配置文件中有一些参数可以影响级联删除的行为,例如foreign_key_constraints和referential_integrity。如果这些参数被设置为禁用级联删除,那么级联删除将不起作用。可以通过检查和修改这些参数来解决此问题。 子表中的数据不一致:如果子表中的数据与主表的外键约束不一致,那么级联删除将无法生效。可...
FOREIGN KEY (manager_id) REFERENCES employees(employee_id) ) ;除了自定义表的结构之外,PostgreSQL 还提供了另一个创建表的方法,就是通过一个查询的结果创建新表:CREATE TABLE [ IF NOT EXISTS ] table_nameAS query[ WITH [ NO ] DATA ];例如,我们可以基于 employees 复制出一个新的表:CREATE...