2.在表创建好之后添加外键约束 alter table student add constraints pk_student_id PRIMARY key(id); 3.在创建表的语句的最后面使用 constraints pk_表名_字段名 primary key(字段名) 4.删除主键约束alter table student drop constraints pk_student_id; 验证流程: 1-1.创建一张表,在id后加上主键约束 prima...
CREATE TABLE COMPANY6( ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL ); 下面实例创建一张 DEPARTMENT1 表,并添加 3 个字段,EMP_ID 就是外键,参照 COMPANY6 的 ID: CREATE TABLE DEPARTMENT1( ID INT PRIMARY KEY NOT NULL, DEPT CHAR(50) ...
ALTER TABLE 表名 ADD CONSTRAINT 约束名 UNIQUE (字段名); 示例: ALTER TABLE students ADD CONSTRAINT unique_email UNIQUE (email); (2)删除唯一约束: 首先需要知道唯一约束的名称,可以通过以下命令查询: SELECT constraint_name FROM information_schema.table_constraints WHERE table_name = '表名' AND constra...
SELECT tc.constraint_name, tc.table_name, kcu.column_name, ccu.table_name AS foreign_table_name, ccu.column_name AS foreign_column_name, tc.is_deferrable,tc.initially_deferred FROM information_schema.table_constraints AS tc JOIN information_schema.key_column_usage AS kcu ON tc.constraint_nam...
tc.constraint_name, tc.table_name, kcu.column_name, ccu.table_name AS foreign_table_name, ccu.column_name AS foreign_column_name, tc.is_deferrable,tc.initially_deferred FROM information_schema.table_constraints AS tc JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = ...
selectkcu.table_schema, kcu.table_name, tco.constraint_name, kcu.ordinal_positionasposition, kcu.column_nameaskey_columnfrominformation_schema.table_constraints tcojoininformation_schema.key_column_usage kcuonkcu.constraint_name=tco.constraint_nameandkcu.constraint_schema=tco.constraint_schemaandkcu...
"products_pkey"PRIMARYKEY, btree (product_no)Checkconstraints: "products_price_min"CHECK(price>0::numeric) 删除字段的默认值相当于将它设置为空值(NULL)。 修改字段数据类型 通常来说,可以将字段的数据类型修改为兼容的类型。 ALTERTABLEtable_nameALTERCOLUMNcolumn_name TYPE new_data_type; ...
在PostgreSQL 中,使用CREATE TABLE语句创建一个新表: CREATETABLEtable_name(column_namedata_typecolumn_constraint,column_namedata_type,...,table_constraint); 该语句包含以下内容: 首先,table_name指定了新表的名称。 括号内是字段的定义,column_name是字段的名称,data_type是它的类型,column_constraint是可选的...
tablename, indexname, indexdef FROM pg_indexes WHERE schemaname = 'public' ORDER BY tablename, indexname; 6 系统中指定表建立的约束 SELECT constraint_name, constraint_type FROM information_schema.table_constraints WHERE table_name = '表名'; ...
{ FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ] [ FOR { UPDATE | NO KEY UPDATE | SHARE | KEY SHARE } [ OF table_name [, ...] ] [ NOWAIT | SKIP LOCKED ] [...] ] from_item 可以是以下选项之一: [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [,...