mysql> insert into t_tudent values(112,'爱国的吴京',6); ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`test_wl`.`t_tudent`, CONSTRAINT `t_tudent_ibfk_1` FOREIGN KEY (`t_class`) REFERENCES `t_class` (`class_num`)) 1. 2. 3. 4. 5...
We will use the ALTER TABLE command to remove the NOT NULL constraint from the "last_name" column: ALTERTABLEstudent_informationALTERCOLUMNlast_nameDROPNOTNULL; The student_information table has been altered successfully. Now last_name column can accept the null values, as shown in the below sn...
129. [ ON DELETE action ] [ ON UPDATE action ] } 130. [ DEFERRABLE |NOT DEFERRABLE ][ INITIALLY DEFERRED | INITIALLY IMMEDIATE ] 131. 132. and table_constraint is: 133. 134. [ CONSTRAINT constraint_name ] 135. { UNIQUE ( column_name [, ...] ) [ USING INDEX TABLESPACE tablespace ...
The not-null constraint in PostgreSQL ensures that a column can not contain any null value. This is a column constraint. No name can be defined to create a not-null constraint. This constraint is placed immediately after the data-type of a column. Any attempt to put NULL values in that ...
PostgreSQL Not-Null Constraint This tutorial works for PostgreSQL anywhere. If you need cloud Postgres, get ten databases free on Neon. Summary: in this tutorial, you will learn about PostgreSQL not-null constraints to ensure the values of a column are not null. Introduction to NULL In the da...
To create a column with NOT NULL Constraint, use the following syntax: CREATE TABLE tab_name( col_name DATA TYPE NOT NULL ); The above syntax states that you must specify the NOT NULL constraint after the data type to create a column that doesn't accept null values. ...
可以将连接命令中的参数在环境变量中指定;比如环境变量中配置如下,那么执行psql等同于执行psql -h 192.168.56.11 -p 5432 testdb postgres。 export PGDATABASE=testdb export PGHOST=192.168.56.11 export PGPORT=5432 export PGUSER=postgres 2、一些查看命令 #查看命令语法的帮助命令 \h #查看有哪些库 \l #...
postgres=#createtablepart_test(idint, infotext, crt_timetimestampnotnull);--分区列必须有not null约束CREATETABLE插入一批测试数据,模拟已经有数据了的主表 postgres=#insertintopart_testselectid,md5(random()::text),clock_timestamp()+(id||'hour')::intervalfromgenerate_series(1,10000) t(id);INSER...
UNIQUE constraint –ensure that values in a column or a group of columns are unique across the table. NOT NULL constraint –ensure values in a column are not NULL. DEFAULT constraint –specify a default value for a column using the DEFAULT constraint. Section 14. PostgreSQL Data Types in Dep...
ADD CONSTRAINT film_rental_rate_check CHECK (rental_rate > 0 AND rental_rate IS NOT NULL); 在Navicat 表设计器中,相同的约束如下: 结语 检查约束是一个确保 PostgreSQL 数据完整性的强大工具。通过定义数据必须遵守的规则,可以防止插入或修改无效数据,从而帮助维护数据库的准确性和一致性。将检查约束纳入...