/*test=# alter table tbl_check add constraint ck_tbl_check_a check (a > 0); ERROR: check constraint "ck_tbl_check_a" is violated by some row test=# delete from tbl_check where a <= 0; DELETE 1 test=# alter table tbl_check add constraint ck_tbl_check_a check (a > 0); ALT...
ADDRESS CHAR(50), SALARY REAL ); 1. 2. 3. 4. 5. 6. 7. 如,以下PostgreSQL语句创建一个名为DEPARTMENT1的新表,该表将添加三列, EMP_ID列是外键,它引用表COMPANY6的ID字段。 CREATE TABLE DEPARTMENT1( ID INT PRIMARY KEY NOT NULL, DEPT CHAR(50) NOT NULL, EMP_ID INT references COMPANY6(I...
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...
In PostgreSQL, theNOT NULLconstraint makes sure that the column should accept only non-null values. For instance, if a column is created with a NOT NULL constraint, then attempting to insert a NULL value to that column will throw an error. Moreover, the NOT NULL constraint prevents users f...
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 ...
ERROR:conflicting key value violates exclusion constraint"company7_name_age_excl"DETAIL:Key(name,age)=(Paul,42)conflictswithexisting key(name,age)=(Paul,32). 删除约束 删除约束必须知道约束名称,已经知道名称来删除约束很简单,如果不知道名称,则需要找到系统生成的名称,使用\d 表名可以找到这些信息。
ID INT PRIMARY KEY NOT NULL, NAME TEXT NOT NULL, AGE INT NOT NULL, ADDRESS CHAR(50), SALARY REAL ); UNIQUE 约束 UNIQUE 约束可以设置列是唯一的,避免同一列出现重复值。 实例 下面实例创建了一张新表叫 COMPANY3,添加了 5 个字段,其中 AGE 设置为 UNIQUE,因此你不能添加两条有相同年龄的记录: ...
ERROR: null value in column "a" violates not-null constraint DETAIL: Failing row contains (null, 3).test=# select * from tbl_null;a | b ---+--- 1 | 1 2 | (2 rows)*/ 2.NOT NULL约束增加 已存在的字段设置NOT NULL约束前必须先删除为NULL的数据⾏。/* test=# alter table tbl...
PostgreSQL NOT NULL constraints To control whether a column can accept NULL, you use theNOT NULLconstraint: CREATE TABLEtable_name(...column_name data_type NOTNULL,...); If a column has aNOT NULLconstraint, any attempt toinsertorupdateNULL in the column will result in an error. ...
In PostgreSQL, the constraints are used to apply some rules on the table’s column. In Postgres, theNOT NULLconstraint prevents NULL entries from being inserted into a column. In simple terms, the table columns declared with aNOT NULLconstraint take only non-null entries. In Postgres, theNOT...