SQL基础(三)

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非空约束对数据插入的影响：

mysql> insert into t_debt(fnumber,fperson) values('1','Jim');1364 - Field 'famount' doesn't have a default valuemysql> insert into t_debt(fnumber,famount,fperson) values('1',200,'Jim');Query OK, 1 row affectedmysql> select * from t_debt;+---------+---------+---------+| fnumber | famount | fperson |+---------+---------+---------+| 1       | 200     | Jim     |+---------+---------+---------+1 row in set

主键约束对数据插入的影响：

mysql> insert into t_debt(fnumber,famount,fperson) values('1',300,'Jim');1062 - Duplicate entry '1' for key 'PRIMARY'mysql> insert into t_debt(fnumber,famount,fperson) values('2',300,'Jim');Query OK, 1 row affectedmysql> select * from t_debt;+---------+---------+---------+| fnumber | famount | fperson |+---------+---------+---------+| 1       | 200     | Jim     || 2       | 300     | Jim     |+---------+---------+---------+2 rows in set

外键约束对数据插入的影响：

mysql> insert into t_debt(fnumber,famount,fperson) values('3',100,'Jerry');1452 - Cannot add or update a child row: a foreign key constraint fails (`learnsql`.`t_debt`, CONSTRAINT `t_debt_ibfk_1` FOREIGN KEY (`fperson`) REFERENCES `t_person` (`fname`))mysql> insert into t_debt(fnumber,famount,fperson) values('3',100,'Tom');Query OK, 1 row affectedmysql> select * from t_debt;+---------+---------+---------+| fnumber | famount | fperson |+---------+---------+---------+| 1       | 200     | Jim     || 2       | 300     | Jim     || 3       | 100     | Tom     |+---------+---------+---------+3 rows in set

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