SELECTcolumn_name,IF(column_nameISNULL,'Empty','Not Empty')ASstatusFROMtable_name; 使用CASE语句检查列是否为空: 代码语言:sql AI代码解释 SELECTcolumn_name,CASEWHENcolumn_nameISNULLTHEN'Empty'ELSE'Not Empty'ENDASstatusFROMtable_name; 在这些查询中,我们使用IF和CASE语句来根据列的值返回相应的结果,以...
CREATE TABLE `t_student` ( `no` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) DEFAULT NULL, `cno` int(11) DEFAULT NULL, PRIMARY KEY (`no`), KEY `cno` (`cno`), CONSTRAINT `t_student_ibfk_1` FOREIGN KEY (`cno`) REFERENCES `t_class` (`classno`) ) ENGINE=InnoDB AUTO...
SELECT column_name, IF(column_name IS NULL, 'Empty', 'Not Empty') AS status FROM table_name; 1. 使用CASE语句检查列是否为空: AI检测代码解析 SELECT column_name, CASE WHEN column_name IS NULL THEN 'Empty' ELSE 'Not Empty' END AS status FROM table_name; 1. 2. 3. 4. 5. 6. 在...
0 运行 AI代码解释 mysql> CREATE TABLE `test` ( -> id` int(10) NOT NULL AUTO_INCREMENT COMMENT '主键ID', -> `uniq_flag` varchar(64) NOT NULL DEFAULT ''COMMENT '唯一建', -> PRIMARY KEY (`id`), -> UNIQUE KEY `uniq_flag` (`uniq_flag`) USING BTREE -> ) ENGINE=InnoDB DEFAULT...
Empty set (0.00sec) (root@localhost mysql3306.sock)[zlm]>select* from test_null where null<>null; Empty set (0.00sec) (root@localhost mysql3306.sock)[zlm]>select* from test_null where null<=>null; +---+---+ | id | name | +---...
(root@localhost mysql3306.sock)[zlm]>select * from test_null where name is not null;+---+---+| id | name |+---+---+| 1 | zlm |+---+---+1 row in set (0.00 sec)(root@localhost mysql3306.sock)[zlm]>select * f...
ⅠMySQL约束条件 【一】什么是约束条件 约束条件:限制表中的数据,保证添加到数据表中的数据准确和可靠性!凡是不符合约束的数据,插入时就会失败! 约束条件在创建表时可以使用, 也可以修改表的时候添加约束条件 【二】约束条件概览 null 和 not null 为空和不为空 限制
Empty set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select * from test_null where name is null; +---+---+ id | name | +---+---+ 2 | NULL | +---+---+ 1 row in set (0.00 sec) (root@localhost mysql3306.sock)[zlm]>select * from test_null where name is not ...
通常能听到的答案是使用了NULL值的列将会使索引失效,但是如果实际测试过一下,你就知道IS NULL会使用索引.所以上述说法有漏洞.着急的人拉到最下边看结论 Preface Null is a special constraint of columns.The columns in table will be added null constrain if you do not define the column with “not null”...
set_not_empty() : Opt_trace_struct set_not_started() : TABLE set_not_yet_determined() : Gtid_specification set_notnull() : Field set_nth_dir_entry() : lob::z_frag_page_t set_null() : Column_text, dd::Raw_record, Field, Gtid_set_or_null, Item_param, lob::z_frag_entry_t...