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_n
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: 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. 在这些查询中,我们...
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...
(root@localhost mysql3306.sock)[zlm]>select * from test_null where null=null;Empty set (0.00 sec)(root@localhost mysql3306.sock)[zlm]>select * from test_null where null<>null;Empty set (0.00 sec)(root@localhost mysql3306.sock)...
test_nullwherename=null;23Emptyset(0.00sec)2425(root@localhostmysql3306.sock)[zlm]>select*fromtest_nullwherenameisnull;26+---+---+27|id|name|28+---+---+29|2|NULL|30+---+---+311rowinset(0.00sec)3233(root@localhostmysql3306.sock)[zlm]>select*fromtest_nullwherenameisnotnull;34+...
NOT NULL 标识该字段不能为空 UNIQUE KEY (UK) 标识该字段的值是唯一的 AUTO_INCREMENT 标识该字段的值自动增长(整数类型,而且为主键) DEFAULT 为该字段设置默认值 UNSIGNED 无符号 ZEROFILL 使用0填充 说明 1. 是否允许为空,默认NULL,可设置NOT NULL,字段不允许为空,必须赋值 ...
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 ...
NULL | Daemon | 30527 | Waiting on empty queue | NULL | | 14 | root | localhost | NULL | Query | 0 | starting | show full processlist | +---+---+---+---+---+---+---+---+ 2 rows in set (0.00 sec) # 注意,针对以上查看结果进行详细字段说明: ① Id 当用户登录mysql时...
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...