2. NULL and Empty Values Before starting to write the SQL query, it’s essential to understand the distinctions betweenNULLand empty values (strings). NULLvalues in SQL represent missing or unknown data in a dat
INSERT INTO `k1` (`id`, `yb`) VALUES('1','100'); INSERT INTO `k1` (`id`, `yb`) VALUES('2','11'); INSERT INTO `k1` (`id`, `yb`) VALUES('3','5'); INSERT INTO `k1` (`id`, `yb`) VALUES('4','501'); INSERT INTO `k1` (`id`, `yb`) VALUES('5','1501');...
Agenten Generally, it’s best practice to put unique constraints on a table to prevent duplicate rows. However, you may find yourself working with a database where duplicate rows have been created through human error, a bug in your application, or uncleaned data from external sources. This t...
CREATE TABLE `test` (`ID` int(11) NOT NULL,`LIST` varchar(255) DEFAULT NULL,PRIMARY KEY (`ID`)) ENGINE=InnoDB DEFAULT CHARSET=utf8;-- --- Records of test-- ---INSERT INTO `test` VALUES ('1', 'AA,BB,CC');INSERT INTO `test` VALUES ('2', 'AA,BB');INSERT INTO `test` V...
FIND_IN_SET是 MySQL 中的一个字符串函数,用于在一个逗号分隔的字符串列表中查找指定的值,并返回其位置索引。如果未找到,则返回NULL。这个函数在 SQL Server 中没有直接的等价物,但可以通过使用CHARINDEX和STRING_SPLIT函数的组合来实现类似的功能。 基础概念 ...
SELECT INTERVAL(NULL,20,30,40,50,60); # -1 SELECT INTERVAL('c','b','d'); # 2 #elt函数与interval实现分组统计 CREATE TABLE `k1` ( `id` INT (11), `yb` INT (11) ); INSERT INTO `k1` (`id`, `yb`) VALUES('1','100'); ...
(4)匹配值的范围查询(Match a range of values):可以利用索引查找last name在Allen和Barrymore之间的人,仅仅使用索引中第1列。 (5)匹配部分精确而其它部分进行范围匹配(Match one part exactly and match a range on another part):可以利用索引查找last name为Allen,而first name以字母K开始的人。
SQL代码语句如下: CREATE TABLE `test1` ( `id` int(8) NOT NULL auto_increment, `name` varchar(255) NOT NULL, `list` varchar(255) NOT NULL, PRIMARY KEY (`id`) ); INSERT INTO `test1`(name,list) VALUES ('张三', '篮球,足球,羽毛球'); INSERT INTO `test1`(name,list) VALUES ('...
The SQL Coalesce Function: Handling Null Values What Is a NULL in SQL? How to Use Comparison Operators with NULLs in SQL Understanding the Use of NULL in SQL Three-Valued Logic How to Use the COALESCE() Function in SQL See also: How to Use LIKE in SQL How to Filter Rows without NULL...
测试表来说明find_in_set()和in的区别:CREATE TABLE `tb_test` ( `id` int(8) NOT NULL auto_increment, `name` varchar(255) NOT NULL, `list` varchar(255) NOT NULL, PRIMARY KEY (`id`) ); INSERT INTO `tb_test` VALUES (1, 'name', 'daodao,xiaohu,xiaoqin'); ...