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mysql中用来取余数的函数是_MySQL常用函数-单行处理函数-字符串处理函数(更新中...)...

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生活随笔收集整理的這篇文章主要介紹了 mysql中用来取余数的函数是_MySQL常用函数-单行处理函数-字符串处理函数(更新中...)... 小編覺得挺不錯(cuò)的,現(xiàn)在分享給大家,幫大家做個(gè)參考.

本篇文章用到的數(shù)據(jù)庫表

/* SQLyog Ultimate v12.09 (64 bit) MySQL - 5.7.23-log : Database - myemployees ********************************************************************* *//*!40101 SET NAMES utf8 */;/*!40101 SET SQL_MODE=''*/;/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */; /*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */; /*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */; /*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */; CREATE DATABASE /*!32312 IF NOT EXISTS*/`myemployees` /*!40100 DEFAULT CHARACTER SET utf8 */;USE `myemployees`;/*Table structure for table `employees` */DROP TABLE IF EXISTS `employees`;CREATE TABLE `employees` (`employee_id` int(6) NOT NULL AUTO_INCREMENT,`first_name` varchar(20) DEFAULT NULL,`last_name` varchar(25) DEFAULT NULL,`email` varchar(25) DEFAULT NULL,`phone_number` varchar(20) DEFAULT NULL,`job_id` varchar(10) DEFAULT NULL,`salary` double(10,2) DEFAULT NULL,`commission_pct` double(4,2) DEFAULT NULL,`manager_id` int(6) DEFAULT NULL,`department_id` int(4) DEFAULT NULL,`hiredate` datetime DEFAULT NULL,PRIMARY KEY (`employee_id`),KEY `dept_id_fk` (`department_id`),KEY `job_id_fk` (`job_id`),CONSTRAINT `dept_id_fk` FOREIGN KEY (`department_id`) REFERENCES `departments` (`department_id`),CONSTRAINT `job_id_fk` FOREIGN KEY (`job_id`) REFERENCES `jobs` (`job_id`) ) ENGINE=InnoDB AUTO_INCREMENT=209 DEFAULT CHARSET=utf8;/*Data for the table `employees` */insert into `employees`(`employee_id`,`first_name`,`last_name`,`email`,`phone_number`,`job_id`,`salary`,`commission_pct`,`manager_id`,`department_id`,`hiredate`) values (100,'Steven','K_ing','SKING','515.123.4567','AD_PRES',24000.00,NULL,NULL,90,'1992-04-03 00:00:00'),(101,'Neena','Kochhar','NKOCHHAR','515.123.4568','AD_VP',17000.00,NULL,100,90,'1992-04-03 00:00:00'),(102,'Lex','De Haan','LDEHAAN','515.123.4569','AD_VP',17000.00,NULL,100,90,'1992-04-03 00:00:00'),(103,'Alexander','Hunold','AHUNOLD','590.423.4567','IT_PROG',9000.00,NULL,102,60,'1992-04-03 00:00:00'),(104,'Bruce','Ernst','BERNST','590.423.4568','IT_PROG',6000.00,NULL,103,60,'1992-04-03 00:00:00'),(105,'David','Austin','DAUSTIN','590.423.4569','IT_PROG',4800.00,NULL,103,60,'1998-03-03 00:00:00'),(106,'Valli','Pataballa','VPATABAL','590.423.4560','IT_PROG',4800.00,NULL,103,60,'1998-03-03 00:00:00'),(107,'Diana','Lorentz','DLORENTZ','590.423.5567','IT_PROG',4200.00,NULL,103,60,'1998-03-03 00:00:00'),(108,'Nancy','Greenberg','NGREENBE','515.124.4569','FI_MGR',12000.00,NULL,101,100,'1998-03-03 00:00:00'),(109,'Daniel','Faviet','DFAVIET','515.124.4169','FI_ACCOUNT',9000.00,NULL,108,100,'1998-03-03 00:00:00'),(110,'John','Chen','JCHEN','515.124.4269','FI_ACCOUNT',8200.00,NULL,108,100,'2000-09-09 00:00:00'),(111,'Ismael','Sciarra','ISCIARRA','515.124.4369','FI_ACCOUNT',7700.00,NULL,108,100,'2000-09-09 00:00:00'),(112,'Jose Manuel','Urman','JMURMAN','515.124.4469','FI_ACCOUNT',7800.00,NULL,108,100,'2000-09-09 00:00:00'),(113,'Luis','Popp','LPOPP','515.124.4567','FI_ACCOUNT',6900.00,NULL,108,100,'2000-09-09 00:00:00'),(114,'Den','Raphaely','DRAPHEAL','515.127.4561','PU_MAN',11000.00,NULL,100,30,'2000-09-09 00:00:00'),(115,'Alexander','Khoo','AKHOO','515.127.4562','PU_CLERK',3100.00,NULL,114,30,'2000-09-09 00:00:00'),(116,'Shelli','Baida','SBAIDA','515.127.4563','PU_CLERK',2900.00,NULL,114,30,'2000-09-09 00:00:00'),(117,'Sigal','Tobias','STOBIAS','515.127.4564','PU_CLERK',2800.00,NULL,114,30,'2000-09-09 00:00:00'),(118,'Guy','Himuro','GHIMURO','515.127.4565','PU_CLERK',2600.00,NULL,114,30,'2000-09-09 00:00:00'),(119,'Karen','Colmenares','KCOLMENA','515.127.4566','PU_CLERK',2500.00,NULL,114,30,'2000-09-09 00:00:00'),(120,'Matthew','Weiss','MWEISS','650.123.1234','ST_MAN',8000.00,NULL,100,50,'2004-02-06 00:00:00'),(121,'Adam','Fripp','AFRIPP','650.123.2234','ST_MAN',8200.00,NULL,100,50,'2004-02-06 00:00:00'),(122,'Payam','Kaufling','PKAUFLIN','650.123.3234','ST_MAN',7900.00,NULL,100,50,'2004-02-06 00:00:00'),(123,'Shanta','Vollman','SVOLLMAN','650.123.4234','ST_MAN',6500.00,NULL,100,50,'2004-02-06 00:00:00'),(124,'Kevin','Mourgos','KMOURGOS','650.123.5234','ST_MAN',5800.00,NULL,100,50,'2004-02-06 00:00:00'),(125,'Julia','Nayer','JNAYER','650.124.1214','ST_CLERK',3200.00,NULL,120,50,'2004-02-06 00:00:00'),(126,'Irene','Mikkilineni','IMIKKILI','650.124.1224','ST_CLERK',2700.00,NULL,120,50,'2004-02-06 00:00:00'),(127,'James','Landry','JLANDRY','650.124.1334','ST_CLERK',2400.00,NULL,120,50,'2004-02-06 00:00:00'),(128,'Steven','Markle','SMARKLE','650.124.1434','ST_CLERK',2200.00,NULL,120,50,'2004-02-06 00:00:00'),(129,'Laura','Bissot','LBISSOT','650.124.5234','ST_CLERK',3300.00,NULL,121,50,'2004-02-06 00:00:00'),(130,'Mozhe','Atkinson','MATKINSO','650.124.6234','ST_CLERK',2800.00,NULL,121,50,'2004-02-06 00:00:00'),(131,'James','Marlow','JAMRLOW','650.124.7234','ST_CLERK',2500.00,NULL,121,50,'2004-02-06 00:00:00'),(132,'TJ','Olson','TJOLSON','650.124.8234','ST_CLERK',2100.00,NULL,121,50,'2004-02-06 00:00:00'),(133,'Jason','Mallin','JMALLIN','650.127.1934','ST_CLERK',3300.00,NULL,122,50,'2004-02-06 00:00:00'),(134,'Michael','Rogers','MROGERS','650.127.1834','ST_CLERK',2900.00,NULL,122,50,'2002-12-23 00:00:00'),(135,'Ki','Gee','KGEE','650.127.1734','ST_CLERK',2400.00,NULL,122,50,'2002-12-23 00:00:00'),(136,'Hazel','Philtanker','HPHILTAN','650.127.1634','ST_CLERK',2200.00,NULL,122,50,'2002-12-23 00:00:00'),(137,'Renske','Ladwig','RLADWIG','650.121.1234','ST_CLERK',3600.00,NULL,123,50,'2002-12-23 00:00:00'),(138,'Stephen','Stiles','SSTILES','650.121.2034','ST_CLERK',3200.00,NULL,123,50,'2002-12-23 00:00:00'),(139,'John','Seo','JSEO','650.121.2019','ST_CLERK',2700.00,NULL,123,50,'2002-12-23 00:00:00'),(140,'Joshua','Patel','JPATEL','650.121.1834','ST_CLERK',2500.00,NULL,123,50,'2002-12-23 00:00:00'),(141,'Trenna','Rajs','TRAJS','650.121.8009','ST_CLERK',3500.00,NULL,124,50,'2002-12-23 00:00:00'),(142,'Curtis','Davies','CDAVIES','650.121.2994','ST_CLERK',3100.00,NULL,124,50,'2002-12-23 00:00:00'),(143,'Randall','Matos','RMATOS','650.121.2874','ST_CLERK',2600.00,NULL,124,50,'2002-12-23 00:00:00'),(144,'Peter','Vargas','PVARGAS','650.121.2004','ST_CLERK',2500.00,NULL,124,50,'2002-12-23 00:00:00'),(145,'John','Russell','JRUSSEL','011.44.1344.429268','SA_MAN',14000.00,0.40,100,80,'2002-12-23 00:00:00'),(146,'Karen','Partners','KPARTNER','011.44.1344.467268','SA_MAN',13500.00,0.30,100,80,'2002-12-23 00:00:00'),(147,'Alberto','Errazuriz','AERRAZUR','011.44.1344.429278','SA_MAN',12000.00,0.30,100,80,'2002-12-23 00:00:00'),(148,'Gerald','Cambrault','GCAMBRAU','011.44.1344.619268','SA_MAN',11000.00,0.30,100,80,'2002-12-23 00:00:00'),(149,'Eleni','Zlotkey','EZLOTKEY','011.44.1344.429018','SA_MAN',10500.00,0.20,100,80,'2002-12-23 00:00:00'),(150,'Peter','Tucker','PTUCKER','011.44.1344.129268','SA_REP',10000.00,0.30,145,80,'2014-03-05 00:00:00'),(151,'David','Bernstein','DBERNSTE','011.44.1344.345268','SA_REP',9500.00,0.25,145,80,'2014-03-05 00:00:00'),(152,'Peter','Hall','PHALL','011.44.1344.478968','SA_REP',9000.00,0.25,145,80,'2014-03-05 00:00:00'),(153,'Christopher','Olsen','COLSEN','011.44.1344.498718','SA_REP',8000.00,0.20,145,80,'2014-03-05 00:00:00'),(154,'Nanette','Cambrault','NCAMBRAU','011.44.1344.987668','SA_REP',7500.00,0.20,145,80,'2014-03-05 00:00:00'),(155,'Oliver','Tuvault','OTUVAULT','011.44.1344.486508','SA_REP',7000.00,0.15,145,80,'2014-03-05 00:00:00'),(156,'Janette','K_ing','JKING','011.44.1345.429268','SA_REP',10000.00,0.35,146,80,'2014-03-05 00:00:00'),(157,'Patrick','Sully','PSULLY','011.44.1345.929268','SA_REP',9500.00,0.35,146,80,'2014-03-05 00:00:00'),(158,'Allan','McEwen','AMCEWEN','011.44.1345.829268','SA_REP',9000.00,0.35,146,80,'2014-03-05 00:00:00'),(159,'Lindsey','Smith','LSMITH','011.44.1345.729268','SA_REP',8000.00,0.30,146,80,'2014-03-05 00:00:00'),(160,'Louise','Doran','LDORAN','011.44.1345.629268','SA_REP',7500.00,0.30,146,80,'2014-03-05 00:00:00'),(161,'Sarath','Sewall','SSEWALL','011.44.1345.529268','SA_REP',7000.00,0.25,146,80,'2014-03-05 00:00:00'),(162,'Clara','Vishney','CVISHNEY','011.44.1346.129268','SA_REP',10500.00,0.25,147,80,'2014-03-05 00:00:00'),(163,'Danielle','Greene','DGREENE','011.44.1346.229268','SA_REP',9500.00,0.15,147,80,'2014-03-05 00:00:00'),(164,'Mattea','Marvins','MMARVINS','011.44.1346.329268','SA_REP',7200.00,0.10,147,80,'2014-03-05 00:00:00'),(165,'David','Lee','DLEE','011.44.1346.529268','SA_REP',6800.00,0.10,147,80,'2014-03-05 00:00:00'),(166,'Sundar','Ande','SANDE','011.44.1346.629268','SA_REP',6400.00,0.10,147,80,'2014-03-05 00:00:00'),(167,'Amit','Banda','ABANDA','011.44.1346.729268','SA_REP',6200.00,0.10,147,80,'2014-03-05 00:00:00'),(168,'Lisa','Ozer','LOZER','011.44.1343.929268','SA_REP',11500.00,0.25,148,80,'2014-03-05 00:00:00'),(169,'Harrison','Bloom','HBLOOM','011.44.1343.829268','SA_REP',10000.00,0.20,148,80,'2014-03-05 00:00:00'),(170,'Tayler','Fox','TFOX','011.44.1343.729268','SA_REP',9600.00,0.20,148,80,'2014-03-05 00:00:00'),(171,'William','Smith','WSMITH','011.44.1343.629268','SA_REP',7400.00,0.15,148,80,'2014-03-05 00:00:00'),(172,'Elizabeth','Bates','EBATES','011.44.1343.529268','SA_REP',7300.00,0.15,148,80,'2014-03-05 00:00:00'),(173,'Sundita','Kumar','SKUMAR','011.44.1343.329268','SA_REP',6100.00,0.10,148,80,'2014-03-05 00:00:00'),(174,'Ellen','Abel','EABEL','011.44.1644.429267','SA_REP',11000.00,0.30,149,80,'2014-03-05 00:00:00'),(175,'Alyssa','Hutton','AHUTTON','011.44.1644.429266','SA_REP',8800.00,0.25,149,80,'2014-03-05 00:00:00'),(176,'Jonathon','Taylor','JTAYLOR','011.44.1644.429265','SA_REP',8600.00,0.20,149,80,'2014-03-05 00:00:00'),(177,'Jack','Livingston','JLIVINGS','011.44.1644.429264','SA_REP',8400.00,0.20,149,80,'2014-03-05 00:00:00'),(178,'Kimberely','Grant','KGRANT','011.44.1644.429263','SA_REP',7000.00,0.15,149,NULL,'2014-03-05 00:00:00'),(179,'Charles','Johnson','CJOHNSON','011.44.1644.429262','SA_REP',6200.00,0.10,149,80,'2014-03-05 00:00:00'),(180,'Winston','Taylor','WTAYLOR','650.507.9876','SH_CLERK',3200.00,NULL,120,50,'2014-03-05 00:00:00'),(181,'Jean','Fleaur','JFLEAUR','650.507.9877','SH_CLERK',3100.00,NULL,120,50,'2014-03-05 00:00:00'),(182,'Martha','Sullivan','MSULLIVA','650.507.9878','SH_CLERK',2500.00,NULL,120,50,'2014-03-05 00:00:00'),(183,'Girard','Geoni','GGEONI','650.507.9879','SH_CLERK',2800.00,NULL,120,50,'2014-03-05 00:00:00'),(184,'Nandita','Sarchand','NSARCHAN','650.509.1876','SH_CLERK',4200.00,NULL,121,50,'2014-03-05 00:00:00'),(185,'Alexis','Bull','ABULL','650.509.2876','SH_CLERK',4100.00,NULL,121,50,'2014-03-05 00:00:00'),(186,'Julia','Dellinger','JDELLING','650.509.3876','SH_CLERK',3400.00,NULL,121,50,'2014-03-05 00:00:00'),(187,'Anthony','Cabrio','ACABRIO','650.509.4876','SH_CLERK',3000.00,NULL,121,50,'2014-03-05 00:00:00'),(188,'Kelly','Chung','KCHUNG','650.505.1876','SH_CLERK',3800.00,NULL,122,50,'2014-03-05 00:00:00'),(189,'Jennifer','Dilly','JDILLY','650.505.2876','SH_CLERK',3600.00,NULL,122,50,'2014-03-05 00:00:00'),(190,'Timothy','Gates','TGATES','650.505.3876','SH_CLERK',2900.00,NULL,122,50,'2014-03-05 00:00:00'),(191,'Randall','Perkins','RPERKINS','650.505.4876','SH_CLERK',2500.00,NULL,122,50,'2014-03-05 00:00:00'),(192,'Sarah','Bell','SBELL','650.501.1876','SH_CLERK',4000.00,NULL,123,50,'2014-03-05 00:00:00'),(193,'Britney','Everett','BEVERETT','650.501.2876','SH_CLERK',3900.00,NULL,123,50,'2014-03-05 00:00:00'),(194,'Samuel','McCain','SMCCAIN','650.501.3876','SH_CLERK',3200.00,NULL,123,50,'2014-03-05 00:00:00'),(195,'Vance','Jones','VJONES','650.501.4876','SH_CLERK',2800.00,NULL,123,50,'2014-03-05 00:00:00'),(196,'Alana','Walsh','AWALSH','650.507.9811','SH_CLERK',3100.00,NULL,124,50,'2014-03-05 00:00:00'),(197,'Kevin','Feeney','KFEENEY','650.507.9822','SH_CLERK',3000.00,NULL,124,50,'2014-03-05 00:00:00'),(198,'Donald','OConnell','DOCONNEL','650.507.9833','SH_CLERK',2600.00,NULL,124,50,'2014-03-05 00:00:00'),(199,'Douglas','Grant','DGRANT','650.507.9844','SH_CLERK',2600.00,NULL,124,50,'2014-03-05 00:00:00'),(200,'Jennifer','Whalen','JWHALEN','515.123.4444','AD_ASST',4400.00,NULL,101,10,'2016-03-03 00:00:00'),(201,'Michael','Hartstein','MHARTSTE','515.123.5555','MK_MAN',13000.00,NULL,100,20,'2016-03-03 00:00:00'),(202,'Pat','Fay','PFAY','603.123.6666','MK_REP',6000.00,NULL,201,20,'2016-03-03 00:00:00'),(203,'Susan','Mavris','SMAVRIS','515.123.7777','HR_REP',6500.00,NULL,101,40,'2016-03-03 00:00:00'),(204,'Hermann','Baer','HBAER','515.123.8888','PR_REP',10000.00,NULL,101,70,'2016-03-03 00:00:00'),(205,'Shelley','Higgins','SHIGGINS','515.123.8080','AC_MGR',12000.00,NULL,101,110,'2016-03-03 00:00:00'),(206,'William','Gietz','WGIETZ','515.123.8181','AC_ACCOUNT',8300.00,NULL,205,110,'2016-03-03 00:00:00'),(207,'xingxing','zhou','554555@qq.com',NULL,NULL,NULL,NULL,NULL,NULL,NULL),(208,'xiaohu',NULL,'555145@126.com',NULL,NULL,NULL,NULL,NULL,NULL,NULL);/*!40101 SET SQL_MODE=@OLD_SQL_MODE */; /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */; /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

1 length()：獲取字節(jié)數(shù)

說明：我們在MySQL中創(chuàng)建數(shù)據(jù)庫時(shí)，有一個(gè)操作就是要指定數(shù)據(jù)庫的字符集，而這里的獲取字節(jié)數(shù)的函數(shù)——length()就和這個(gè)字符集相關(guān)的。

在這里簡單說一下常見的MySQL字符集一個(gè)字符所占用的字節(jié)數(shù)。(詳見文章：MySQL字符集，文章地址：)

utf8(注意：不是utf-8)：數(shù)字、字母占用一個(gè)字符，常見的中文字符占用3個(gè)字節(jié)，不能存儲(chǔ)占用4個(gè)字節(jié)的生僻漢字、emoji等。
utf8mb4（真utf-8）：數(shù)字、字母占用一個(gè)字符，常見的中文字符占用3個(gè)字節(jié)，但是可以存儲(chǔ)占用4個(gè)字節(jié)的生僻漢字、emoji等。
gbk：數(shù)字、字母占用一個(gè)字符，常見的中文字符占用2個(gè)字節(jié)，不能存儲(chǔ)占用4個(gè)字節(jié)的生僻漢字、emoji等。（沒想到吧，gbk不能存儲(chǔ)中文生僻字）

另外，再說一個(gè)命令：SHOW VARIABLES LIKE '%char%' ——查看系統(tǒng)字符集設(shè)置，包括所有的字符集設(shè)置：（關(guān)于這個(gè)字符集的說明，詳見文章：MySQL字符集，文章地址：）

當(dāng)前我的數(shù)據(jù)庫是utf8md4字符集，其他的字符集自行測試。

（1）數(shù)字、字母、常見中文字符

#運(yùn)行結(jié)果：6 SELECT LENGTH("aaa111")#運(yùn)行結(jié)果：6 SELECT LENGTH("老王")

（2）生僻字

注意：這個(gè)生僻字需要從這里拷貝過去（" "），不能直接打出來（不是你用拼音打出來的"康熙"的“熙”，這是一個(gè)異體字。另外，本人測試過，這個(gè)異體字在知乎上可能會(huì)顯示不出來，看我的截圖就行。）。

#運(yùn)行結(jié)果：4 SELECT LENGTH(" ");

2 concat()

1、函數(shù)的使用

由于在MySQL中，"+"只是做加法運(yùn)算的，因此拼接字符串就不能使用“+”了，需要使用concat()函數(shù)。

#錯(cuò)誤的寫法，不能使用"+" SELECT last_name+first_name AS "姓名" FROM employees;#正確的姿勢 SELECT CONCAT(last_name,first_name) AS "姓名" FROM employees;

2、使用注意

該函數(shù)在進(jìn)行拼接時(shí)，只要拼接的字段有null值，則拼接結(jié)果一定為null，必須使用ifnull()函數(shù)進(jìn)行處理！(關(guān)于ifnull函數(shù)的用法，詳見文章：ifnull()，文章地址：)

對(duì)null值不進(jìn)行處理時(shí)，拼接結(jié)果為null：

#不對(duì)null值進(jìn)行處理 SELECT last_name,first_name,CONCAT(last_name, first_name) AS "姓名" FROMemployees ;

對(duì)null值進(jìn)行處理后，可正常拼接

#對(duì)null值進(jìn)行處理 SELECT last_name,first_name,CONCAT(IFNULL(last_name, ""), first_name) AS "姓名" FROMemployees ;

3 upper()、lower()

1、該函數(shù)的作用

upper()：返回字符串str根據(jù)當(dāng)前字符集映射所有字符為大寫。簡言之，就是將字符串中所有的字母字符轉(zhuǎn)換為大寫

lower()：與上面的upper()相反，轉(zhuǎn)換為小寫。

2、使用

【案例1】將姓變?yōu)榇髮?#xff0c;名變?yōu)樾?#xff0c;然后進(jìn)行拼接

#SQLyog使用技巧：F12鍵可對(duì)SQL語句進(jìn)行格式化排版 SELECT UPPER(last_name) AS '姓',LOWER(first_name) AS '名' ,CONCAT(UPPER(last_name), "_", LOWER(first_name)) AS "姓名" FROMemployees ;

4 substr()( 或substring() ）

首先說明一下：MySQL中的下標(biāo)都是從1開始的。

1、函數(shù)作用：截取字符串。該方法有四個(gè)重載方法，如下圖所示：

2、使用

（1）SUBSTR(str,pos)：截取指定索引pos處后所有的字符串。

【案例1】截取字符串"李莫愁愛上了陸展元"中的"陸展元"

#注意：下標(biāo)是從1開始的 SELECT SUBSTR("李莫愁愛上了陸展元",7) AS out_put;

（2）SUBSTR(str,pos,len)：從指定索引pos處開始截取字符串str，截取字符長度為len。

【案例1】截取字符串""李莫愁愛上了陸展元"中的"李莫愁"

SELECT SUBSTR("李莫愁愛上了陸展元",1,3) AS out_put;

【案例2】姓名中首字母大寫，其他字符小寫，然后用_拼接

SELECT last_name,first_name,CONCAT(UPPER(SUBSTR(last_name, 1, 1)),"_",LOWER(SUBSTR(last_name, 2)),"_",LOWER(first_name)) AS out_put FROMemployees ;

5 instr()

作用：返回此字符串在指定字符串中第一次出現(xiàn)的索引

#運(yùn)行結(jié)果3 SELECT INSTR("我是張三，我的名字叫張三三","張三") AS result;

6 trim()

作用1：去除前后空格

#運(yùn)行結(jié)果：13 SELECT LENGTH(TRIM(" 我是張三 ")) AS result;

作用2：去除前后指定的字符串

#運(yùn)行結(jié)果：張三bb SELECT TRIM('a' FROM 'aaaaa張三bbaaa') AS result; ? #注意：如果寫兩個(gè)aa，運(yùn)行結(jié)果就是 a張三bba #兩個(gè)兩個(gè)進(jìn)行匹配，最后還剩下一個(gè)a沒有被匹配上，所以就留下了 SELECT TRIM('aa' FROM 'aaaaa張三bbaaa') AS result;

7 lpad()

作用：左填充。當(dāng)字符串長度不足指定的長度時(shí)，左填充指定的字符串

注意：如果字符串長度超過指定長度，則會(huì)進(jìn)行左起開始截?cái)?#xff01;

#運(yùn)行結(jié)果：00100 SELECT LPAD("100",5,"0") AS result; ? #字符串長度超長，運(yùn)行結(jié)果：12345 SELECT LPAD("1234567",5,"0") AS result;

8 rpad()

作用：右填充。當(dāng)字符串長度不足指定的長度時(shí)，左填充指定的字符串

注意：如果字符串長度超過指定長度，則會(huì)進(jìn)行左起開始截?cái)?#xff01;

#運(yùn)行結(jié)果：10000 SELECT RPAD("100",5,"0") AS result;#字符串本身的長度已經(jīng)超過了指定長度，左起開始截?cái)?#所以運(yùn)行結(jié)果是：10 SELECT RPAD("100",2,"0") AS result;

9 replace()

作用：替換字符串

#運(yùn)行結(jié)果：我是李四，我的名字叫李四三 SELECT REPLACE("我是張三，我的名字叫張三三","張三","李四") AS result;

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