搜索到
78
篇与
的结果
-
内连接，左连接，右连接作用及区别 内连接就是普通的查询，例如1.加inner join的：SELECT S.SName,C.CourseID,C.GradeFrom Sc AS CINNER JOIN Students AS SONC.StudentID = S.SNo2.不加inner join的SELECT Students.SName, Sc.CourseID, Sc.GradeFROMStudents,ScWHEREStudents.SNo = Sc.StudentID外连接与普通连接的区别：普通连接只输出满足连接条件的元组，外连接操作以指定表为连接主题，将主体表中不满足连接条件的元组一并输出。外连接又分为左连接和右连接：左连接：SELECT S.SName,C.CourseID,C.Grade From Students AS S INNER JOIN Sc AS C ON C.StudentID <> S.SNo SELECT S.SName,C.CourseID,C.Grade From Sc AS C LEFT JOIN Students AS S ON C.StudentID = S.SNo //左连接就是以from左边为主，拿上面两个例子来说，第一种是以学生（students）为主，假如学生成绩为空，也能查询到学生信息，只不过成绩为空。而第二种则是以成绩为主（sc）所以先查学生成绩，如果成绩为空就算学生存在，也查不到记录。右连接：SELECT Titles.Title_id, Titles.Title, Publishers.Pub_name FROM titles RIGHT OUTER JOIN Publishers ON Titles.Pub_id = Publishers.Pub_id 右连接就是以from右边为主，与左连接类似。————————————————版权声明：本文为CSDN博主「一生所Ai」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。原文链接：https://blog.csdn.net/qq_40180411/article/details/81431209 -
时间筛选 MySQL中获取天、周、月等数据1.今天select * from 表名 where to_days(时间字段名) = to_days(now());2.昨天SELECT * FROM 表名 WHERE TO_DAYS( NOW( ) ) - TO_DAYS( 时间字段名) <= 13.近7天SELECT * FROM 表名 where DATE_SUB(CURDATE(), INTERVAL 7 DAY) <= date(时间字段名)4.近30天SELECT * FROM 表名 where DATE_SUB(CURDATE(), INTERVAL 30 DAY) <= date(时间字段名)5.本月SELECT * FROM 表名 WHERE DATE_FORMAT( 时间字段名, '%Y%m' ) = DATE_FORMAT( CURDATE( ) , '%Y%m' )6.上一月SELECT * FROM 表名 WHERE PERIOD_DIFF( date_format( now( ) , '%Y%m' ) , date_format( 时间字段名, '%Y%m' ) ) =17.查询本季度数据select * from ht_invoice_information where QUARTER(create_date)=QUARTER(now());8.查询上季度数据select * from ht_invoice_information where QUARTER(create_date)=QUARTER(DATE_SUB(now(),interval 1 QUARTER));9.查询本年数据select * from ht_invoice_information where YEAR(create_date)=YEAR(NOW());10.查询上年数据select * from ht_invoice_information where year(create_date)=year(date_sub(now(),interval 1 year));11.查询当前这周的数据SELECT name,submittime FROM enterprise WHERE YEARWEEK(date_format(submittime,'%Y-%m-%d')) = YEARWEEK(now());查询本周所有的数据(本周第一天是周一)SELECT * FROM task WHERE YEARWEEK(date_format(时间字段,'%Y-%m-%d'),1) = YEARWEEK(now(),1);查询本周所有的数据(本周第一天是周日)SELECT * FROM task WHERE YEARWEEK(date_format(时间字段,'%Y-%m-%d')) = YEARWEEK(now());12.查询上周的数据SELECT name,submittime FROM enterprise WHERE YEARWEEK(date_format(submittime,'%Y-%m-%d')) = YEARWEEK(now())-1;13.查询上个月的数据select name,submittime from enterprise where date_format(submittime,'%Y-%m')=date_format(DATE_SUB(curdate(), INTERVAL 1 MONTH),'%Y-%m')select * from user where DATE_FORMAT(pudate,'%Y%m') = DATE_FORMAT(CURDATE(),'%Y%m') ;select * from user where WEEKOFYEAR(FROM_UNIXTIME(pudate,'%y-%m-%d')) = WEEKOFYEAR(now())select * from user where MONTH(FROM_UNIXTIME(pudate,'%y-%m-%d')) = MONTH(now())select * from user where YEAR(FROM_UNIXTIME(pudate,'%y-%m-%d')) = YEAR(now()) and MONTH(FROM_UNIXTIME(pudate,'%y-%m-%d')) = MONTH(now())select * from user where pudate between 上月最后一天 and 下月第一天14.查询当前月份的数据select name,submittime from enterprise where date_format(submittime,'%Y-%m')=date_format(now(),'%Y-%m')15.查询距离当前现在6个月的数据select name,submittime from enterprise where submittime between date_sub(now(),interval 6 month) and now();select curdate(); --获取当前日期select last_day(curdate()); --获取当月最后一天。select DATE_ADD(curdate(),interval -day(curdate())+1 day); --获取本月第一天select date_add(curdate()-day(curdate())+1,interval 1 month); -- 获取下个月的第一天select DATEDIFF(date_add(curdate()-day(curdate())+1,interval 1 month ),DATE_ADD(curdate(),interval -day(curdate())+1 day)) from dual; --获取当前月的天数
-
PHP ==和=== // 首先定义两个变量$a = 1; // 整形$b = 1.0; //浮点//数组运算符$a === $b //全等 如果$a和$b具有相同的键／值对并且顺序和类型都相同则为 TRUE。 $a !== $b //不全等 如果$a不全等于$b则为 TRUE if($a === $b){echo '$a全等于$b';}else{echo "不全等";}if($a !== $b){echo '$a不全等于$b';}else{echo "全等";}关于PHP中“!==”与“!=”的区别主要是含义不同，两者具体的不同含义如下：1、!==意思是不全等于。打比方，$a = 2, $b="2" 那么，$a!==$b成立，但是$a!=$b不成立；用下面的代码测试：<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">无标题文档<?php $a = 2;$b="2";if($a!=$b) { echo "不等于";}if($a!==$b){ echo "绝对不等于";}?>2、!=意思是不等于，!=1就是不等于1的意思，！=是用中文输入法写的不等于，写程序时，最好不要使用中文输入法。指的是如果没有输入一个值赋给变量code。扩展资料：PHP中“!==”的含义与用法举例：非恒等于。 PHP中有等于和恒等于。0和false在C / C ++中相等，但在PHP中不完全相等。当使用两个等号时，以下表达式为真；0 ==假;1 ==真；'sdff'== true;但是，当使用3个等号时：0 ===假;1 ===真；'sdff'=== true;以上表达式都为假， 可以看出，当使用一致的符号时，诸如类型的因素也被判断。同理 0 !== false;为真。0 != false;为假。
-
-
0:00