SQL查询(提高版--1)
2019-08-11 09:19
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表名和字段
准备工作:
表设计:
–1.学生表
Student(s_id,s_name,s_birth,s_sex) –学生编号,学生姓名, 出生年月,学生性别
–2.课程表
Course(c_id,c_name,t_id) – –课程编号, 课程名称, 教师编号
–3.教师表
Teacher(t_id,t_name) –教师编号,教师姓名
–4.成绩表
Score(s_id,c_id,s_score) –学生编号,课程编号,分数
建表语句:
[code] --建库 create database querySql; use querySql; --建表 --学生表 CREATE TABLE `Student`( `s_id` VARCHAR(20), `s_name` VARCHAR(20) NOT NULL DEFAULT '', `s_birth` VARCHAR(20) NOT NULL DEFAULT '', `s_sex` VARCHAR(10) NOT NULL DEFAULT '', PRIMARY KEY(`s_id`) ); --课程表 CREATE TABLE `Course`( `c_id` VARCHAR(20), `c_name` VARCHAR(20) NOT NULL DEFAULT '', `t_id` VARCHAR(20) NOT NULL, PRIMARY KEY(`c_id`) ); --教师表 CREATE TABLE `Teacher`( `t_id` VARCHAR(20), `t_name` VARCHAR(20) NOT NULL DEFAULT '', PRIMARY KEY(`t_id`) ); --成绩表 CREATE TABLE `Score`( `s_id` VARCHAR(20), `c_id` VARCHAR(20), `s_score` INT(3), PRIMARY KEY(`s_id`,`c_id`) );
数据插入:
[code]--插入学生表测试数据 insert into Student values('01' , '赵雷' , '1990-01-01' , '男'); insert into Student values('02' , '钱电' , '1990-12-21' , '男'); insert into Student values('03' , '孙风' , '1990-05-20' , '男'); insert into Student values('04' , '李云' , '1990-08-06' , '男'); insert into Student values('05' , '周梅' , '1991-12-01' , '女'); insert into Student values('06' , '吴兰' , '1992-03-01' , '女'); insert into Student values('07' , '郑竹' , '1989-07-01' , '女'); insert into Student values('08' , '王菊' , '1990-01-20' , '女'); --课程表测试数据 insert into Course values('01' , '语文' , '02'); insert into Course values('02' , '数学' , '01'); insert into Course values('03' , '英语' , '03'); --教师表测试数据 insert into Teacher values('01' , '张三'); insert into Teacher values('02' , '李四'); insert into Teacher values('03' , '王五'); --成绩表测试数据 insert into Score values('01' , '01' , 80); insert into Score values('01' , '02' , 90); insert into Score values('01' , '03' , 99); insert into Score values('02' , '01' , 70); insert into Score values('02' , '02' , 60); insert into Score values('02' , '03' , 80); insert into Score values('03' , '01' , 80); insert into Score values('03' , '02' , 80); insert into Score values('03' , '03' , 80); insert into Score values('04' , '01' , 50); insert into Score values('04' , '02' , 30); insert into Score values('04' , '03' , 20); insert into Score values('05' , '01' , 76); insert into Score values('05' , '02' , 87); insert into Score values('06' , '01' , 31); insert into Score values('06' , '03' , 34); insert into Score values('07' , '02' , 89); insert into Score values('07' , '03' , 98);
结果图如下:
数据查询:
[code]-- 1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数 select a.* ,b.s_score as 01_score,c.s_score as 02_score from student a join score b on a.s_id=b.s_id and b.c_id='01' left join score c on a.s_id=c.s_id and c.c_id='02' or c.c_id = NULL where b.s_score>c.s_score -- 2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数 select a.* ,b.s_score as 01_score,c.s_score as 02_score from student a left join score b on a.s_id=b.s_id and b.c_id='01' or b.c_id=NULL join score c on a.s_id=c.s_id and c.c_id='02' where b.s_score<c.s_score -- 3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩 select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from student b join score a on b.s_id = a.s_id GROUP BY b.s_id,b.s_name HAVING ROUND(AVG(a.s_score),2)>=60; -- 4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩 -- (包括有成绩的和无成绩的) select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score from student b left join score a on b.s_id = a.s_id GROUP BY b.s_id,b.s_name HAVING ROUND(AVG(a.s_score),2)<60 union select a.s_id,a.s_name,0 as avg_score from student a where a.s_id not in ( select distinct s_id from score); -- 5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩 select a.s_id,a.s_name,count(b.c_id) as sum_course,sum(b.s_score) as sum_score from student a left join score b on a.s_id=b.s_id GROUP BY a.s_id,a.s_name; -- 6、查询"李"姓老师的数量 select count(t_id) from teacher where t_name like '李%'; -- 7、查询学过"张三"老师授课的同学的信息 select a.* from student a join score b on a.s_id=b.s_id where b.c_id in( select c_id from course where t_id =( select t_id from teacher where t_name = '张三')); -- 8、查询没学过"张三"老师授课的同学的信息 select * from student c where c.s_id not in( select a.s_id from student a join score b on a.s_id=b.s_id where b.c_id in( select c_id from course where t_id =( select t_id from teacher where t_name = '张三'))); -- 9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息(好题) select a.* from student a,score b,score c where a.s_id = b.s_id and a.s_id = c.s_id and b.c_id='01' and c.c_id='02'; -- 10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息 select a.* from student a where a.s_id in (select s_id from score where c_id='01' ) and a.s_id not in(select s_id from score where c_id='02') -- 11、查询没有学全所有课程的同学的信息 select s.* from student s where s.s_id in( select s_id from score where s_id not in( select a.s_id from score a join score b on a.s_id = b.s_id and b.c_id='02' join score c on a.s_id = c.s_id and c.c_id='03' where a.c_id='01')) -- 12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息 select * from student where s_id in( select distinct a.s_id from score a where a.c_id in(select a.c_id from score a where a.s_id='01') ); -- 13、查询和"01"号的同学学习的课程完全相同的其他同学的信息 select a.* from student a where a.s_id in( select distinct s_id from score where s_id!='01' and c_id in(select c_id from score where s_id='01') group by s_id having count(1)=(select count(1) from score where s_id='01')); -- 14、查询没学过"张三"老师讲授的任一门课程的学生姓名 select a.s_name from student a where a.s_id not in ( select s_id from score where c_id = (select c_id from course where t_id =( select t_id from teacher where t_name = '张三')) group by s_id); -- 15、查询两门及其以上不及格课程的同学的学号,姓名及其平均成绩 select a.s_id,a.s_name,ROUND(AVG(b.s_score)) from student a left join score b on a.s_id = b.s_id where a.s_id in( select s_id from score where s_score<60 GROUP BY s_id having count(1)>=2) GROUP BY a.s_id,a.s_name -- 16、检索"01"课程分数小于60,按分数降序排列的学生信息 select a.*,b.c_id,b.s_score from student a,score b where a.s_id = b.s_id and b.c_id='01' and b.s_score<60 ORDER BY b.s_score DESC; -- 17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩 select a.s_id,(select s_score from score where s_id=a.s_id and c_id='01') as 语文, (select s_score from score where s_id=a.s_id and c_id='02') as 数学, (select s_score from score where s_id=a.s_id and c_id='03') as 英语, round(avg(s_score),2) as 平均分 from score a GROUP BY a.s_id ORDER BY 平均分 DESC; -- 18.查询各科成绩最高分、最低分和平均分:以如下形式显示:课程ID,课程name,最高分,最低分,平均分,及格率,中等率,优良率,优秀率 --及格为>=60,中等为:70-80,优良为:80-90,优秀为:>=90 select a.c_id,b.c_name,MAX(s_score),MIN(s_score),ROUND(AVG(s_score),2), ROUND(100*(SUM(case when a.s_score>=60 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 及格率, ROUND(100*(SUM(case when a.s_score>=70 and a.s_score<=80 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 中等率, ROUND(100*(SUM(case when a.s_score>=80 and a.s_score<=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优良率, ROUND(100*(SUM(case when a.s_score>=90 then 1 else 0 end)/SUM(case when a.s_score then 1 else 0 end)),2) as 优秀率 from score a left join course b on a.c_id = b.c_id GROUP BY a.c_id,b.c_name 分析:ROUND() 函数 ROUND 函数用于把数值字段舍入为指定的小数位数。 SQL ROUND() 语法 SELECT ROUND(column_name,decimals) FROM table_name -- 19、按各科成绩进行排序,并显示排名(实现不完全) -- mysql没有rank函数 select a.s_id,a.c_id, @i:=@i +1 as i保留排名, @k:=(case when @score=a.s_score then @k else @i end) as rank不保留排名, @score:=a.s_score as score from ( select s_id,c_id,s_score from score WHERE c_id='01' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC )a,(select @k:=0,@i:=0,@score:=0)s union select a.s_id,a.c_id, @i:=@i +1 as i, @k:=(case when @score=a.s_score then @k else @i end) as rank, @score:=a.s_score as score from ( select s_id,c_id,s_score from score WHERE c_id='02' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC )a,(select @k:=0,@i:=0,@score:=0)s union select a.s_id,a.c_id, @i:=@i +1 as i, @k:=(case when @score=a.s_score then @k else @i end) as rank, @score:=a.s_score as score from ( select s_id,c_id,s_score from score WHERE c_id='03' GROUP BY s_id,c_id,s_score ORDER BY s_score DESC )a,(select @k:=0,@i:=0,@score:=0)s -- 20、查询学生的总成绩并进行排名 select a.s_id, @i:=@i+1 as i, @k:=(case when @score=a.sum_score then @k else @i end) as rank, @score:=a.sum_score as score from (select s_id,SUM(s_score) as sum_score from score GROUP BY s_id ORDER BY sum_score DESC)a, (select @k:=0,@i:=0,@score:=0)s -- 21、查询不同老师所教不同课程平均分从高到低显示 (为啥avg的参数b.s_score?) select a.t_id,c.t_name,a.c_id,ROUND(avg(s_score),2) as avg_score from course a left join score b on a.c_id=b.c_id left join teacher c on a.t_id=c.t_id GROUP BY a.c_id,a.t_id,c.t_name ORDER BY avg_score DESC; -- 22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩 select d.*,c.排名,c.s_score,c.c_id from ( select a.s_id,a.s_score,a.c_id,@i:=@i+1 as 排名 from score a,(select @i:=0)s where a.c_id='01' )c left join student d on c.s_id=d.s_id where 排名 BETWEEN 2 AND 3 UNION select d.*,c.排名,c.s_score,c.c_id from ( select a.s_id,a.s_score,a.c_id,@j:=@j+1 as 排名 from score a,(select @j:=0)s where a.c_id='02' )c left join student d on c.s_id=d.s_id where 排名 BETWEEN 2 AND 3 UNION select d.*,c.排名,c.s_score,c.c_id from ( select a.s_id,a.s_score,a.c_id,@k:=@k+1 as 排名 from score a,(select @k:=0)s where a.c_id='03' )c left join student d on c.s_id=d.s_id where 排名 BETWEEN 2 AND 3; -- 23、统计各科成绩各分数段人数:课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比 select distinct f.c_name,a.c_id,b.`85-100`,b.百分比,c.`70-85`,c.百分比,d.`60-70`,d.百分比,e.`0-60`,e.百分比 from score a left join (select c_id,SUM(case when s_score >85 and s_score <=100 then 1 else 0 end) as `85-100`, ROUND(100*(SUM(case when s_score >85 and s_score <=100 then 1 else 0 end)/count(*)),2) as 百分比 from score GROUP BY c_id)b on a.c_id=b.c_id left join (select c_id,SUM(case when s_score >70 and s_score <=85 then 1 else 0 end) as `70-85`, ROUND(100*(SUM(case when s_score >70 and s_score <=85 then 1 else 0 end)/count(*)),2) as 百分比 from score GROUP BY c_id)c on a.c_id=c.c_id left join (select c_id,SUM(case when s_score >60 and s_score <=70 then 1 else 0 end) as `60-70`, ROUND(100*(SUM(case when s_score >60 and s_score <=70 then 1 else 0 end)/count(*)),2) as 百分比 from score GROUP BY c_id)d on a.c_id=d.c_id left join (select c_id,SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end) as `0-60`, ROUND(100*(SUM(case when s_score >=0 and s_score <=60 then 1 else 0 end)/count(*)),2) as 百分比 from score GROUP BY c_id)e on a.c_id=e.c_id left join course f on a.c_id = f.c_id -- 24、查询学生平均成绩及其名次 select a.s_id, @i:=@i+1 as '不保留空缺排名', @k:=(case when @avg_score=a.avg_s then @k else @i end) as '保留空缺排名', @avg_score:=avg_s as '平均分' from (select s_id,ROUND(AVG(s_score),2) as avg_s from score GROUP BY s_id)a,(select @avg_score:=0,@i:=0,@k:=0)b; 分析: 《select sid,ROUND(AVG(score),2) as avg_s from SC GROUP BY sid)a:根据sid算出score列的平均数,保留两位小数,结果起名a; (select @avg_score:=0,@i:=0,@k:=0)b:定义@avg_score,@i,@k三个标量,初始值=0,起名b,@avg_score是保存avg_s的值,@i,@k是排序的序列值(第一名,第二名这类) @i:=@i+1 as '不保留空缺排名':执行时@i的值在上一次基础上加1,初始值0,第一行@i=1,第二行@i=2,以此类推,这一列的名字起名'不保留空缺排名',也就是'按照成绩排序,成绩相同的排在后面一位’ @k:=(case when @avg_score=a.avg_s then @k else @i end) as '保留空缺排名':判断@avg_score和a.avg_s相不相等,@avg_score初始值0,第一行是0,第二行的值是第一行avg_s的值,也就是说判断下一个sid的成绩和上一个相不相等,要是相等返回@k,不相等返回@i,@k的值初始值是0,要是 @avg_score和a.avg_s不相等,@k的值就是@i的值,要是 @avg_score和a.avg_s相等,@k的值就是上一行的@i,结果起名'保留空缺排名',也就是‘成绩相同排名并列’ 总结来说就是根据平均分产生不并列排名的成绩和并列排名的成绩,》 -- 25、查询各科成绩前三名的记录 -- 1.选出b表比a表成绩大的所有组 -- 2.选出比当前id成绩大的 小于三个的 select a.s_id,a.c_id,a.s_score from score a left join score b on a.c_id = b.c_id and a.s_score<b.s_score group by a.s_id,a.c_id,a.s_score HAVING COUNT(b.s_id)<3 ORDER BY a.c_id,a.s_score DESC -- 26、查询每门课程被选修的学生数 select c_id,count(s_id) from score a GROUP BY c_id -- 27、查询出只有两门课程的全部学生的学号和姓名 (多练) select s_id,s_name from student where s_id in( select s_id from score GROUP BY s_id HAVING COUNT(c_id)=2); -- 28、查询男生、女生人数 select s_sex,COUNT(s_sex) as 人数 from student GROUP BY s_sex -- 29、查询名字中含有"风"字的学生信息 select * from student where s_name like '%风%'; -- 30、查询同名同性学生名单,并统计同名人数 select a.s_name,a.s_sex,count(*) from student a JOIN student b on a.s_id !=b.s_id and a.s_name = b.s_name and a.s_sex = b.s_sex GROUP BY a.s_name,a.s_sex -- 31、查询1990年出生的学生名单 select s_name from student where s_birth like '1990%' -- 32、查询每门课程的平均成绩,结果按平均成绩降序排列,平均成绩相同时,按课程编号升序排列 select c_id,ROUND(AVG(s_score),2) as avg_score from score GROUP BY c_id ORDER BY avg_score DESC,c_id ASC -- 33、查询平均成绩大于等于85的所有学生的学号、姓名和平均成绩 select a.s_id,b.s_name,ROUND(avg(a.s_score),2) as avg_score from score a left join student b on a.s_id=b.s_id GROUP BY s_id HAVING avg_score>=85 -- 34、查询课程名称为"数学",且分数低于60的学生姓名和分数 select a.s_name,b.s_score from score b LEFT JOIN student a on a.s_id=b.s_id where b.c_id=( select c_id from course where c_name ='数学') and b.s_score<60 思考:什么时候用GROUP BY ? -- 35、查询所有学生的课程及分数情况; select a.s_id,a.s_name, SUM(case c.c_name when '语文' then b.s_score else 0 end) as '语文', SUM(case c.c_name when '数学' then b.s_score else 0 end) as '数学', SUM(case c.c_name when '英语' then b.s_score else 0 end) as '英语', SUM(b.s_score) as '总分' from student a left join score b on a.s_id = b.s_id left join course c on b.c_id = c.c_id GROUP BY a.s_id,a.s_name 《《《 分析:Case具有两种格式。简单Case函数和Case搜索函数。 --简单Case函数 CASE sex WHEN '1' THEN '男' WHEN '2' THEN '女' ELSE '其他' END --Case搜索函数 CASE WHEN sex = '1' THEN '男' WHEN sex = '2' THEN '女' ELSE '其他' END》》》 -- 36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数; select a.s_name,b.c_name,c.s_score from course b left join score c on b.c_id = c.c_id left join student a on a.s_id=c.s_id where c.s_score>=70 -- 37、查询不及格的课程 select a.s_id,a.c_id,b.c_name,a.s_score from score a left join course b on a.c_id = b.c_id where a.s_score<60 --38、查询课程编号为01且课程成绩在80分以上的学生的学号和姓名; select a.s_id,b.s_name from score a LEFT JOIN student b on a.s_id = b.s_id where a.c_id = '01' and a.s_score>80 -- 39、求每门课程的学生人数 select count(*) from score GROUP BY c_id; -- 40、查询选修"张三"老师所授课程的学生中,成绩最高的学生信息及其成绩 -- 查询老师id select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='张三' -- 查询最高分(可能有相同分数) select MAX(s_score) from score where c_id='02' -- 查询信息(综合以上两条) select a.*,b.s_score,b.c_id,c.c_name from student a LEFT JOIN score b on a.s_id = b.s_id LEFT JOIN course c on b.c_id=c.c_id where b.c_id =(select c_id from course c,teacher d where c.t_id=d.t_id and d.t_name='张三') and b.s_score in (select MAX(s_score) from score where c_id='02') -- 41、查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩 select DISTINCT b.s_id,b.c_id,b.s_score from score a,score b where a.c_id != b.c_id and a.s_score = b.s_score -- 42、查询每门功课成绩最好的前两名(不懂) -- 牛逼的写法 select a.s_id,a.c_id,a.s_score from score a where (select COUNT(1) from score b where b.c_id=a.c_id and b.s_score>=a.s_score)<=2 ORDER BY a.c_id -- 43、统计每门课程的学生选修人数(超过5人的课程才统计)。要求输出课程号和选修人数,查询结果按人数降序排列,若人数相同,按课程号升序排列 select c_id,count(*) as total from score GROUP BY c_id HAVING total>5 ORDER BY total,c_id ASC -- 44、检索至少选修两门课程的学生学号 select s_id,count(*) as sel from score GROUP BY s_id HAVING sel>=2 -- 45、查询选修了全部课程的学生信息 select * from student where s_id in( select s_id from score GROUP BY s_id HAVING count(*)=(select count(*) from course)) --46、查询各学生的年龄 -- 按照出生日期来算,当前月日 < 出生年月的月日则,年龄减一 select s_birth,(DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(s_birth,'%Y') - (case when DATE_FORMAT(NOW(),'%m%d')>DATE_FORMAT(s_birth,'%m%d') then 0 else 1 end)) as age from student; -- 47、查询本周过生日的学生 select * from student where WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))=WEEK(s_birth) select * from student where YEARWEEK(s_birth)=YEARWEEK(DATE_FORMAT(NOW(),'%Y%m%d')) select WEEK(DATE_FORMAT(NOW(),'%Y%m%d')) -- 48、查询下周过生日的学生 select * from student where WEEK(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =WEEK(s_birth) -- 49、查询本月过生日的学生 select * from student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d')) =MONTH(s_birth) -- 50、查询下月过生日的学生 select * from student where MONTH(DATE_FORMAT(NOW(),'%Y%m%d'))+1 =MONTH(s_birth) -- 51.扩展这里着重介绍Not Exists(Exists用法类似),Not Exists 不存在 用法:Select * from TableA a where Not Exists (Select * from TableB b where a.id=b.id and a.name=b.name); 1、Not Exists 用在where之后,且后面紧跟子查询语句(带括号); 2、Not Exists(Exists) 并不关心子查询的结果具体是什么,只关心子查询有没有结果; 3、这条语句的意思,把TableA的记录逐条代入到子查询,如果子查询结果集为空,说明不存在,那么这条TableA的记录出现在最终结果集,否则被排除; 用法:Select * from TableA a where Not Exists (Select 1 from TableB); -- 用left join查询不在黑名单里边用户信息 SELECT a.uid,a.name FROM USER a LEFT JOIN banuser b ON a.uid=b.uid WHERE a.uid NOT IN(SELECT b.uid FROM banuser WHERE a.uid=b.uid) -- 用NOT EXISTS 方式查询不在黑名单里边用户信息 SELECT a.uid,a.name FROM USER a WHERE uid NOT EXISTS(SELECT uid FROM banuser ) 有问题-- -- 面试题 CREATE TABLE Course_score( id VARCHAR(15), name VARCHAR(20), course VARCHAR(20), c_score DOUBLE(5,2), t_term VARCHAR(20) ); INSERT INTO Course_score VALUES('1','张三','数学',80,'2015'); INSERT INTO Course_score VALUES('2','李四','语文',90,'2016'); INSERT INTO Course_score VALUES('3','王五','化学',70,'2017'); INSERT INTO Course_score VALUES('4','张三','语文',80,'2015'); INSERT INTO Course_score VALUES('5','张三','化学',90,'2015'); -- 51 查出每个学期每门课程分最高分记录(结果集包含全部5个字段) SELECT c.* FROM (SELECT t_term term,course course,MAX(c_score) mscore FROM course_score GROUP BY t_term,course) maxsc LEFT JOIN course_score c ON maxsc.course = c.`course` AND maxsc.term = c.`t_term` AND maxsc.mscore = c.`c_score` ORDER BY c.t_term asc -- 第二种方法 SELECT a.*,MAX(a.c_score)AS max_score FROM course_score a LEFT JOIN course_score b ON a.course=b.course AND a.t_term = b.t_term GROUP BY a.t_term,a.course ORDER BY b.t_term ASC -- 52 HAVING和group搭配使用(新的表见网址https://www.jianshu.com/p/8b135d373df1) 当然提到GROUP BY 我们就不得不提到HAVING,HAVING相当于条件筛选,但它与WHERE筛选不同,HAVING是对于GROUP BY对象进行筛选。 我们举个例子: 每个部门人数都有了,那如果我们想要进一步知道员工人数大于30000的部门是哪些,这个时候就得用到HAVING了。 语句如下: SELECT ( SELECT d.dept_name FROM departments d WHERE de.dept_no = d.dept_no ) AS 部门, count( de.emp_no ) AS 人数 FROM dept_emp de WHERE de.to_date = '9999-01-01' GROUP BY de.dept_no HAVING count( de.emp_no ) > 30000
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