sql统计不为空的字段数_SQL查询技巧汇总-基本常⽤查询学习SQL不简单，SQL中最难的当然是查询，⼀个⼩⼩的select，能把⼈玩死，下⾯是整理的SQL查询技巧，好好品品！
select
select * from student;
all 查询所有
select all sex from student;
sql自学难吗distinct 过滤重复
select distinct sex from student;
count 统计
select count(*) from student;
select count(sex) from student;
select count(distinct sex) from student;
top 取前N条记录
select top 3 * from student;
alias column name 列重命名
select id as 编号, name ‘名称’, sex 性别 from student;
alias table name 表重命名
select id, name, s.id, s.name from student s;
column 列运算
select (age + id) col from student;
select s.name + ‘-’ + c.name from classes c, student s where s.cid = c.id;
where 条件
select * from student where id = 2;
select * from student where id > 7;
select * from student where id < 3;
select * from student where id <> 3;
select * from student where id >= 3;
select * from student where id <= 5;
select * from student where id !> 3;
select * from student where id !< 5;
and 并且
select * from student where id > 2 and sex = 1;
or 或者
select * from student where id = 2 or sex = 1;
between … and … 相当于并且
select * from student where id between 2 and 5;
select * from student where id not between 2 and 5;
like 模糊查询
select * from student where name like ‘%a%’;
select * from student where name like ‘%[a][o]%’;
select * from student where name not like ‘%a%’;
select * from student where name like ‘ja%’;
select * from student where name not like ‘%[j,n]%’;
select * from student where name like ‘%[j,n,a]%’;
select * from student where name like ‘%[^ja,as,on]%’;
select * from student where name like ‘%[ja_on]%’;
in ⼦查询
select * from student where id in (1, 2);
not in 不在其中
select * from student where id not in (1, 2);
is null 是空
select * from student where age is null;
is not null 不为空
select * from student where age is not null;
order by 排序
select * from student order by name;
select * from student order by name desc;
select * from student order by name asc;
group by 分组
按照年龄进⾏分组统计
select count(age), age from student group by age;
按照性别进⾏分组统计
select count(*), sex from student group by sex;
按照年龄和性别组合分组统计，并排序
select count(*), sex from student group by sex, age order by age;
按照性别分组，并且是id⼤于2的记录最后按照性别排序
select count(*), sex from student where id > 2 group by sex order by sex;
查询id⼤于2的数据，并完成运算后的结果进⾏分组和排序
select count(), (sex id) new from student where id > 2 group by sex * id order by sex * id; group by all 所有分组
按照年龄分组，是所有的年龄
select count(*), age from student group by all age;
having 分组过滤条件
按照年龄分组，过滤年龄为空的数据，并且统计分组的条数和现实年龄信息
select count(*), age from student group by age having age is not null;
按照年龄和cid组合分组，过滤条件是cid⼤于1的记录
select count(*), cid, sex from student group by cid, sex having cid > 1;
按照年龄分组，过滤条件是分组后的记录条数⼤于等于2
select count(*), age from student group by age having count(age) >= 2;
按照cid和性别组合分组，过滤条件是cid⼤于1，cid的最⼤值⼤于2
select count(*), cid, sex from student group by cid, sex having cid > 1 and max(cid) > 2;

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