flask_sqlalchemy常用查询语句总结

flask_sqlalchemy相关查询语句总结：

班级表：

学生表：

 

返回student表中所有数据并限制返回条数：select……from……limit()

result = db.session.query(Student.id,Student.name,Student.gender,Student.age,Student.classes).limit(10).all()

对应的SQL和结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes 
FROM student
LIMIT ? OFFSET ?

[(1, '张三', 'male', '18', 'java'), (2, '李四', 'female', '19', 'c++'), (3, '王五', 'male', '22', 'php'), (4, '赵六', 'female', '25', 'matalab'), (5, 'lee', 'man', '18', 'python'), (6, '张三', 'male', '18', 'java'), (7, '李四', 'female', '19', 'c++'), (8, '王五', 'male', '22', 'php'), (9, '赵六', 'female', '25', 'matalab'), (10, 'lee', 'man', '18', 'python')]

 

过滤条件查询： select……from……where ……and……

restult = db.session.query(Student.id,Student.name,Student.gender,Student.age,Student.classes).filter(Student.classes=='java').filter(Student.gender=='female')
print(restult)
print(result..all())

返回的SQL和对应的结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes 
FROM student 
WHERE student.classes = ? AND student.gender = ?

结果：[(11, '胡和', 'female', '18', 'java')]

 

过滤条件or_,and_ 的使用，需要先导入from sqlalchemy import or_,and_

task_filter = {
or_(
    and_(Student.gender=='female',
        Student.classes=='java'
        ),
    and_(
        Student.age == 18,
        Student.classes == 'python'
    )
)
}
restult2 = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).filter(*task_filter).all()
print(restult2)

返回的SQL和对应的结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes 
FROM student 
WHERE student.gender = ? AND student.classes = ? OR student.age = ? AND student.classes = ?

[(5, 'lee', 'male', '18', 'python'), 
(10, '乐奋', 'male', '18', 'python'), 
(11, '胡和', 'female', '18', 'java')]

上面这个filter中有两个条件组，关系为or，每个条件组里有一些and关系的条件。

 

两表联合查询：student表与grades表联合查询

restult3 = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes, Grades.grade).filter(
    Student.classes == 'java').filter(Student.gender == 'male').filter(Student.cls_id == Grades.id).all()

返回的SQL和对应的结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes, grades.grade AS grades_grade 
FROM student, grades 
WHERE student.classes = ? AND student.gender = ? AND student.cls_id = grades.id

[(6, '张三', 'male', '18', 'java', '一年级(3)班')]

 

Count函数使用：

task_filter={
    and_(Student.gender == 'male',
         Student.classes == 'python')
}
restult4 = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).filter(*task_filter).count()
print(restult4)

 返回的SQL和对应的结果：

SELECT
    count(*) AS count_1
FROM
    (
       select……from……where ……and……
        )
        AS anon_1

结果为：4

 

进行优化后的func.count()函数： 无子查询，效率高

restult5 = db.session.query(func.count(Student.id)).filter(*task_filter).scalar()
print(db.session.query(func.count(Student.id)).filter(*task_filter))
print(restult5)

 返回的SQL和对应的结果： 

select count(Student.id) as count_1
FROM
    student
WHERE
    student.gender = ? AND student.classes = ?

结果为：4

 

Join查询：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes, Grades.grade).join(Grades,Student.cls_id==Grades.id).filter(*task_filter).order_by(Student.id).limit(2)
print(query)
print(query.all())

返回的SQL和结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes, grades.grade AS grades_grade 
FROM student JOIN grades ON student.cls_id = grades.id 
WHERE student.gender = ? AND student.classes = ? ORDER BY student.id
 LIMIT ? OFFSET ?
[(6, '张三', 'male', '18', 'java', '一年级(3)班')]

 

with_entities()方法 指定某列并去重

#返回指定的一列
query1 = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).with_entities(Student.classes).distinct().all()
print(db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).with_entities(Student.classes).distinct())
print(query1)
#返回指定的两列
query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).with_entities(Student.classes,Student.cls_id).distinct().all()

返回对应的sql和查询结果：

SELECT DISTINCT student.classes AS student_classes 
FROM student
[('java',), ('c++',), ('php',), ('matalab',), ('python',), ('C',)]

with_entities()方法筛选字段：

query = Student.query.join(Grades,and_(Student.cls_id==Grades.id)).filter(Student.classes=='python').with_entities(Student.name,Grades.grade)
print(query)  #打印SQL
results = query.all()
print(results)  #打印结果
data = [dict(zip(result.keys(), result)) for result in results]
print(data) #将结果转为dict

对应结果如下：

SELECT student.name AS student_name, grades.grade AS grades_grade 
FROM student JOIN grades ON student.cls_id = grades.id 
WHERE student.classes = 'python'

[('乐奋', '一年级(5)班'), ('石雨', '一年级(5)班'), ('马庆', '一年级(1)班'), ('刘胜', '一年级(4)班')]

[{'name': '乐奋', 'grade': '一年级(5)班'}, {'name': '石雨', 'grade': '一年级(5)班'}, {'name': '马庆', 'grade': '一年级(1)班'}, {'name': '刘胜', 'grade': '一年级(4)班'}]

 

获取多个Model的记录：

除了筛选字段外，还可以用另一个方法获取多个 Model 的记录。那就是，返回两个 Model 的所有字段：

query = db.session.query(Student,Grades).join(Grades,and_(Student.cls_id==Grades.id)).filter(Student.classes=='python')
print(query)
restult = query.all()
print(restult)

返回的SQL和结果：

SELECT student.id AS student_id, student.name AS student_name, student.age AS student_age, student.gender AS student_gender, student.classes AS student_classes, student.cls_id AS student_cls_id, grades.id AS grades_id, grades.name AS grades_name, grades.grade AS grades_grade 
FROM student JOIN grades ON student.cls_id = grades.id 
WHERE student.classes = 'python'
[(, ), (, ), (, ), (, )]

使用上面的语法直接返回 Account 和 Bind 对象，可以进行更加灵活的操作。

 

group_by函数:

student = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).group_by("classes").all()  # 按照组
print(db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).group_by("classes"))
print(student)

对应的SQL和group_by查询结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes 
FROM student GROUP BY student.classes
[(18, '贾华', 'female', '19', 'C'), (12, '李天', 'male', '19', 'c++'), (11, '胡和', 'female', '18', 'java'), (14, '李广', 'male', '24', 'matalab'), (13, '陈安', 'male', '26', 'php'), (17, '刘胜', 'male', '25', 'python')]

 

倒序排序 order_by……desc：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).order_by(Student.age.desc())
print(query)
print(query.all())

对应的SQL和返回结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes 
FROM student ORDER BY student.age DESC
[(13, '陈安', 'male', '26', 'php'), (4, '赵六', 'female', '25', 'matalab'), (9, '赵六', 'female', '25', 'matalab'), (17, '刘胜', 'male', '25', 'python'), (14, '李广', 'male', '24', 'matalab'), (3, '王五', 'male', '22', 'php'), (8, '王五', 'male', '22', 'php'), (16, '马庆', 'male', '22', 'python'), (1, '张三', 'male', '20', 'java'), (2, '李四', 'female', '19', 'c++'), (7, '李四', 'female', '19', 'c++'), (12, '李天', 'male', '19', 'c++'), (18, '贾华', 'female', '19', 'C'), (5, 'lee', 'male', '18', 'python'), (6, '张三', 'male', '18', 'java'), (10, '乐奋', 'male', '18', 'python'), (11, '胡和', 'female', '18', 'java'), (15, '石雨', 'female', '17', 'python')]

 

按用户名模糊查询（两表联合查询名称 .like('%李%')）：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes,Grades.grade).join(Grades,Student.cls_id==Grades.id).filter(Student.name.like('%李%'))
print(query)
print(query.all())

非外键连接，表student与表grades内连接inner join

对应的SQL和返回结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes, grades.grade AS grades_grade 
FROM student JOIN grades ON student.cls_id = grades.id 
WHERE student.name LIKE "%李%"
[(7, '李四', 'female', '19', 'c++', '一年级(2)班'), (12, '李天', 'male', '19', 'c++', '一年级(2)班'), (14, '李广', 'male', '24', 'matalab', '一年级(3)班')]

还可以在 filter 得到结果后继续加 join 进行多表联查

 

outerjoin左外连接：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes,Grades.grade).outerjoin(Grades,Student.cls_id==Grades.id).filter(Student.name.like('%李%'))

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes, grades.grade AS grades_grade 
FROM student LEFT OUTER JOIN grades ON student.cls_id = grades.id 
WHERE student.name LIKE ?

[(2, '李四', 'female', '19', 'c++', None), (7, '李四', 'female', '19', 'c++', '一年级(2)班'), (12, '李天', 'male', '19', 'c++', '一年级(5)班'), (14, '李广', 'male', '24', 'matalab', '一年级(3)班')]

 

outerjoin相当于LEFT OUTER JOIN 左外连接；outerjoin( ) 返回结果有null

 

多表联合查询(没有外键)：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes,Grades.grade).join(Grades,and_(Student.cls_id==Grades.id,Student.classes=='python',Grades.grade=='一年级(5)班'))
print(query)
print(query.all())

 对应的SQL和返回结果：

SELECT student.id AS student_id, student.name AS student_name, student.gender AS student_gender, student.age AS student_age, student.classes AS student_classes, grades.grade AS grades_grade 
FROM student JOIN grades ON student.cls_id = grades.id 
AND student.classes = "python" 
AND grades.grade = "一年级(5)班"

[(10, '乐奋', 'male', '18', 'python', '一年级(5)班'), (15, '石雨', 'female', '17', 'python', '一年级(5)班')]

这里只有两张表，如果是三张表继续在后面join()即可。

要联结超过 2 张以上的表，可以直接在 join 得到的结果之后链式调用 join 。也可以在 filter 的结果后面链式调用 join 。join 和 filter 返回的都是 query 对象，因此可以无限链式调用下去。

 

外键是否设置中Join()函数的区别：

没有设置外键：

query = db.session.query(Student.id, Student.name, Student.gender, 
Student.age, Student.classes,Grades.grade)
.join(Grades,Student.cls_id==Grades.id)
.filter(Student.name.like('%李%'))

已经设置外键：

query = db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes,
Grades.grade)
.join(Grades)
.filter(Student.name.like('%李%'))

 

paginate()函数实现分页功能：

query =  db.session.query(Student).order_by(Student.age.desc()).paginate(1,5)
print(db.session.query(Student).order_by(Student.age.desc()))
print(query.items)
print(query.pages)
print(query.total)

对应SQL和结果：

SELECT student.id AS student_id, student.name AS student_name, student.age AS student_age, student.gender AS student_gender, student.classes AS student_classes, student.cls_id AS student_cls_id 
FROM student ORDER BY student.age DESC
[, , , , ]

这里的结果返回的是model对象，需要在query()括号里明确字段：

query =  db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).order_by(Student.age.desc()).paginate(1,5)
print(db.session.query(Student.id, Student.name, Student.gender, Student.age, Student.classes).order_by(Student.age.desc()))
print(query.items)

返回的是第一页前5个的结果：

[(13, '陈安', 'male', '26', 'php'), (4, '赵六', 'female', '25', 'matalab'), (9, '赵六', 'female', '25', 'matalab'), (17, '刘胜', 'male', '25', 'python'), (14, '李广', 'male', '24', 'matalab')]

 

in_、notin_函数：

query = db.session.query(Student.id, Student.name).filter(Student.id.in_([1,3,4]))
print(query.all())
query = db.session.query(Student.id, Student.name,Student.age).filter(Student.age.notin_([18, 19, 20,22]))
print(query.all())

返回结果：

[(1, '张三'), (3, '王五'), (4, '赵六')]
[(4, '赵六', '25'), (9, '赵六', '25'), (13, '陈安', '26'), (14, '李广', '24'), (15, '石雨', '17'), (17, '刘胜', '25')]

 

组合 union与union_all函数：

#组合 union与union_all函数 组合的字段数量应一致
query1 = db.session.query(Student.id, Student.name).filter(Student.age>22)
query2 = db.session.query(Grades.id,Grades.name).filter(Grades.id>1).distinct()
print(query1.union(query2))
print(query1.union(query2).all())  #union默认会去重
res = query1.union_all(query2).all()  #union_all默认不去重
print(res)

对应SQL和结果：

SELECT anon_1.student_id AS anon_1_student_id, anon_1.student_name AS anon_1_student_name 
FROM (SELECT student.id AS student_id, student.name AS student_name 
FROM student 
WHERE student.age > ? UNION SELECT grades.id AS grades_id, grades.name AS grades_name 
FROM grades 
WHERE grades.id > ?) AS anon_1
[(2, '李四'), (3, '王五'), (4, '赵六'), (5, 'lee'), (6, '张三'), (7, '李四'), (8, '王五'), (9, '赵六'), (10, 'lee'), (11, '张三'), (12, '李四'), (13, '王五'), (13, '陈安'), (14, '李广'), (14, '赵六'), (15, 'lee'), (16, '张三'), (17, '刘胜'), (17, '李四'), (18, '王五'), (19, '赵六'), (20, 'lee')]
[(4, '赵六'), (9, '赵六'), (13, '陈安'), (14, '李广'), (17, '刘胜'), (2, '李四'), (3, '王五'), (4, '赵六'), (5, 'lee'), (6, '张三'), (7, '李四'), (8, '王五'), (9, '赵六'), (10, 'lee'), (11, '张三'), (12, '李四'), (13, '王五'), (14, '赵六'), (15, 'lee'), (16, '张三'), (17, '李四'), (18, '王五'), (19, '赵六'), (20, 'lee')]

 

Group_by分组统计并排序

query = db.session.query(Student.classes,func.count(Student.name).label("cnt")).group_by('classes').order_by(desc('cnt'))
print(query) 
print(query.all())

返回的SQL和结果：

SELECT student.classes AS student_classes, count(student.name) AS cnt 
FROM student GROUP BY student.classes ORDER BY cnt DESC
[('python', 5), ('c++', 3), ('java', 3), ('matalab', 3), ('php', 3), ('C', 1)]

 

子查询：

query1 = db.session.query(Student,Grades).filter(Student.cls_id.in_(db.session.query(Grades.id).filter(Grades.grade=='一年级(5)班'))).with_entities(Student.id,Student.name,Student.age,Student.gender,Student.classes).distinct()
print(query1)
print(query1.all())

返回的SQL和结果：

SELECT DISTINCT student.id AS student_id, student.name AS student_name, student.age AS student_age, student.gender AS student_gender, student.classes AS student_classes 
FROM student 
WHERE student.cls_id IN (SELECT grades.id AS grades_id 
FROM grades 
WHERE grades.grade = '一年级(5)班')
[(10, '乐奋', '18', 'male', 'python'), (15, '石雨', '17', 'female', 'python')]

subquery = db.session.query(func.count(Student.id).label("sid")).filter(Student.cls_id==Grades.id).correlate(Grades).as_scalar()
#第一步：db.session.query(func.count(Student.id).label("sid")).filter(Student.cls_id==Grades.id)
#这句话SQL为：SELECT count(student.id) AS sid FROM student WHERE student.cls_id = grades.id    #如果直接运行，则会报错
#第二步：.correlate(Grades).as_scalar()   ==> 代表此时不执行查询操作，将其当作条件，在Grades表中查询时，才执行查询
restult = db.session.query(Grades.name, subquery)
#sql语句为：select Grades.name  subquery  from Grades
print(restult)
# 第三步：将subquery替换为上面的条件，则此句的SQL为：
# SELECT grades.name AS grades_name, (SELECT count(student.id) AS sid FROM student WHERE student.cls_id = grades.id) AS anon_1 FROM grades
print(restult.all())

 

动态组合条件。针对不同的场景，可能需要不同的查询条件，类似动态的拼接SQL 语句。

if filter_type == 1:
            search = and_(GameRoom.status ==1,or_(
                and_(GameRoom.white_user_id == user_id,
                     GameRoom.active_player == 1),
                and_(GameRoom.black_user_id == user_id,
                     GameRoom.active_player == 0)))
        elif filter_type == 2:
            search = and_(GameRoom.status ==1,or_(
                and_(GameRoom.white_user_id == user_id,
                     GameRoom.active_player == 0),
                and_(GameRoom.black_user_id == user_id,
                     GameRoom.active_player == 1)))
        elif filter_type == 3:
            search = GameRoom.create_by == user_id
        
        db.session.query(GameRoom).filter(search).all()

 

直接运行SQL语句查询：

如果查询实在太复杂，觉得用SQLAlchemy查询方式很难实现，或者要通过存储过程实现查询，可以让SQLAlchemy直接运行SQL语句返回结果。

sql ="""select b.user_id,b.user_name,b.icon,b.score,a.add_score from
            (select user_id, sum(score_new - score_old) as add_score from user_score_log
            where year(create_date)=year(now()) and month(create_date)=month(now())
            group by user_id) a join users b on a.user_id=b.user_id
            order by a.add_score desc limit 50"""
list_top = db.session.execute(sql).fetchall()

 

这些查询语句已经解决了大部分的需求。

注：一般写完查询后，应该打印生成的 SQL 语句查看一下有没有性能问题。

 

 

聚合函数：sum、max、min、avg、count

func.sum求和：
query = db.session.query(func.sum(Student.cls_id))

func.max求最大值：
query = db.session.query(func.max(Student.cls_id))

func.min求最小值：
query = db.session.query(func.min(Student.cls_id))

func.avg求平均值：
query = db.session.query(func.avg(Student.cls_id))

func.count进行统计：
query = db.session.query(func.count(Student.id))

filter常用过滤条件：==、！=、like(区分大小写，模糊查询)、ilike(不区分大小写)、in、not in、字段为空、不为空、and、or

from sqlalchemy import or_,and_,func,desc

query = db.session.query(Student.name).filter(Student.id == 6)

query = db.session.query(Student.id).filter(Student.id != 6)

query = db.session.query(Student.name).filter(Student.name.like('%王%'))

query = db.session.query(Student.id, Student.name).filter(Student.id.in_([1,3,4]))

query = db.session.query(Student.id, Student.name,Student.age).filter(Student.age.notin_([18, 19, 20,22]))

query = db.session.query(Student.name).filter(Student.cls_id==None)

query = db.session.query(Student.name).filter(Student.cls_id!=None)

query = db.session.query(Student.name).filter(and_(Student.age==18,Student.classes=='python'))

query = db.session.query(Student.name).filter(or_(Student.age==18,Student.classes=='python'))

print(query)   #打印SQL
print(query.all())   #打印结果

filter与filter_by的区别：

filter －》 column == expression
传入参数的写法，要用：类名.列名 两个等号 去判断
举例：
query(User.name).filter(User.fullname==’Ed Jones’)
且更复杂的查询的语法，比如_and()，or_()等多个条件的查询，只支持filter
举例：
query.filter(or_(User.name == ‘ed’, User.name == ‘wendy’))
query.filter(and_(User.name == ‘ed’, User.fullname == ‘Ed Jones’))

filter_by －》keyword = expression
传入参数的写法，只需要用：（不带类名的）列名 单个等号 就可以判断。
－》filter中，语法更加贴近于，类似于，Python的语法。
举例：
query(User.name).filter_by(fullname=’Ed Jones’)

filter_by() 只接受键值对参数，所以 filter_by() 不支持><（大于和小于）和 and_、or_查询。

在使用多条件匹配的时候，filter需要借助sqlalchemy里的and_ ，or_ ; 而filter_by不需要，直接把多个匹配条件写在一起。

group_by和having子句:

query = db.session.query(Student.age,func.count(Student.id)).group_by(Student.age).having(Student.age > 20)
print(query)
print(query.all())

对应的SQL和结果：

SELECT student.age AS student_age, count(student.id) AS count_1 
FROM student GROUP BY student.age 
HAVING student.age > ?
[('22', 3), ('24', 1), ('25', 3), ('26', 1)]

 

参考链接：https://blog.zengrong.net/post/join-in-flash-sqlalchemy/

https://www.cnblogs.com/huchong/p/8274510.html#_label3_1_1_0

https://www.cnblogs.com/zhongyehai/p/11828337.html