postgresql表操作

postgresql数据库操作

    • 1.表基本操作
      • 1.1创建表
      • 1.2 查看表
      • 1.3清空表数据
      • 1.4删除表
      • 1.5退出数据库
    • 2.表属性操作
      • 2.1增加列
      • 2.2删除列
      • 2.3修改列属性
      • 2.4增加列非空约束
      • 2.5 增加列唯一约束
      • 2.6删除主键约束
      • 2.7创建主键约束
    • 3.表数据操作
      • 3.1数据查询
      • 3.2数据条件查询【where】
      • 3.3数据表达式查询
      • 3.4函数查询
      • 3.5分组
      • 3.6 映射【根据条件添加列,聚合操作】
      • 3.7 排序(order by)
      • 3.8 左右连表【多表查询】
      • 3.9 联合【union】
      • 3.10 数据增删改
    • 4.表关系
      • 4.1 一对多【设置一个外键】
      • 4.2 多对多【设置多个外键】

1.表基本操作

1.1创建表

create table tb4(
	id BIGSERIAL not null primary key,-- 不允许为空,&主键&自增
    name varchar(16) not null, --允许为空
    email varchar(32) null, -- 可以为空(默认)
    age int default 3  -- 插入数据,不给值,默认值为3
);

1.2 查看表

  • 查看所有表
    \d
    
  • 查看表信息
    -- \d 表名
    \d flow
    

1.3清空表数据

TRUNCATE TABLE flow;

1.4删除表

DROP TABLE flow;

1.5退出数据库

\q

2.表属性操作

2.1增加列

ALTER TABLE flow ADD age int;

2.2删除列

ALTER TABLE flow DROP COLUMN age;

2.3修改列属性

ALTER TABLE flow ALTER COLUMN date TYPE varchar;
Alter TABLE point alter column point  TYPE geometry USING point ::geometry;
select st_astext(geo) from test;

2.4增加列非空约束

alter table flow alter column age set not null;

2.5 增加列唯一约束

ALTER TABLE flow ADD CONSTRAINT FlowUniqueConstraint UNIQUE(age);
-- 删除约束
ALTER TABLE flow DROP CONSTRAINT FlowUniqueConstraint ;

2.6删除主键约束

\d flow; # 查看主键的名称
ALTER TABLE flow DROP CONSTRAINT flow_pkey;

2.7创建主键约束

ALTER TABLE flow ADD CONSTRAINT FlowPrimaryKey PRIMARY KEY (ID);
-- 删除主键约束
ALTER TABLE flow DROP CONSTRAINT FlowPrimaryKey ;

3.表数据操作

3.1数据查询

  • 查询表所有数据
    select * from flow;
    
  • 查询表前100条数据
    SELECT * FROM flow ORDER BY id ASC LIMIT 100;
    
  • 查询表后100条数据
    SELECT * FROM flow ORDER BY id DESC LIMIT 100;
    
  • 查询表某几列数据
    SELECT id,date FROM flow;
    -- 修改列名称
    SELECT id as n1,date as n2 FROM flow;
    

3.2数据条件查询【where】

  • >

    -- 查找年龄大于30
    select * from info where age>30;
    -- 查找id大于1
    select * from info where id>1;
    
  • =

    -- 查找id等于1
    select * from info where id=1;
    
  • >=

    -- 查找id大于等于1
    select * from info where id>=1;
    
  • !=

    -- 查找id不等于1
    select * from info where id!=1;
    
  • between and

    -- 查找2<=id<=4
    select * from info where id between 2 and 4;
    
  • and

    -- 查找name="wxy" 并且 age=19
    select * from info where name="wxy" and age=19;
    
  • or

    -- 查找name="wxy" 或者 age=49
    select * from info where name="wxy" or age=49;
    -- 查找name="wxy" 或者 email="[email protected]" 里面 age=49
    select * from info where (name="wxy" or email="[email protected]") and age=49;
    
  • in

    -- 查找id 等于1或4或6
    select * from info where id in (1,4,6);
    -- 查找id 在depart表中存在的id
    select * from info where id in (select id from depart);
    
  • not in

    -- 查找id不等于1或4或6
    select * from info where id not in (1,4,6);
    
  • exists

    -- 查找是否有select * from depart where id=5,如果有,就查询select * from info
    select * from info where exists(select * from depart where id=5);
    
  • not exists

    -- 查找是否有select * from depart where id=5,如果没有,就查询select * from info
    select * from info where not exists(select * from depart where id=5);
    
  • 子查询

    -- 查找id>2 里面的age>10的信息
    select * from (select * from info where id>2) as T where age>10;
    
  • is

    -- 查询非空数据
    SELECT * FROM flow WHERE "to" is not null;
    
  • limit

    -- 取前五条
    select * from info limit 5;
    
  • limit offset

    -- 从第二个位置开始取,取三个,offset从0开始
    select * from info limit 3 offset 2;
    

3.3数据表达式查询

  • where

    SELECT * FROM flow WHERE "from" = 1000;
    
  • like用于模糊查询

    • %【匹配表示0到多个】

      select * from info where name like '%wxy';
      
    • _【匹配一个】

      select * from info where name like "_wxy";
      

3.4函数查询

  • count
    -- 查询数据条数
    SELECT COUNT(*) AS "flow" FROM flow;
    
  • sum
    SELECT sum("from") AS "flow" FROM flow;
    
    
  • max
    SELECT max("from") FROM flow;
    
  • min
    SELECT min("from") FROM flow;
    
  • DISTINCT 【过滤重复值】
    SELECT DISTINCT id FROM depart;
    

3.5分组

  • group by

    select age,max(id),min(id),count(id),sum(id),avg(id) from info group by age;
    select age,count(1) from info group by age;
    select depart_id,count(id) from info group by depart_id;
    
  • having【先执行分组再判断条件】

    select depart_id,count(id) from info group by depart_id having count(id)>2;
    
    select age,max(id) from info group by age;
    -- 只获取根据年龄分组的获取最大的id
    select * from info where id in (select max(id) from info group by age);
    
    -- 根据age分组,再查找count(id)>2 
    select age,count(id) from info group by age having count(id)>2;
    -- 聚合条件,having放后面
    select age,count(id) from info where id>4 group by age having count(id)>2;
    
    select age,
    count(id)
    from info where id>2 group by age having count(id)>1 order by age desc limit 1;
    - 要查询的表info
    - 条件 id>2
    - 根据age分组
    - 对分组后的数据再根据聚合条件过滤 count(id)>1
    - 根据age从大到小排序
    - 获取第1

3.6 映射【根据条件添加列,聚合操作】

  • 获取自己想要的列

    • 获取想要的数据列
      -- 只获取id,name两列
      select id,name from info;
      -- 将name列起别名为n
      select id,name as n from info;
      -- 增加一列123,所有值都为123
      select id,name as n,123 from info;
    
    -- 查找id,name,添加num列值为666,
    -- 添加mid列值为depart表中id的最大值,
    -- 添加nid列值为depart表中id的最小值
    select id,
    name,
    666 as num,
    (select max(id) from depart) as mid,
    (select min(id) from depart) as nid,
    age 
    from info;
    
    -- 查找id,name,添加一列x1,info中的depart_id=depart中的id为条件,找depart表中的title作为x1的值
    
    select id ,
    name,
    (select title from depart where depart.id=info.depart_id) as x1
    from info;
    
    select 
    id ,
    name,
    (select title from depart where depart.id=info.depart_id) as x1,
    (select title from depart where depart.id=info.id) as x2 
    from info;
    
  • case when then end

    -- 添加一列为v1,当depart_id=1时,将v1的值赋值为 "第1部门" 
       select id,
        name,
        case depart_id when 1 then '第1部门' end v1
        from info;
    
  • case when then else end

    -- 添加一列为v2,当depart_id=1时,将v2的值赋值为 "第1部门" ,否则赋值为 "其他"
    select 
    id,
    name,
    case depart_id when 1 then '第1部门' else '其他' end v2 
    from info;
    
  • case when then ... when then ... when then ... else... end

    -- case when then ... when then ...  when then ... else... end 
    
    select id,
    name,
    case depart_id when 1 then '第一部门' end v1,
    case depart_id when 2 then '第1部门' else '其他' end v2,
    case depart_id when 1 then '第一部门' when 2 then '第2部门' else '其他' end v3,
    case when age<18 then '少年' end v4,
    case when age<18 then '少年' else '油腻男' end v5,
    case when age<18 then '少年' when age<30 then '青年' else '油腻男' end v6
    from info;
    

3.7 排序(order by)

  • desc【降序】
    select * from info order by age desc;
    
  • asc【升序】
    select * from info order by age asc;
    

3.8 左右连表【多表查询】

  • 主表

    主表 left outer join 从表 on 主表.x=从表.id
    
    -- 左表连接,左边是主表
    -- 右表连接,右边是主表
    select * from info left outer join depart on info.depart_id=depart.id;
    select info.id,info.name,info.email,depart.title from info left outer join depart on info.depart_id=depart.id;
    
  • 从表

    从表 right outer join 主表 on 主表.x = 从表.id
    select info.id,info.name,info.email,depart.title from info right outer join depart on info.depart_id=depart.id;
    

3.9 联合【union】

  • 列数需相同【union】

     select id,title from depart 
     union 
     select id,name from info;
    
  • 【union】自动去重

    -- 注意:列的数据类型需要一致
     select id,title from depart 
     union 
     select id,name from info;
    
  • 获取所有【union all不去重】

    select id from depart
    union all 
    select id from info;
    

3.10 数据增删改

  • 修改数据
    UPDATE covid19_policy SET id=1 WHERE id=0;
    
  • 删除数据
     DELETE FROM covid19_policy WHERE ID = 2;
    
  • 添加数据
     INSERT INTO flow (id, date, "from","to",flow_people) VALUES (0, '2020-01-01', 1,2,1);
     -- 多行添加
     INSERT INTO flow (id, date, "from","to",flow_people) VALUES (500000002, '2020-01-01', 1,2,1),(500000001, '2020-01-01', 1,2,1);
    

4.表关系

4.1 一对多【设置一个外键】

  • 需要两张表来存储信息,且两张表存在一对多多对一关系
    • constraint fk_info1_depart1 foreign key (depart_id) references depart1(id)
    create table depart1(
        id int not null primary key,
        title varchar(16) not null
    );
    
    create table info1(
    	id int not null primary key,
    	name varchar(16) not null,
    	email varchar(32) not null,
    	age int,
    	depart_id int not null,
    	constraint fk_info1_depart1 foreign key (depart_id) references depart1(id)
    ) ;
    -- 如果表结构创建好了,额外添加外键
    alter table info1 add CONSTRAINT fk_info1_depart1 foreign key (depart_id) references depart1(id);
    -- 删除外键
    alter table info1 drop CONSTRAINT fk_info1_depart1;
    

4.2 多对多【设置多个外键】

  • 需要三张表来存储信息,两张单表+关系表,创造出两张单表之间多对多关系
    create table boy(
    id int not null primary key,
    name varchar(16) not null
    );
    
    create table girl(
    	id int not null primary key,
    	name varchar(16) not null
    );
    
    create table boy_girl(
    	id int not null primary key,
    	boy_id int not null,
    	girl_id int not null,
    	constraint fk_boy foreign key (boy_id) references boy(id),
    	constraint fk_girl foreign key (girl_id) references girl(id)
    );
    -- 创建表之后添加外键
    alter table boy_girl add constraint fk_boy foreign key (boy_id) references boy(id);
    alter table boy_girl add constraint fk_girl foreign key (girl_id) references girl(id);
    constraint fk_info1_depart1 foreign key (depart_id) references depart1(id)
    -- 删除外键
    alter table boy_girl drop CONSTRAINT fk_boy;
    alter table boy_girl drop CONSTRAINT fk_girl;
    

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