select e1.*,e2.ename 上级姓名 from emp e1 join emp e2 on e1.mgr=e2.empno 不等连接:连接条件是不等条件,(大于、小于、不等于) select e.*,s.grade,s.losal,s.hisal from emp e join salgrade s on e.sal between s.losal and s.hisal; 全连接:它会查出两个表中的所有数据 select 列名,列...
SELECTSno,SnameFROMStudent;/*若干列*/SELECT*FROMStudent;/*全部列*/SELECTDISTINCTSnoFROMSC;/*选择不重复的行*/SELECTSname,SageFROMStudentWHERESageBETWEEN20AND24;/*在某范围中,也可使用> < = 等比较运算*/SELECTSname,SageFROMStudentWHERESdeptIN('CS','GIS');/*判断在不在集合里,可以用 IN or NOT ...
insert into t_distinct(a,b) values(5,6); insert into t_distinct(a,b) values(6,7); 1.返回所有记录: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 # select a,b,c from t_distinct; a | b | c ---+---+--- 1 | 2 | 3 2...
消除重复记录的DISTINCT关键字的基本语法如下- SELECT DISTINCT column1, column2,...columnN FROM table_name WHERE [condition] 1. 2. 3. Distinct - 示例 考虑表 COMPANY 具有以下记录: # select * from COMPANY; id | name | age | address | salary ---+---+---+---+--- 1 | Paul | 32 ...
insert into emp values (4, 'jack'); insert into emp values (5, 'rose'); 三、初始化数据查看 select ctid, * from emp; image.png 四、重复数据查询 select distinct id, count(*) from emp group by id having count(*) > 1; 从结果来看id为1的有3条,id 为 2的2条。
SELECTdistinctname,age,count(*) 数据条数FROMuserGROUPBYname,age 张三202张三221李四201李四221 AI代码助手复制代码 二、查出重复数据后,我们需要删除重复数据 删除重复数据一般几种方式,一般采用 临时表 或者根据 某个字段,例如id等,通过max或者min函数去重。
PostgreSQL DISTINCT 关键字 在PostgreSQL 中,DISTINCT 关键字与 SELECT 语句一起使用,用于去除重复记录,只获取唯一的记录。 我们平时在操作数据时,有可能出现一种情况,在一个表中有多个重复的记录,当提取这样的记录时,DISTINCT 关键字就显得特别有意义,它只获取唯一一次记录,而不是获取重复记录。
INSERTINTOtest_id(uid)SELECTdistinct"CID"FROMtest_data; python pip installpsycopg2失败Error: pg_config executable not found. 需要安装 1. Error: pg_config executable not found. yum install postgresql-devel 2. error:command'gcc'failed withexitstatus1yum installlibpq-dev...
SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ] * | expression [ AS output_name ] [, ...] INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table [ FROM from_item [, ...] ] [ WHERE condition ] [ GROUP BY expression [, ...] ] [ HAVING condition [, ...] ] [ ...
CREATE TABLE new_table (LIKE my_table INCLUDING DEFAULTS INCLUDING CONSTRAINTS INCLUDING INDEXES); INSERT INTO new_table SELECT DISTINCT ON (data) * FROM my_table ORDER BY data, id; DROP TABLE my_table; ALTER TABLE new_table RENAME TO my_table; ...