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docs: update database related documentation and add new RDBMS guides
- 更新关系型数据库文档，增加主流数据库对比内容 - 添加 Oracle 数据库使用指南 - 添加 PostgreSQL 数据库使用指南 - 更新其他相关技术文档
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‎DBS/Oracle.md

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# Oracle
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[[toc]]
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## Flag
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* [Oracle with as + /*+ materialize*/ 优化](https://blog.csdn.net/qq_34745941/article/details/106897099)
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* [Oracle两种临时表的创建及使用方法](https://www.cnblogs.com/beloved-bq/p/12561512.html)
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* [https://docs.oracle.com/en/database/oracle/oracle-database/21/lnoci/preface.html](https://docs.oracle.com/en/database/oracle/oracle-database/21/lnoci/preface.html)
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> 空字符串''同等NULL，字符串与数字类型会自动转换
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> Oracle Call Interface（OCI）是Oracle提供的一组C语言API，用于开发Oracle数据库应用程序。
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> OCI提供了一种直接访问Oracle数据库的方式，使开发人员可以编写高效且可扩展的应用程序
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```sql
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-- 创建会话级临时表来存储原数据，并删除表数据
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CREATE GLOBAL TEMPORARY TABLE TEST_BAK AS (SELECT * FROM TEST);
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-- 查看临时表数据
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SELECT * FROM TEST_BAK;
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-- Oracle中类似于PostgreSQL的unnest
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-- https://docs.oracle.com/en/database/oracle/oracle-database/23/addci/extensibility-constants-types-and-mappings.html
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select * from table(sys.odcinumberlist(3,4,3))
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select * from table(sys.odcivarchar2list('3a','4b','3d'))
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-- 常量子查询
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字段 IN (SELECT 10000 FROM dual UNION ALL SELECT 20000 FROM dual)
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-- 清空数据 delete是dml操作；truncate是ddl操作，ddl隐式提交不能回滚，会回收表空间
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DELETE FROM TEST;
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-- 将目标字段数据清空
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--UPDATE TEST SET MEASURED = NULL;
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-- 修改表字段
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ALTER TABLE TEST MODIFY MEASURED NUMBER(18,6);
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-- 还原表结构
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INSERT INTO TEST SELECT * FROM TEST_BAK;
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-- 删除临时表
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DROP TABLE TEST_BAK;
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-- 替代LISTAGG拼接超4000字符长度
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SELECT
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REGEXP_REPLACE(RTRIM(XMLSERIALIZE(CONTENT XMLAGG(XMLELEMENT(E,colname,',').EXTRACT('//text()')) AS CLOB),', '),'(,)+',',') a,
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REGEXP_REPLACE(RTRIM(XMLAGG(XMLELEMENT(E,colname,',').EXTRACT('//text()')).getclobval(),','),'(,)+',',') b,
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REGEXP_REPLACE(RTRIM(REGEXP_REPLACE(XMLSERIALIZE(CONTENT XMLAGG(XMLELEMENT(e, colname || ',')) AS CLOB),'<E>|</E>',''),','),'(,)+',',') c
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FROM table_name
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GROUP BY grouping_column;
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```
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**系统表**
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- `USER_TABLES` 当前用户拥有的表：`TABLE_NAME`,`TABLESPACE_NAME`,`LAST_ANALYZED`
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- `DBA_TABLES` 包括系统表：多了`OWER`列
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- `ALL_TABLES` 所有用户的表：多了`OWER`列
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- `ALL_OBJECTS` 当前用户有访问权限的所有对象：`OWER`,`OBJECT_NAME`,`SUBOBJECT_NAME`,`OBJECT_ID`,`CREATED`,`LAST_DDL_TIME`,`TIMESTAMP`,`STATUS`
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- `USER_TAB_COLUMNS` 当前用户拥有的表字段
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- `ALL_TAB_COLUMNS`
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- `DBA_TAB_COLUMNS`
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- `USER_TAB_COMMENTS` 当前用户拥有的表注释 ：`TABLE_NAME`,`TABLE_TYPE`,`COMMENTS`
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- `DBA_TAB_COMMENTS` ：多了`OWER`列
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- `ALL_TAB_COMMENTS` ：多了`OWER`列
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- `USER_COL_COMMENTS` 当前用户拥有的表字段注释 ： `TABLE_NAME`,`COLUMN_NAME`,`COMMENTS`
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- `DBA_COL_COMMENTS` ：多了`OWER`列
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- `ALL_COL_COMMENTS` ：多了`OWER`列
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> `SELECT * FROM USER_TAB_COMMENTS WHERE COMMENTS LIKE '%摘要%'`
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**分组获取最新一条数据（查询各组最新的一条记录）**
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- over partition by 分析函数（开窗函数）
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```sql
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SELECT * FROM (
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SELECT ROW_NUMBER() OVER(PARTITION BY 分组字段名 ORDER BY 排序字段名 DESC) rn,t.* FROM test1 t
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) WHERE rn = 1;
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SELECT t.* FROM test1 t GROUP BY 分组字段名 ORDER BY 排序字段名 DESC FETCH FIRST 1 ROWS ONLY;
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SELECT * FROM (
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select eb_vipcode,eb_time,MAX(eb_time) over(partition by eb_vipcode) as "atime" from eb_daskexpdateinfo
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) x where eb_time = "atime";
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SELECT * FROM (
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select ID_,COMPANY_NAME,USAGE_RATE,CREATE_TIME
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,MAX(CREATE_TIME) over(partition by COMPANY_NAME) as "atime" from SPEC_RATE_ORIGIN
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) x where CREATE_TIME = "atime";
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```
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- group by
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```sql
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SELECT eb_vipcode,MAX(eb_time) AS "atime" FROM eb_daskexpdateinfo group by eb_vipcode
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```
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- inner join
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```sql
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SELECT A.* FROM SPEC_RATE_ORIGIN A INNER JOIN (
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SELECT COMPANY_NAME,MAX(CREATE_TIME) AS "atime" FROM SPEC_RATE_ORIGIN group by COMPANY_NAME
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) B ON A.COMPANY_NAME = B.COMPANY_NAME AND A.CREATE_TIME = B."atime";
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```
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**一次执行多条SQL**
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```sql
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INSERT ALL
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INTO a表(字段) VALUES(各个值1)
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INTO a表(字段) VALUES(其它值2)
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INTO a表(字段) VALUES(其它值3)
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SELECT 1 FROM DUAL;
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```
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- 使用`begin…end;`
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* [如何在Oracle中一次执行多条sql语句](https://www.cnblogs.com/teamleader/archive/2007/05/31/765943.html)
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```sql
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begin
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insert into table_name (列名,列名) values (express,express);
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insert into table_name (列名,列名) values (express,express);
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insert into table_name (列名,列名) values (express,express);
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insert into table_name (列名,列名) values (express,express);
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end;
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```
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**插入或更新 upsert**
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* [SQL语句 存在就更新不存在就插入](https://www.jianshu.com/p/602ba0b8395b)
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* [merge into 的用法](https://blog.csdn.net/weixin_40374341/article/details/109239544)
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```sql
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MERGE INTO table_name alias1
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USING (table|view|sub_query) alias2
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ON (join condition)
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WHEN MATCHED THEN
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UPDATE table_name SET col1 = col_val1
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WHEN NOT MATCHED THEN
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INSERT (column_list) VALUES (column_values);
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```
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**死锁**
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```sql
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-- 查询死锁会话
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SELECT l.session_id sid, s.serial#, l.locked_mode, l.oracle_username, l.os_user_name
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, s.machine, s.terminal, o.object_name, s.logon_time, p.SPID
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FROM v$locked_object l, all_objects o, v$session s,v$process p
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WHERE l.object_id = o.object_id AND l.session_id = s.sid AND s.paddr = p.addr
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ORDER BY sid, s.serial#;
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-- 结束
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alter system kill session 'sid,serial#';
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```
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```bash
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orakill SID spid
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```
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**查看所有表结构**
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```sql
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SELECT t1.Table_Name || chr(13) || t3.comments AS "表名称及说明",
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--t3.comments AS "表说明",
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t1.COLUMN_ID AS "序号",
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t1.Column_Name AS "字段名称",
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t1.DATA_TYPE || '(' || t1.DATA_LENGTH || ')' AS "数据类型",
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t1.NullAble AS "是否为空",
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t2.Comments AS "字段说明",
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t1.Data_Default AS "默认值"
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--t4.created AS "建表时间"
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FROM cols t1
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LEFT JOIN user_col_comments t2 ON t1.Table_name = t2.Table_name AND t1.Column_Name = t2.Column_Name
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LEFT JOIN user_tab_comments t3 ON t1.Table_name = t3.Table_name
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LEFT JOIN user_objects t4 ON t1.table_name = t4.OBJECT_NAME
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WHERE NOT EXISTS (
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SELECT t4.Object_Name
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FROM User_objects t4
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WHERE t4.Object_Type = 'TABLE' AND t4.Temporary = 'Y' AND t4.Object_Name = t1.Table_Name
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)
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ORDER BY t1.Table_Name, t1.Column_ID;
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-- 查询表字段信息
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WITH ct AS (
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SELECT u3.table_name,u3.column_name,u4.constraint_type FROM user_cons_columns u3
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JOIN user_constraints u4 ON u4.constraint_name=u3.constraint_name AND u4.constraint_type='P'
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)
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SELECT DISTINCT u1.column_id
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, u1.column_name
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, u1.data_type AS column_type
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, (CASE WHEN u1.data_type='NVARCHAR2' THEN u1.data_length/2 ELSE u1.data_length END) AS data_length
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, (CASE WHEN DECODE(u1.nullable, 'Y', 'N', 'N', 'Y', 'N')='Y' THEN 0 ELSE 1 END) AS nullable
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, u1.data_precision AS data_precision
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, u1.data_scale AS data_scale
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, u2.comments
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, DECODE(ct.constraint_type,'P','PRI') AS column_key
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FROM user_tab_columns u1
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LEFT JOIN user_col_comments u2 ON u1.table_name=u2.table_name AND u1.column_name=u2.column_name
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LEFT JOIN ct ON ct.table_name=u1.table_name AND ct.column_name=u1.column_name
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WHERE u1.table_name= '表名'
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ORDER BY u1.column_id
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```
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**日期时间**
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* [Oracle日期格式转换 to_date,to_char,to_timetamp 相互转换](https://blog.csdn.net/HaHa_Sir/article/details/125572325)
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```sql
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SELECT SYSDATE, SYSTIMESTAMP FROM dual;
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SELECT TO_CHAR(TO_TIMESTAMP('2023-05-08 10:10:10', 'yyyy-mm-dd hh24:mi:ss'), 'ww') FROM dual;
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-- 得到当天凌晨0点0分0秒的日期
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SELECT TRUNC(SYSDATE) FROM DUAL;
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-- 获取今天最后的时间（即午夜之前的那一刻）
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SELECT TRUNC(SYSDATE) + 0.99999 AS last_time FROM DUAL;
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SELECT TRUNC(SYSDATE) + 1 - 1/86400 AS last_time FROM dual;
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SELECT TRUNC(SYSDATE) + 1 - INTERVAL '1' SECOND AS last_time FROM DUAL;
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SELECT TRUNC(SYSDATE) + INTERVAL '1' DAY - INTERVAL '1' SECOND AS last_time FROM DUAL;
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SELECT TRUNC(SYSDATE) + INTERVAL '23' HOUR + INTERVAL '59' MINUTE + INTERVAL '59' SECOND AS last_time FROM DUAL;
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-- 获取本周开始日期（星期一）
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SELECT TRUNC(SYSDATE, 'IW') FROM DUAL;
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-- 获取本周结束日期（星期日）
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SELECT TRUNC(SYSDATE, 'IW') + 7 - 1 FROM DUAL;
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-- 获取当月开始时间和结束时间
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SELECT TRUNC(SYSDATE, 'MM') FROM DUAL
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SELECT TRUNC(LAST_DAY(SYSDATE))+ 0.99999 FROM DUAL
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-- 获取今年开始时间和结束时间
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SELECT TO_CHAR(TRUNC(SYSDATE, 'YYYY'), 'YYYY-MM-DD HH24:MI:SS') AS start_date,
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TO_CHAR(LAST_DAY(TRUNC(SYSDATE, 'YYYY') + 0.99999), 'YYYY-MM-DD HH24:MI:SS') AS end_date
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FROM dual;
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SELECT TO_DATE(EXTRACT(YEAR FROM SYSDATE) || '-01-01', 'YYYY-MM-DD HH24:MI:SS') AS start_date,
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TO_DATE(EXTRACT(YEAR FROM SYSDATE) || '-12-31 23:59:59', 'YYYY-MM-DD HH24:MI:SS') AS end_date
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FROM dual;
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SELECT TRUNC(SYSDATE, 'YYYY') AS start_date,
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TRUNC(SYSDATE + INTERVAL '1' YEAR, 'YYYY') - INTERVAL '1' SECOND AS end_date
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FROM dual
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-- FM格式模型来实现不要前导零
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SELECT TO_CHAR(SYSDATE, 'FMMM') AS one_digit_month
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FROM dual;
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-- 获取倒推时间列表
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SELECT TRUNC(sysdate - NumToDSInterval(level-1, 'hour'), 'MI') AS ds -- 'day','hour','minute','second'
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, TRUNC(sysdate - NumToYMInterval(level-1, 'month'), 'MI') AS ym -- 'year','month'
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FROM dual CONNECT BY level <= 12;
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SELECT TO_CHAR(Add_Months(TRUNC(sysdate,'YYYY'), Level-1), 'FMMonth') AS month_name FROM Dual CONNECT BY Level <= 12;
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SELECT TRUNC(SYSDATE - LEVEL/24, 'HH24') AS HOURMIN FROM DUAL CONNECT BY LEVEL <= 12 ORDER BY 1;
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-- 将数据按半小时进行分组
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SELECT TO_CHAR(record_date, 'YYYY-MM-DD HH24') || CASE WHEN TO_CHAR(record_date, 'MI') < '30' THEN ':00' ELSE ':30' END AS half_hour,
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SUM(col_8) AS total_money
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FROM table_name
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GROUP BY TO_CHAR(record_date, 'YYYY-MM-DD HH24') || CASE WHEN TO_CHAR(record_date, 'MI') < '30' THEN ':00' ELSE ':30' END
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SELECT TRUNC(record_date, 'HH24') + CASE WHEN TO_CHAR(record_date, 'MI') < '30' THEN INTERVAL '0' MINUTE ELSE INTERVAL '30' MINUTE END AS half_hour,
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SUM(col_8) AS total_money
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FROM table_name
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GROUP BY TRUNC(record_date, 'HH24') + CASE WHEN TO_CHAR(record_date, 'MI') < '30' THEN INTERVAL '0' MINUTE ELSE INTERVAL '30' MINUTE END
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```
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**随机取数**
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```sql
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SELECT *
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FROM test a
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--WHERE rownum = FLOOR(DBMS_RANDOM.VALUE(1, 10))
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WHERE MOD(rownum, floor(DBMS_RANDOM.VALUE(1, 10))) = 0
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FETCH FIRST ROW ONLY
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-- 重建排序
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SELECT * FROM (
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SELECT a.*, rownum as rn
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FROM test a
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)
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WHERE MOD(rn, floor(DBMS_RANDOM.VALUE(1, 1))) = 0
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ORDER BY dbms_random.value
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FETCH FIRST ROW ONLY;
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-- Oracle类PostgreSQL的generate_series函数
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SELECT ROWNUM AS num FROM dual CONNECT BY ROWNUM <= 3;
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SELECT LEVEL AS num FROM DUAL CONNECT BY LEVEL <= 3;
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-- 使用序列
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CREATE SEQUENCE seq_num START WITH 1 INCREMENT BY 1 NOMAXVALUE;
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SELECT NEXT VALUE FOR seq_num AS num FROM DUAL WHERE NEXT VALUE FOR seq_num <= 3;
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```
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