oracle常用查询记录

下面记录了一些平时遇到的查询语句：

1.级联查询

select *
from (表名)
start with (根字段)(条件) --例如：root_field in (#{查询条件})
connect by prior (子节点字段) = (父节点字段)

向上递归时只需将连接条件改为：（父节点字段）=（子节点字段）

2.分页查询

select *
from (
select t.*, rownum as r from (表名) t where rownum <= #{a}
)
where r>#{b}

传参时：
int a = currPage*pageSize;
int b = (currPage-1)*pageSize;

3.导出表结构到Excel

查询表结构语句

SELECT t1.Table_Name AS "表名称",
t3.comments AS "表说明",
t1.Column_Name AS "字段名称",
t1.DATA_TYPE || '(' || t1.DATA_LENGTH || ')' AS "数据类型",
t1.NullAble AS "是否为空",
t2.Comments AS "字段说明",
t1.Data_Default AS "默认值",
t4.created AS "建表时间"
FROM cols t1
LEFT JOIN user_col_comments t2 ON t1.Table_name = t2.Table_name
AND t1.Column_Name = t2.Column_Name
LEFT JOIN user_tab_comments t3 ON t1.Table_name = t3.Table_name
LEFT JOIN user_objects t4 ON t1.table_name = t4.OBJECT_NAME
WHERE NOT EXISTS
(SELECT t4.Object_Name
FROM User_objects t4
WHERE t4.Object_Type = 'TABLE'
AND t4.Temporary = 'Y'
AND t4.Object_Name = t1.Table_Name)
order by t1.TABLE_NAME, t1.COLUMN_ID

使用pl/sql在查询结果上方点击“导出查询结果”，选择导出HTML文件，更改文件后缀名为.xls，即可保存表数据到Excel中。或者直接保存为csv格式。

4.查询指定年指定月的每一天

其中年份和月份’202002’是变量，

SELECT TRUNC(to_date('202002', 'yyyyMM'), 'MM') + ROWNUM - 1 as day
FROM DUAL
CONNECT BY ROWNUM <= TO_NUMBER(TO_CHAR(LAST_DAY(to_date('202002', 'yyyyMM')), 'dd'))

5.查询当前年份每一天

其中年份’2020’是变量，

SELECT TRUNC(to_date('2020', 'yyyy'), 'YYYY') + ROWNUM - 1 as day
FROM DUAL
CONNECT BY ROWNUM <= ADD_MONTHS(TRUNC(to_date('2020', 'yyyy'), 'YYYY'), 12) - TRUNC(to_date('2020', 'yyyy'), 'YYYY')

持续更新中…