oracle 学习笔记

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select * from goodscenter.sysmenu t

--坚检测 parentid不为空

select * from goodscenter.sysmenu t WHERE t.parentid IS NULL

-- 检测parentid 不等于""或者是null <>1

select * from goodscenter.sysmenu t WHERE t.parentid <>1

select * from goodscenter.sysmenu t WHERE t.parentid <>1 AND parentid='11000'

--采取伪列 rownum
select * from goodscenter.sysmenu t WHERE ROWNUM <20 ORDER BY id

select t.*,ROWID from goodscenter.sysmenu t WHERE ROWID

--连接操作符号||'String'||

select t.NAME || '_' ||t.parentid AS c from goodscenter.sysmenu t

select * from goodscenter.sysmenu t WHERE t.parentid !>t.id

--count(*)关键字意思是说返回表中所有条数的总和、意思是有多少条数据

select Count(*) AS count from goodscenter.sysmenu t

--1 case when 的用法          1                                                              --

                 select t.id, CASE t.parentid

WHEN 15000 THEN '_________'

ELSE '不知道' END AS cb

from goodscenter.sysmenu t ORDER BY t.id

--2 case when 的用法 2

                 select t.id, CASE

                               WHEN t.parentid>12000 AND t.parentid<13001 THEN '_________1'

                               WHEN t.parentid>13000 AND t.parentid<14001 THEN '_________2'

ELSE '不知道' END

AS cb

from goodscenter.sysmenu t ORDER BY t.id