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APP INVENTOR硬件交互学习教程03——巧借arduino nano 配置HC-05 - 创客硬...
1.HC-05模块有两种模式
配置模式：进入方式，上电前按住模块按键，通电LED慢闪即进入配置模式，默认波特率38400，数据为8，停止位1
通信模式：不按下按键，上电就是这个模式，默认串口波特率9600，数据位8，停止位1
2.ardu...
【解决】模拟器启动失败：ERROR: x86_64 emulation currently requires har...
ERROR: resizing partition elfsck failed with exit code 8
handle puAcceleration: feature check for hvf emulator: ERROR: x86_64 emulation currently requires
hardware acceleration!
CPU acceleration status: Hill is not installed on this machine
解决方法：
安装硬件加速器，路径：
....
How to request a random row in SQL?
...
See this post: SQL to Select a random row from a database table. It goes through methods for doing this in MySQL, PostgreSQL, Microsoft SQL Server, IBM DB2 and Oracle (the following is copied from that link):
Select a random row with MySQL:
SELE...
Select row with most recent date per user
...
Query:
SQLFIDDLEExample
SELECT t1.*
FROM lms_attendance t1
WHERE t1.time = (SELECT MAX(t2.time)
FROM lms_attendance t2
WHERE t2.user = t1.user)
Result:
| ID | USER | TIME | IO |
---------------------------...
Difference between left join and right join in SQL Server [duplicate]
...
Select * from Table1 left join Table2 ...
and
Select * from Table2 right join Table1 ...
are indeed completely interchangeable. Try however Table2 left join Table1 (or its identical pair, Table1 right join Table2) to see...
Table name as variable
...mpare data between the same tables of different databases:
static query:
SELECT * FROM [DB_ONE].[dbo].[ACTY]
EXCEPT
SELECT * FROM [DB_TWO].[dbo].[ACTY]
since I want easily change tha name of table and schema I have created this dynamic query:
declare @schema varchar(50)
declare @table varchar(5...
Oracle SQL: Update a table with data from another table
...his is called a correlated update
UPDATE table1 t1
SET (name, desc) = (SELECT t2.name, t2.desc
FROM table2 t2
WHERE t1.id = t2.id)
WHERE EXISTS (
SELECT 1
FROM table2 t2
WHERE t1.id = t2.id )
Assuming the join results in a key-pr...
How to disable text selection highlighting
...S standard way to disable the highlighting effect if the user accidentally selects the text?
48 Answers
...
Get top n records for each group of grouped results
...ould need to specify the group number and add queries for each group:
(
select *
from mytable
where `group` = 1
order by age desc
LIMIT 2
)
UNION ALL
(
select *
from mytable
where `group` = 2
order by age desc
LIMIT 2
)
There are a variety of ways to do this, see this articl...
How to add extra info to copied web text
...cument.location.href}`;
event.clipboardData.setData('text', document.getSelection() + pagelink);
event.preventDefault();
});
Lorem ipsum dolor sit amet, consectetur adipiscing elit.<br/>
<textarea name="textarea" rows="7" cols="50" placeholder="paste your copied text here"></...