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App Inventor 2 MQTT拓展入门（保姆级教程） · App Inventor 2 中文网
...) 等。有一定基础的可以考虑用英文平台。
其实，使用哪个平台都可以，甚至自己搭建MQTT服务器，用自己的平台。不过初学者还是建议用国内中文平台进行测试，熟悉之后可以研究一下其他的或者自己搭建。
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Counting DISTINCT over multiple columns
... Excellent suggestion! The more I read, the more I am realizing that SQL is less about knowing syntax and functions and more about applying pure logic.. I wish I had 2 upvotes!
– tumchaaditya
Oct 4 '13 at 22:48
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Ruby: Can I write multi-line string with no concatenation?
...ere's a version using funny HEREDOC syntax (via this link):
p <<END_SQL.gsub(/\s+/, " ").strip
SELECT * FROM users
ORDER BY users.id DESC
END_SQL
# >> "SELECT * FROM users ORDER BY users.id DESC"
The latter would mostly be for situations that required more flexibility in ...
SQL Server Profiler - How to filter trace to only display events from one database?
How do I limit a SQL Server Profiler trace to a specific database? I can't see how to filter the trace to not see events for all databases on the instance I connect to.
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Select top 10 records for each category
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If you are using SQL 2005 you can do something like this...
SELECT rs.Field1,rs.Field2
FROM (
SELECT Field1,Field2, Rank()
over (Partition BY Section
ORDER BY RankCriteria DESC ) AS Rank
FROM t...
Is it possible to for SQL Output clause to return a column not being inserted?
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Maybe someone who uses MS SQL Server 2005 or lower will find this answer useful.
MERGE will work only for SQL Server 2008 or higher.
For rest I found another workaround which will give you ability to create kind of mapping tables.
Here's how Resol...
Is there a ternary conditional operator in T-SQL?
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In SQL Server 2012, you could use the IIF function:
SELECT *
FROM table
WHERE isExternal = IIF(@type = 2, 1, 0)
Also note: in T-SQL, the assignment (and comparison) operator is just = (and not == - that's C#)
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Oracle SQL Query for listing all Schemas in a DB
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Using sqlplus
sqlplus / as sysdba
run:
SELECT *
FROM dba_users
Should you only want the usernames do the following:
SELECT username
FROM dba_users
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Inserting multiple rows in mysql
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Use mysql multiqueries
– Francisco Yepes Barrera
Nov 9 '15 at 16:10
1
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Oracle SQL, concatenate multiple columns + add text
...ch for this answer. I like the '||' as it makes it easier to maintain the SQL query.
– Jason TEPOORTEN
Oct 25 '12 at 0:56
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