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MySQL COUNT DISTINCT
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BIO与NIO、AIO的区别(这个容易理解) - 操作系统(内核) - 清泛网 - 专注C/C++及内核技术
...给OS处理，需要将数据缓冲区地址和大小传给OS(银行卡和密码)，OS需要支持异步IO操作API）；
阻塞 ： ATM排队取款，你只能等待（使用阻塞IO时，Java调用会一直阻塞到读写完成才返回）；
非阻塞 ： 柜台取款，取个号，然后坐在...
Insert, on duplicate update in PostgreSQL?
...rom an answer on Stack Overflow how to perform multiple updates at once in MySQL using the following syntax:
16 Answers
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SQL how to make null values come last when sorting ascending
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@Martin Note this question is not tagged mysql. I provided a generalized solution - there are many different ways of doing the same thing across different dbs.
– RedFilter
Oct 16 '15 at 14:15
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How to properly create composite primary keys - MYSQL
...ep these as two distinct columns. You could use a two-column primay key in mysql ...PRIMARY KEY(id_a, id_b)... but I prefer using a two-column unique index, and having an auto-increment primary key field.
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Return rows in random order [duplicate]
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For MySQL use ORDER BY uuid(). (...for those arriving on this page via a generic search, like me!)
– Stan James
Jan 7 '12 at 4:15
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Is there a Boolean data type in Microsoft SQL Server like there is in MySQL? [duplicate]
Is there a Boolean data type in Microsoft SQL Server like there is in MySQL?
9 Answers
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Storing JSON in database vs. having a new column for each key
...figured it was worth an update.
When this question was originally posted, MySQL had no support for JSON data types and the support in PostgreSQL was in its infancy. Since 5.7, MySQL now supports a JSON data type (in a binary storage format), and PostgreSQL JSONB has matured significantly. Both prod...
How to use GROUP_CONCAT in a CONCAT in MySQL
If I have a table with the following data in MySQL:
7 Answers
7
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MySQL Removing Some Foreign keys
I have a table whose primary key is used in several other tables and has several foreign keys to other tables.
11 Answers
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