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MySQL: selecting rows where a column is null
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SQL NULL's special, and you have to do WHERE field IS NULL, as NULL cannot be equal to anything,
including itself (ie: NULL = NULL is always false).
See Rule 3 https://en.wikipedia.org/wiki/Codd%27s_12_rules
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投屏（ScreenCast）使用指导 · App Inventor 2 中文网
...：文本, 媒体地址：文本。设置投屏媒体的元数据信息，包括标题、艺术家和媒体地址。
开始投屏播放（StartCastPlayback）
无参数。开始在投屏设备上播放媒体内容。
停止投屏播放（StopCastPlayback）
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How to escape apostrophe (') in MySql?
The MySQL documentation says that it should be \' . However, both scite and mysql shows that '' works. I saw that and it works. What should I do?
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Foreign key constraint may cause cycles or multiple cascade paths?
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SQL Server does simple counting of cascade paths and, rather than trying to work out whether any cycles actually exist, it assumes the worst and refuses to create the referential actions (CASCADE): you can and should still cr...
Read data from SqlDataReader
I have a SQL Server 2008 database and I am working on it in the backend. I am working on asp.net/C#
13 Answers
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Copy a table from one database to another in Postgres
...it directly to the target database:
pg_dump -t table_to_copy source_db | psql target_db
Note: If the other database already has the table set up, you should use the -a flag to import data only, else you may see weird errors like "Out of memory":
pg_dump -a -t my_table my_db | psql target_db
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Which are more performant, CTE or temporary tables?
...y to other constructs that can also be used as inline table expressions in SQL Server. Derived tables, Views, and inline table valued functions. Note that whilst BOL says that a CTE "can be thought of as temporary result set" this is a purely logical description. More often than not it is not materl...
MySQL ON vs USING?
In a MySQL JOIN , what is the difference between ON and USING() ? As far as I can tell, USING() is just more convenient syntax, whereas ON allows a little more flexibility when the column names are not identical. However, that difference is so minor, you'd think they'd just do away with USI...
What is the difference between Scope_Identity(), Identity(), @@Identity, and Ident_Current()?
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This is a role model answer. In particular, working with SQL and SQL Server can be weird, and this explains things in a very clear, layman's manner, while still being fairly informative. It doesn't sound like something being communicated between two database specialists, which a L...
SQL Server indexes - ascending or descending, what difference does it make?
When you create an index on a column or number of columns in MS SQL Server (I'm using version 2005), you can specify that the index on each column be either ascending or descending. I'm having a hard time understanding why this choice is even here. Using binary sort techniques, wouldn't a lookup be ...