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Computed / calculated / virtual / derived columns in PostgreSQL
...s defined in the SQL standard and implemented by some RDBMS including DB2, MySQL and Oracle. Nor the similar "computed columns" of SQL Server.
STORED generated columns are introduced with Postgres 12. Trivial example:
CREATE TABLE tbl (
int1 int
, int2 int
, product bigint GENERATED ALWAYS...
Mechanisms for tracking DB schema changes [closed]
...se.
Make a backup of the current database (because stuff will go wrong) [mysqldump].
Create bookkeeping table (called _meta) if it doesn't exist.
Read current VERSION from _meta table. Assume 0 if not found.
For all .sql files numbered higher than VERSION, execute them in order
If one of t...
Why should I capitalize my SQL keywords? [duplicate]
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So does MySQL, and for good and for bad (mostly bad:-), many developers first exposure to SQL is through MySQL.
– Paul Tomblin
Mar 4 '09 at 13:41
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Database Structure for Tree Data Structure
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Have a look at Managing Hierarchical Data in MySQL. It discusses two approaches for storing and managing hierarchical (tree-like) data in a relational database.
The first approach is the adjacency list model, which is what you essentially describe: having a foreign key...
How can I create tests in Android Studio?
...m the base of the test, but if I run in Android Studio, the tests run from root_/app, however if I run from Gradle command line (or CI) then it is _root. (Ideally I'd like to access specific assets folders when run either way).
– mm2001
May 6 '17 at 18:21
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How to set background color of an Activity to white programmatically?
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Get a handle to the root layout used, then set the background color on that. The root layout is whatever you called setContentView with.
setContentView(R.layout.main);
// Now get a handle to any View contained
// within the main layout y...
How to show first commit by 'git log'?
... answer was posted.)
Explanation
Technically, there may be more than one root commit. This happens when multiple previously independent histories are merged together. It is common when a project is integrated via a subtree merge.
The git.git repository has six root commits in its history graph (o...
How to install python modules without root access?
...asy_install to install python packages in your home directory even without root access. There's a standard way to do this using site.USER_BASE which defaults to something like $HOME/.local or $HOME/Library/Python/2.7/bin and is included by default on the PYTHONPATH
To do this, create a .pydistutils...
How do I insert datetime value into a SQLite database?
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Use CURRENT_TIMESTAMP when you need it, instead OF NOW() (which is MySQL)
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How do I create a crontab through a script
...moving existing crontab entries and also I needed to use a different user (root) so I used the following to maintain the existing entries: echo -e "$(sudo crontab -u root -l)\n* * * * * echo hello > /home/danny/temp.log 2>&1" | sudo crontab -u root - Hopefully this helps someone
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