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Can table columns with a Foreign Key be NULL?

...NGINE=INNODB; CREATE TABLE child (id INT NULL, parent_id INT NULL, FOREIGN KEY (parent_id) REFERENCES parent(id) ) ENGINE=INNODB; INSERT INTO child (id, parent_id) VALUES (1, NULL); -- Query OK, 1 row affected (0.01 sec) INSERT INTO child (id, parent_id)...
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What are the basic rules and idioms for operator overloading?

...ey. The canonical form of providing these is this: class X { value_type& operator[](index_type idx); const value_type& operator[](index_type idx) const; // ... }; Unless you do not want users of your class to be able to change data elements returned by operator[] (in which cas...
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Kotlin Ternary Conditional Operator

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Should JAVA_HOME point to JDK or JRE?

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Convert Linq Query Result to Dictionary

...000/svg\"\u003e\u003cpath d=\"M46.1709 9.17788C46.1709 8.26454 46.2665 7.94324 47.1084 7.58816C47.4091 7.46349 47.7169 7.36433 48.0099 7.26993C48.9099 6.97997 49.672 6.73443 49.672 5.93063C49.672 5.22043 48.9832 4.61182 48.1414 4.61182C47.4335 4.61182 46.7256 4.91628 46.0943 5.50789C45.7307 4.9328 4...
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Properties file in python (similar to Java Properties)

... James OravecJames Oravec 15.7k2323 gold badges7474 silver badges139139 bronze badges ...
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Rake just one migration

...n dropped from the database outside of Rails, rake db:migrate:up VERSION=my_version may do nothing, because the schema_migrations table still says it is has been run. In the same situation rake db:migrate:redo VERSION=my_version may fail because it cannot drop the table. In this case, comment out th...
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Grouped LIMIT in PostgreSQL: show the first N rows for each group?

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How to run a Runnable thread in Android at defined intervals?

... You may define boolean variable _stop, and set it 'true' when you want to stop. And change 'while(true)' into 'while(!_stop)', or if the first sample used, just change to 'if(!_stop) handler.postDelayed(this, 1000)'. – alex2k8 ...
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Sort a list from another list IDs

...000/svg\"\u003e\u003cpath d=\"M46.1709 9.17788C46.1709 8.26454 46.2665 7.94324 47.1084 7.58816C47.4091 7.46349 47.7169 7.36433 48.0099 7.26993C48.9099 6.97997 49.672 6.73443 49.672 5.93063C49.672 5.22043 48.9832 4.61182 48.1414 4.61182C47.4335 4.61182 46.7256 4.91628 46.0943 5.50789C45.7307 4.9328 4...