Rollback | Commit
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in 2 separate command prompts (ie 2 separate sessions), if one of them deletes a table, when the other also tries to modify the table somehow, it (the second one) is put on hold.
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The first one needs to either rollback, un-deleting the data, or commit and actually delete the data table.
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the process of editing data all the way up to the rollback / commit is called a "transaction"
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ingeneral, when you do an insert/update/delete query, it's a rule to commit or rollback ASAP.
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It's meaningful to note that Oracle and DB2 allows entry-specific locks, while others like SQL server only have table locks.
PHP - arrays
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you can put text as array keys, not just numbers. usually in other coding langauges, you can only use numbers as keys for arrays.
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some useful functions:
- count(); counts the number of elements in an array
- print_r(); --> to print an array
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foreach ---> easy to use, but only good for certain cases. For instance, you have to loop through every single element in the array with a foreach loop, while for-loops allow for sectional loops.
foreach usage: foreach ($array as $value) {} or foreach ($array as $key => $value) {}
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if you go to php.net, you'll be able to find a function that sorts an array
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in PHP, each element in an array is basically a variable.
