Recent comments in /f/explainlikeimfive

DeHackEd t1_jegltx8 wrote

Reply to ELI5: Can someone please explain to me the difference between a primary key, foreign key, clustered index, natural key, and surrogate key? by justin7465

"Keys" are selections of column in a table that are indexed in some way, intended to allow for much faster searching. Typically the index is stored in a different file from the raw table records. With that said...

A "primary key" is the key designed to uniquely identify rows in a table. So if a primary key is defined on columns (a,b,c) then a search with condition "WHERE a=1 AND b=2 AND c=3" will turn up exactly 0 or 1 rows. 2+ rows are impossible. As a result, rules that may allow multiple row matches, especially where NULL is involved, are forbidden. For example, if you run a shopping store, then products could be uniquely identified by their barcode numbers. Duplicate of that should never happen, and if they do then yeah you have a problem that needs solving anyway.

A "foreign key" is a cross-reference between tables. Table X may have a column named A and it's a foreign key reference to table Y which also has a column named A (typically the same name to help reinforce they are the same piece of information for that cross-reference). The database may refuse to allow you to delete information in one table because the other references it, or the act of deleting from one table may cause deletion of data in the other table to keep the foreign key requirements met, depending on settings. It also helps software visualize the relationship between the tables. For example, if you have a table of customers, and a table of outstanding orders, you may not delete a customer if they have any outstanding orders placed, but deleting orders is fine.

"Clustered index" means the actual raw records on disk are sorted to this ordering. There can be advantages to that if you are fetching large amounts of data and you want it delivered pre-sorted... if you ask for it in the same sort order that the clustered index is provided in, then the DB just does sequential disk reads and gets data back pre-sorted, solving that problem without needing to actually perform a sort in memory or anything.

Now let's go back to the primary key: a unique way to identify rows. How do you actually do that? There's 2 common strategies: a unique number typically starting at 1 and counting up indefinitely, or finding some set of columns that are actually enough to uniquely identify a row. The former is what we call a "surrogate" key - something we introduced to assist. The latter is what we call a natural key - something already provided. For our list of products, barcodes make a pretty good natural key. For our customers, names aren't unique, even addresses aren't uniqu and we don't have anything we can give them (damned customers keep refusing our loyalty cards) so we just give them a customer number and each new customers gets the next number. That's a surrogate key. Customers might see the number on their invoices, but by itself the number doesn't mean thing.

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Xerxeskingofkings t1_jeglfm9 wrote

Reply to ELI5: How does salt seemingly hydrate you and dehydrate you at the same time. They always say you need electrolytes (salt?) for hydration, then why can’t we drink sea water? by TriCombington

short answer: Osmosis.

your kidneys rely on osmosis ( an effect that "pulls" water form low concentration mixes to higher ones to equalise the mix strengths) to move waste materials out of the blood and into urine.

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thus, to shift a lot of salt out of the body, you need to loose a lot of water, which dehydrates you.

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parks_canada t1_jegl34r wrote

Reply to comment by coniferous-1 in ELI5: If benzodiazepines are CNS depressants, why is it so hard to die from a overdose of them alone? by psychrolute

RC stands for research chemical, and sometimes they're called designer drugs. Really it refers to any chemical that isn't well studied and understood, but typically when people talk about RCs they're referring to drugs that aren't federally scheduled, and which fall into a legal grey area in many cases (allowing them to be sold on the open market). A lot of these are analogues of scheduled drugs, for example:

  • Clonazolam ("CLAM"), an analogue of clonazepam (Klonopin)
  • 1P-LSD, an analogue of LSD
  • MDMC, an analogue of MDMA
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Steamvolt t1_jegktxp wrote

Reply to comment by psychrolute in ELI5: If benzodiazepines are CNS depressants, why is it so hard to die from a overdose of them alone? by psychrolute

I doubt snorting would make it stronger. Benzos have a high bioavailability when swallowed. They dont dissolve in water so unlikely to be absorbed through blood mucus membranes. However it would have ended up in your stomach eventually. I lost 2 days my phone, geekvape 200 and crashed my 30 mph ebike. Without even knowing. Woke up 3 days later with black eye cut head etc. Dont even know how I got up 4 flights of stairs. I dont remember a thing about it. I hadn't been out is what I thought Eventually enough people who saw me said how fucked up and confused I Was. Expensive day and lucky I didn't kill myself accidentally again. My TV was also broken and my flat looked like it had been ransacked This isn't the first time but the last from know on its only Legit Diazepam like Kern prodes

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DamnThatsLaser t1_jegks6k wrote

Reply to comment by coniferous-1 in ELI5: If benzodiazepines are CNS depressants, why is it so hard to die from a overdose of them alone? by psychrolute

"RC" in this context means Research Chemical, these are substances that are usually novel and as such not yet well researched and regulated. They are called research chemicals because you're free to do your own "research on them" since there's no law stopping you from doing it. They often can be ordered from specialized vendors or from another country where manufacturing is done, like India or China.

These can either be actual novel substances in a given class or designer prodrugs that were invented to circumvent existing laws, for the latter 1p-LSD is an example, it's technically not LSD so it was legal but it turns into LSD in your body so it's not only mimicking the effect in another way like NBOMe, but it becomes the real thing. Anyhow, the downside with the other RC drugs is that there's usually little to no reliable scientific information about toxicity and other long term effects.

Benzos which this thread is about is a class of depressant drugs. But I guess you knew that already. I don't think they're very popular over here in Germany though.

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Uruz2012gotdeleted t1_jegkp9j wrote

Reply to ELI5: If benzodiazepines are CNS depressants, why is it so hard to die from a overdose of them alone? by psychrolute

Benzos are effective at slowing the frequency and intensity of flases of activity in the brain. Klonopin is used as an anti sezure medication because of this effect. Seizures amount to a confused firing of many areas cascading from one anomalous, intense firing of one area. Flashing lights are a common trigger, for example.

None of that will stop you from breathing, just level out your heartrate and respiratory speed.

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LouSanous t1_jegkndd wrote

Reply to ELI5: why does the US need the dollar to be the only primary form of currency for oil? by aresyves

The US maintains the trade of oil for dollars at the point of a gun.

They do this because it allows the US to create a perpetual demand for dollars worldwide. That demand maintains the value of the currency.

This allows for unequal exchange, where the US can purchase goods from around the world for significantly less than they are worth, maintaining poverty and thus cheap labor around the world.

It also simultaneously allows the US to maintain trade deficits without losing the value of its currency. Thus Americans can consume multiple times what other people around the world consume without having to actually produce it. It also allows US people to have an advantage in any transaction abroad.

All currency is convertible to another currency. The arguments that somehow accounting for fluctuating currencies makes the system easier ignores that the US dollar fluctuates in value just as every other currency does. The real reason for this arrangement is that it is a major part of US economic hegemony.

When the US controls oil via its financial systems and enforces this rule militarily, the US becomes, in a sense, the de facto ruler of the world as oil is a necessary resource for every modern economy.

The reason we are starting to see this break down is because the Chinese have shifted the world's economic center of gravity eastward while alternative forms of energy are becoming more and more viable. Oil will have to be abandoned for climate change eventually, so it makes sense for other countries to start pushing back now, rather than waiting for later.

It should be clear that the USD being the forced currency for oil is a great arrangement for the US and a shitty one for everyone else.

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Any-Growth8158 t1_jegkh41 wrote

Reply to comment by breovus in ELI5 Leasing vs Purchasing by SquishyEmerald

100% agree. A financial planner advising to lease is not someone who I want controlling my money--unless you specifically tell them that you only want to drive a new car and get a new one every three years and ALWAYS have a car payment.

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not_today_trebeck t1_jegk3py wrote

Reply to ELI5: What actually happens when you call your representatives? by glitterismyantidrug_

An intern will answer the phone then may or may not actually record your name and comment then it's completely up in the air if the representative gets that memo. You will however be almost guaranteed to get a form letter, most likely written by AI at this point, about how much your comments mean to the person and how your views are important to consider. You will then be signed up for every newsletter, email, and town hall call that rep does forever.

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