Horatio: I need a report on all the walls ever made ever. Tech Guy: I'm on it... According to this, this particular model of wall is of an excellent quality. It doesn't creak. Unless... there's a body behind it.
No matter what sort of clue the Crime Scene lab has found (blood, wire, rope, oil, perfume, etc), somebody has manufactured a database designed to search through them all. Not only that, our heroes at the crime lab have purchased a copy of this software, the interface devices to input the data in question and have acquired the expertise to use this software (which has so far never been used in another one of their cases) with 100% accuracy on the first attempt.
It should be noted that some of these "Omniscient Databases" actually exist, and are in use by various agencies, though they aren't quite as stunningly accurate or omniscient as the Police Procedural suggests. In real life, "Data Mining" is a time-consuming task that has to be practiced. Does each agency host a different server? Which ones pull from each other? Are all servers identical? Are there delays in updating the databases? These are all questions the searcher needs to be aware of, and there is no single database that stores 100% of the information.
A key aspect of this trope is that there must be a pre-existing compendium of all possible samples of whatever is being identified. In Real Life, forensics can indeed match samples of, say, paint or glass not only down to manufacturer but even to a specific batch, but this requires two samples: one sample from evidence, and another sample to compare against. This also means that in real forensics, the implications of this evidence are different; while crime dramas typically use the Omniscient Database to find a new lead from trace evidence, real forensics usually confirms identity after the police have already gotten a lead (i.e. the police already suspect the glass came from the suspect's house or workplace and can prove it by comparing them, as opposed to identifying where the suspect lives with no prior knowledge just from the glass sample).
Even in cases where there are well established databases, like criminal records, there are computer scientists who have dedicated entire careers just figuring out how to combine databases from various departments and institutions. When computers first started to be used for keeping criminal records, standardization was rarely considered, as they were for the use of that department alone, unless they were in a particularly forward-thinking county or large city where they shared records among local departments. It rapidly became apparent that this was a problem when departments began sharing records over the internet. One database may describe a criminal's eyes as "Light blue", another as "BL" and a third as "Lb". The same departments would describe another criminal's eyes as "Dark Brown", "BrD", and "B". This is after you manage to figure out which column denotes eye color, mind you. Even after the problem was discovered, change was slow because in some cases, such as New York and London, the same basic forms had been used for over 100 years, and had simply been transferred from index card to hard drive.
Forensics labs also have an out for many of these Omniscient Databases, since it's generally believable that they would have a database of common murder weapons or components of weapons.
Omniscient Databases almost always have a Viewer-Friendly Interface. If it's on paper or supernatural, it's a Great Big Book of Everything. See Akashic Records for a related but older trope. These are a special Applied Phlebotinum used primarily in Police Procedural dramas, sometimes ones with a supernatural element.
Inspector Runge from Monster keeps an absurdly expansive encyclopedia on practically everything in his head by constantly making a typing motion and saying that he's just calling up the memories as he needs them, or something along those lines.
Almost every depiction of Batman has this, whether it's his own vast knowledge (a la Sherlock Holmes), the Batcave computer, or a combination of both. In one Justice League of America issue, it is shown that Batman's database of fingerprints looks at the magical databases of the Batcave, the GCPD, AFIS, JLA Headquarters and Superman's fortress of solitude. This allows him to determine the identity of a 31st century superhero because Superman had been friends with him in the past... err... future...
Oracle has taken on the role of database for the hero community at large. She serves as information retriever and disseminator, as well as offering mission-specific hacking and guidance.
In an issue of Gotham Central, which focused on the members of the Major Crimes Unit of the Gotham City Police Department, ReneeMontoya was attempting to track down the history of a sniper rifle that had been used in several high-profile assassinations. She is seen accessing numerous government databases, including the FBI and ATF, but none of them can give her any useful information. When she mysteriously gains access to a system named "Oracle," which neither she nor her partner can identify, she is shocked (but happy) when it suddenly gives her the complete history of the gun, including the gun shop where it was sold.
The Flash: Impulse is the only Flash able to permanently remember what he reads at super-speed. Once, he read an entire San Francisco public library. It came in less handy than you'd think.
Subverted in Queen And Country - when trying to identify a man on a video being used to blackmail a well-known telecom industrialist, the technicians mention to Crocker that they ran his face through a visual database to match him to someone on file. Crocker asks if that actually worked, and one of the techs says it never does, mentioning that the database always wants to match the subject to the late Queen Mother.
Subverted in Mr. and Mrs. Smith: When the eponymous female character commands her subordinates to "search the database!", she gets rebutted with a snarky "For what? John Smith?"
Holmes kept such databases in his head, being able to identify, for example, varieties of tobacco after examination of the ash (he had "written a monograph" on the subject). He also had a substantial collection of home-made biographies, which were usually spoken aloud by Watson for the reader's benefit. So, despite its modern-tech dressing, this is a pretty old detective-story trope.
Lord Peter Wimsey series: Wimsey is a living magical database. He also had a home-made "Who's Who" of the underworld, and once managed to identify the maker of a hat which had had its label removed, purely from the style. (Parker remarks that if he hadn't got the hatter, they'd have tried him on the man's dress suit, similarly de-labelled.)
The Archive in is a being that holds the knowledge of everything ever written down, ever, in the history of mankind. Her information is updated in real-time, a fact which Harry puts to good use in Small Favor.
There's also Bob, Harry's knowledge spirit in a skull. Bob doesn't have the extensive knowledge of the Archive, but he is Dresden's go-to guy for magical knowledge, and he instinctively knows the current rules of magic.
The Secret Histories: The Karma Catechist is a living database of every spell, ritual and magical concept conceivable in his universe.
In "Under A Velvet Cloak", we find that Nox, the Mistress of Secrets, received a highly advanced database, which she always has with her. Since her Office receives all secrets, her database becomes this. In fact, it forms the basis for the all-knowing computer system seen in Purgatory.
In Aristoi, all human knowledge is contained within the Hyperlogos. The database is so big, in fact, that the Moon has been entirely converted into a dedicated server farm, and it's only one of many such farms throughout the known galaxy.
This is more or less how the wizard's manual works in the Young Wizards series. It's a constantly-updating collection of knowledge spanning most of the known universe and several others besides. Every wizard has a copy, in formats ranging from Spell Book to laptop to disembodied voice, and the contents rearrange themselves according to the wizard's needs and talents.
Live Action TV
CSI: Crime Scene Investigation is the king of the Omniscient Database. They have demonstrated databases on blood, hair, rope, wire, shoe prints, tire treads, tire rubber compositions, and even clown makeup patterns. There was a Lampshade Hanging in a sixth season episode, in which a character sarcastically suggested searching a database to discover the brand of a hot dog.
And yes, there is a national clown registry to prevent identical makeup.
Amusingly subverted in one episode where Greg is disappointed to learn that there is no hotdog database & winds up spending his entire year's food budget on various brands of hotdogs in an attempt to find a match to one found in a vic's stomach (He thought the department would re-imburse him. They didn't).
The software/database that allows one to find where a picture in New York was taken by measuring the skyline in comparison to a reference height (while the technique is sound, there is no such software).
In fact, it's when CSI avoids the trope that it can be jarring. A reoccurring scene is the local trace evidence guy naming a compound, and the CSI identifying the compound's common name, and its uses, including the more arcane (say, Jeweller grinder lubricant) on the top of their head. Said arcane use are always the key to cracking the case. This gets jarring because there ARE databases to identify the most common uses of chemicals.
There actually are multiple shoe-print databases available to police. An episode of Cold Case Files discussed a murder case that was solved, thanks to a partial shoe-print on a piece of glass that matched the shoes of a person in the neighborhood, who was found to be the killer.
The characters in CSI are also lucky that whatever sample of fabric or metal they find, there is always some unique element or polymer in it which is used by a single company in the world, and is located a short car drive away. Did we forget to mention that the magical database knows the exact 100% correct composition of everything you can buy?
Criminal Minds: Garcia, oh my God. It's hilarious. The team is like, "We need a list of every young, poorly adjusted white male who recently broke up with his girlfriend and has a mole on his upper left cheek." Garcia is like, "Oh, sure, I'll just check my database of who's dating whom and my mole-dar. Why not?" It borders on Self-Parody, as it is implied at several points during the series that Garcia can find anything.
An Omniscient Database is often an implicit background element of investigations in all the Law & Order series. Although they have used such databases for many of the same types of queries as in CSI: Crime Scene Investigation, the database query itself is more often carried out off-screen, with a lab analyst mentioning that a fiber found at the crime scene matches a luxury brand of purse that is only sold in only three stores in New York City.
On Law & Order: SVU, they often query some supposed national database implied to consist of all sex crime reports recorded by all local precincts throughout the entire country. They also have Warner, whose mind occasionally acts as a virtual Omniscient Database.
Star Trek: The franchise must hold the freakin' copyright on the Omniscient Database 'cause there are like 1500 of them in the series and movies.
The holodeck can recreate any setting or fictional story known to Man and several other species. (In one of the books, the holodeck can even replay every Opera performance from 1400 to the year 2356. How they managed to record pre-Renaissance operas... best not to ask.)
At one point, Picard commands the holodeck to recreate a specific date and time in a Parisian café, complete with accurate interactive portrayals of everyone who was present in the café at the time, in order to relive a memory on a whim. His subsequent disgust at himself for doing so clearly indicates this is not a holodeck program he'd built himself - the data already existed in the computer.
The Enterprise Main Computer carries all kinds of info like the launch codes to the Voyager probe built over 200 years earlier, or the command codes to every other Federation ship. And yet, when it would actually be useful for the computer to find a piece of obscure information, such as in 'The Naked Now' or 'Darmok', it takes hours. On the other hand, this matches real database performance - selecting a specific single record is far, far, FAR faster and easier than a complex query with plenty of cross-referencing, calculations on and parsing of retrieved data, and presumably multiple sources. 'Darmok' also contains more than a little Fridge Logic, in that the database actually knew the stories they were talking about, and yet nobody had made the link before.
Abby, the forensic scientist, tells us that her ex-boyfriend has made a database of databases after using a magic database of the measures of car fronts.
A database of turkey DNA comes in to play.
This trope was lampshaded with:
"Can you believe someone put together a database of grille dimensions?"
Torchwood's main characters are a secret organization with nationwide database records sorted by an ancient alien computer system. The team is capable of literally retconning anything by changing the database.
Torchwood also subverted it once - just as Jack and Toshiko are getting ready to search every database they have, Owen announces that he's already found the man they're looking for. He was listed in the phone book.
On Angel, Wolfram & Hart has access to several databases which actually are magical. Before Angel's team got access to these they used "Demons, Demons, Demons: The Demon Database".
Curiously averted, though, in a third-season episode in which Lilah Morgan has to dig through cabinets of files to find information on Angel.
Painkiller Jane: This is almost the entire purpose of Riley's character — to run the computers that have access to these things.
John Doe features a hero that displays ability of knowing everything that can be known about on earth. He's basically a walking and talking magical database.
Actually, he knows everything about everything except himself.
It might be more accurate to say that he has the internet in his head. For example, he doesn't know who Jack the Ripper was, but he knows all the theories on the subject.
And similar to John Doe, there's Kyle, from Kyle XY, who didn't know every trivial fact, only things like mathematical formulas. Well, until he spent a single day reading the World Book.
More literally, it is revealed that Kyle possesses the entire Zzyzx database in his mind.
Blake's 7: Orac, the super computer, who can read any computer with "tarial cells" and is therefore able to find any data the characters can possibly want. Whether he then tells them what he finds out is another story...
The Doctor is a living Omniscient Database. For more recent incarnations, there isn't a single episode in the new or old series where he met an alien, visited a planet, or saw a piece of technology he hadn't seen, invented, or met previously. In the new series, when a bunch of alien cops threaten him and Donna in a language not even the mighty TARDIS can translate he easily understands and berates them in the same language. The man is awesome. But then who knows what anybody might know after traveling the universe for a thousand years...
And then there's CAL, which contains every book ever written in any language, by any species,since the beginning of time. Including lost works. In both hard copy and digital.
The episode of the new series "Midnight" averts this somewhat. The 10th Doctor had no idea what the enemy was or how to fight it.
It's worth mentioning that he IS over nine hundred years old, and putting everything we've seen on-screen together would make about one-hundredth of his life.
Spooks - well, maybe it's magic, or maybe MI-5 really can do that stuff...
Chuck is a walking-talking database, able to identify terrorists on sight, however there is also such a database under the Orange Orange used by Sarah and Casey. In "Chuck vs. Santa Claus" we see it pulls up the record of "Ned" who has no criminal record, and is listed as having never been married or divorced. You know how powerful a computer is when it categorizes you by things you haven't done rather than by what you have done. Then again, it is a U.S. government computer...
It doesn't seem too farfetched since getting married in a legal sense requires a marriage license. And since in the US, being married grants several benefits in things like taxes, marital status is generally a standard appearance on many forms.
The Intersect and its legacy is in fact what drives the entire plot of Chuck. It's mere existence is what would destroy Chuck's family. Chuck's father created it, which would eventually force him into hiding. One of the earlier versions was later tested on his friend Hartley in order to implant a cover personality, but the personality took over, creating one of the most dangerous men in the world: the psychotic arms dealer Alexei Volkoff, who would later in fall in love with CIA agent Mary Bartowski, forcing her into an undercover assignment for decades and separating her from her family. To say nothing of what it did to Chuck, Ellie, and their friends and (other) family over the course of the series. Then again, it is a database that allows access to top secret information and several other skills such as martial arts, so there is a legitimate reason as to why people are after it.
Ziggy from Quantum Leap not only apparently has records of the minutiae of decades' worth of the day-to-day activities of pretty much everyone who was alive at the same time as Sam Beckett, but can also calculate the probability that Sam's interference in history will have the desired effect. And regardless of the percentage calculated, Ziggy is always right. Except for a couple episodes where despite an abnormally high percentage, Sam just "knows" he has to do something else. The times when Sam "knows" he has to do something else also are ones where all signs point to Al misleading or outright lying to Sam because of ulterior motives.
One episode has Hal using Ziggy to help Sam set up an ambush on a man walking around a corner, complete with a precise countdown. Apparently Ziggy has recordings of every human being's movements everywhere ever down to the second.
E-Ring had an example in the episode The General. Said general is kidnapped in Spain. In order to identify his kidnapper, the main character asks to consult the Voice Database of the Spanish Government (which apparently includes voice samples of each of the 40 million citizens of the country and is regularly updated to match voice changes due to aging, disease or plain mood swings), and then uses an experimental, American exclusive application to compare its files with the record of the kidnapper's voice he has. This leads to the obvious question of why on Earth would a government keep a voice database of all its citizens if it had no way of consulting it.
In an episode of Judging Amy, the DNA identifying computer with a database of known criminals returned a result of... cat DNA! Which actually justified. Its not that uncommon to stumble upon Animal DNA (Pets, Strays etc.) on a Crimescene so checking for the right number of chromosomes and some markers makes sense before you go onto a useless orgy of comparing datasets to a nonsensical sample.
An episode had Dexter identifying an STD in some bloodwork, then going into the Florida STD Database to find the names of people afflicted with that particular — and, of course, extremely rare—strain. It is implied that he never leaves the building during all of this, so Dexter's miraculous set of databases even cover what you might be doing with your genitals.
Subverted with Trinity. His DNA is collected halfway through the season but it can't be used to identify him because he has no criminal record and isn't in the database.
An episode of the Red Dwarf 2009 revival parodies this. After returning to Earth circa 2009, the guys from Red Dwarf find out that they are characters from a TV show by way of a video store showing the currently playing episode on their TVs. One salesman comments he never liked the show, and questions how a device Kryten is holding could know everything. Lister then asks the Kryten who the man is, which Kryten finds out from the device that he is "a pompous know-it-all, with a very small penis."
It does explain that it learns this by hacking into and reading his emails. Less magic database, more magic scanner.
Although the NYPD police detectives usually make do with a humble whiteboard and footwork, this trope is taken to hilariously ludicrous extremes in the two-parter "Tick... Tick... Tick..." / "Boom!" in which the FBI have smart boards so amazing that they gradually go from matching driver's license photos to witness sketches to being able to pinpoint the exact location of a hostage (down to the room she's being held in) thanks to a blurry image of what might be a bridge and the ambient noise of a subway.
It's memorably subverted in a first season episode, when Beckett says they'll need to look someone up in the missing persons' database- a bunch of paper folders.
The man from The Men in Black in one episode has a database in a suitcase. It instantly pinpoints a man's location by using his cellphone then automatically finds a Magical Security Camera in the area and maps a small part of the man's face onto a model, extrapolates the rest of his face from that, and pops up with an identity. Castle and Beckett are surprisingly unfazed by the technology.
David of Wishbone apparently has access to a database of dog breeds that includes things like their jaw measurements, for some reason. It has a very '90s aesthetic to it, like an over-the-top hacker-movie interface run on an old Macintosh OS.
Alcatraz has a database in their Bat Cave that can find, in seconds, a complete map of all private bomb shelters built in the 1960s by a company that went out of business decades ago.
While it generally avoided this sort of thing, there was once an episode of Babylon 5 where they were able to look up the name of the person living at a specific London address nearly 400 years earlier and also the fact that the person disappeared the day after the last Jack the Ripper murder.
Connor's magnum opus in Primeval is a database of the identifying traits of every dinosaur and other prehistoric animal known to man. It's just barely conceivable that Connor could have created such a thing single-handed if what he actually did was acquire copies of databases previously compiled by other researchers, tidy up and standardise the formatting and make them all searchable from a common web interface, but still rather unlikely.note Unless of course Connor was lying about doing it all by himself, which would be in-character for him in early Season 1. Accessing it on his laptop from just about anywhere without any apparent means of connecting to the Internet, on the other hand...
In Grand Theft Auto IV, the criminal dispatching minigame starts by looking up a perp from a stolen cop car's laptop. This gives an exact, updating location of the criminal for you to chase down.
ARI in Heavy Rain is connected in some way to the FBI database.
In Kingdom Hearts II, Sora seems to think that Ansem's computer is one of these. Because the computer belonging to the guy you killed last year will have info on where your friends are right now, right?
Patchouli Knowledge (It's in her name, duh!) of Touhou fame is an effective Human(oid) Magical Database, thanks to her centuries of study and self-made Great Big Library of Everything. In Subterranean Animism, she is capable of spilling out the histories and powers of every youkai Marisa meets in her adventure... with the slight problem of taking until after the yokai was defeated to look up any relevant information.
She also applied her knowledge to other tasks, such as constructing a spaceship from plywood, duct tape, and a whole lot of Functional Magic.
To push the point home, the only character who probably trumps her in intelligence might be Eirin Yagokoro, the Brain of the Moon. Very few humans know anything significant about the advanced Lunarian society and their technology (for their own protection, to some extent). In Silent Sinner In Blue, Patchouli not only makes remarkably accurate predictions regarding the timing of their rocket's flight to get to the Lunar Capital but she also immediately identifies the Lunar Veil, a Lunarian device that allows flawless travel between the Earth and Moon, that Eirin had covertly attached to the rocket. The ever-collected Eirin's first thought is stab this person now.
Uplink is a game basically built in databases, it features a Social Security Database, a Criminal Database and an Academic Database which store all the important people in the game and every life you'll ever need to ruin (including yours). And the Inter NIC, a database containing every public website in the world, which is to say a few hundred in the actual game.
From the Jem episode, "In Search of the Stolen Album": Synergy, Jem's super-computer, is able to scan clues that "Misfits"'s treasure hunt joke on the Holograms in a matter of moments—and even the reasons behind the places.
The FBI keeps records on all typewriter keys (Type that ransom note? They can tell what make and model), fingerprints (been arrested or served in the military?), paper (ransom note, etc.), bullets, mug shots, and many more things.
The National Crime Information Center (NCIC) is the United States' central database for tracking crime-related information. Since 1967, the NCIC has been maintained by the Federal Bureau of Investigation's Criminal Justice Information Services Division, and is interlinked with similar systems that each state maintains. Data is received from federal law enforcement agencies, state and local law enforcement agencies, as well as tribal law enforcement agencies, railroad police, and other agencies, such as state and federal motor vehicle registration and licensing authorities.
The United States Secret Service keeps records of every counterfeit US currency bill ever discovered, so they can match ones they find to see if it is a "new batch". Every written threat to the President (and other officials) is kept to see if the person has made a threat in the past.