The phrase "a database of millions" is correct and usable in written English.
It can be used when referring to a collection of data that contains millions of entries or records.
Example: "The research team accessed a database of millions to analyze trends in consumer behavior."
Alternatives: "a repository of millions" or "a collection of millions".
He oversaw the creation of the campaign's $90 million digital operation, including a database of millions of Trump supporters, which was developed by a Texas business that had previously worked on the Trump Organization website.
Google has found a way to weave the display advertising into its existing automated auction, which selects ads for any given page from a database of millions of potential advertisements from hundreds of thousands of marketers.
In the United States, a library cooperative in Ohio grew into the OCLC Online Computer Library Center, a not-for-profit company with a database of millions of catalog records to which libraries can purchase access.
Within months, Kogan and Cambridge Analytica had a database of millions of US voters that had its own algorithm to scan them, identifying likely political persuasions and personality traits.
This is the latest in a long line of data breaches that includes the recent TalkTalk hacks, which saw a database of millions of customers being accessed by hackers, leading to phishing attacks and scams.
Last July, the House narrowly failed to pass an amendment to the defense spending bill offered by Rep. Justin Amash (R-Mich). that would have barred the NSA from amassing a database of millions of Americans' telephone calls for counterterrorism purposes.
Last year, companies claimed they could compare live feeds to a database of billions of faces.
Indigo has built a database of tens of thousands of individual microbes isolated from crops that thrive under harsh conditions.
WikiLeaks released a database of thousands of Clinton's emails in March that year, obtained through a freedom of information request.
A team led by Markus Schläpfer of the Massachusetts Institute of Technology in Cambridge used a database of billions of telephone calls from Portugal and the United Kingdom to measure social connectivity.
So far, Dima has helped to build a database of hundreds of thousands of small molecules and proteins, detailing their chemical structures and binding properties.
