Business data is usually stored in relational databases, where it persists for use by enterprise applications. Applications use SQL, typically embedded within a programming language, to store and retrieve the data.
Today data exists everywhere. You can find it in databases and big data clusters, in branch offices or manufacturing devices, in ATMs, in cars, trucks, and in sensors. The typical enterprise may have hundreds of different data sources containing the valuable data you need.
I searched for the manual which would explain how to write proper SQL. I never found it and the more I talked to people on which strategy I should follow, the less useful information I seemed to get. The same was true whenever I asked for general rules to decide which index was needed.
DB2 is particularly good at running complex query and analytical processing. Since all modern hardware contains multiple cores and CPUs, and many systems are composed of multiple machines, it is critical that DB2 run individual queries across all available computing resources.