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High-cardinality refers to columns with values that are very uncommon or unique. High-cardinality column values are typically identification numbers, email addresses, or user names. An example of a data table column with high-cardinality would be a USERS table with a column named USER_ID. This column would contain unique values of 1-n. Each ...
The distinct values are stored in a string intern pool. The single copy of each string is called its intern and is typically looked up by a method of the string class, for example String.intern() [2] in Java. All compile-time constant strings in Java are automatically interned using this method. [3]
In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.
In situations where the number of unique values of a column is far less than the number of rows in the table, column-oriented storage allow significant savings in space through data compression. Columnar storage also allows fast execution of range queries (e.g., show all records where a particular column is between X and Y, or less than X.)
An Item in DynamoDB is a set of attributes that can be uniquely identified in a Table. An Attribute is an atomic data entity that in itself is a Key-Value pair. The Key is always of String type, while the value can be of one of multiple data types. An Item is uniquely identified in a Table using a subset of its attributes called Keys. [7]
For example, {Monarch Name, Royal House} cannot be a superkey because for the same attribute values (Edward, Plantagenet), there are two distinct tuples: (Edward, II, Plantagenet) (Edward, III, Plantagenet) Finally, after elimination, the remaining sets of attributes are the only possible superkeys in this example:
MySQL (/ ˌ m aɪ ˌ ɛ s ˌ k juː ˈ ɛ l /) [6] is an open-source relational database management system (RDBMS). [6] [7] Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, [1] and "SQL", the acronym for Structured Query Language.
From Java 8 onwards, the default keyword can be used to allow an interface to provide an implementation of a method. do The do keyword is used in conjunction with while to create a do-while loop, which executes a block of statements associated with the loop and then tests a boolean expression associated with the while.