A Relation is a logical data structure composed of
The following data structure are a relation:
It also model either:
but not both.
In the SQL Iso, a relation is a collection of zero or more rows where each row is a sequence of one or more column values.
A relation is a bag (multiset) of tuple (ie data with possible different sql data type by column). It's not precisely a set because a set does not allow duplicate whereas a multiset (bag) does.
The schema of a relation is its name and columns along with all attributes such as data type. Because the schema is stored as relation, you can query it.
More .. a SQL - Schema (Metadata).
We say that R1 = R2 if and only if we can guarantee that the bag of tuples (rows) produced by R1 is the same as the bag of tuples produced by R2.
Logical:
Spark DataFrame is a distributed collection of data organized into named columns
Example:
people.col("age").plus(10); // in Java
Data Frame Panda (API) is a 2-dimensional labeled data structure with columns of potentially different types.
You can think of it like a spreadsheet or SQL table, or a dict of Series objects.
DataFrame accepts many different kinds of input:
A data frame (doc), a matrix-like structure whose columns may be of differing types (numeric, logical, factor and character and so on).
A data frame is a collection of data organized into named columns from differents data type.
In java\client\org\apache\derby\client\am\Cursor.java, they hold the data in byte array.
//-------------Structures for holding and scrolling the data -----------------
public byte[] dataBuffer_;
public ByteArrayOutputStream dataBufferStream_;
public int position_; // This is the read head
public int lastValidBytePosition_;
public boolean hasLobs_; // is there at least one LOB column?
// Current row positioning
protected int currentRowPosition_;
private int nextRowPosition_;
// Let's new up a 2-dimensional array based on fetch-size and reuse so that
protected int[] columnDataPosition_;
// This is the actual, computed lengths of varchar fields, not the max length from query descriptor or DA
protected int[] columnDataComputedLength_;
// populate this for
Engine: