DBMS中选择和投影之间的区别

先修课程–关系代数
1.选择：
此操作从满足选择语法中提到的给定条件的关系中选择元组的子集。

表示法–

σc (R)

在这里，“ c”是选择条件，“σ(西格玛)”用来表示选择运算符。

2.投影：
此操作选择某些必需的属性，同时放弃其他属性。

表示法–

πA (R)

其中“ A”是属性列表，它是Relation(R)的属性中所需的一组属性，
符号“π(pi)”用于表示Project运算符，
R通常是一个关系代数表达式，它导致一个关系。

DBMS中选择和投影之间的区别

S. No.	Category	Selection	Projection
1.	Other Names	The selection operation is also known as horizontal partitioning.	The Project operation is also known as vertical partitioning.
2.	Use	It is used to choose the subset of tuples from the relation that satisfies the given condition mentioned in the syntax of selection.	It is used to select certain required attributes, while discarding other attributes.
3.	Partitioning	It partitions the table horizontally.	It partitions the table vertically.
4.	Which used first	The selection operation is performed before projection (if they are to be used together).	The projection operation is performed after selection (if they are to be used together).
5.	Operator Used	Select operator is used in Selection Operation.	Project operator is used in Projection Operation.
6.	Operator Symbol	Select operator is denoted by Sigma symbol.	Project operator is denoted by Pi symbol.
7.	Commutative	Selection is commutative.	Projection is not commutative.
8.	Column Selection	Select is used to select all columns of a specific tuple.	Project is used to select specific columns.
9.	SQL Statements used	SELECT, FROM, WHERE	SELECT, FROM