What is the function of from in sql

The role of the FROM clause in SQL is to specify the data source, including: retrieving data from one or more tables, establishing association conditions between tables, and combining the WHERE clause to filter data

Purpose of FROM clause in SQL

In SQL, FROM clause is used to specify the table or view from which data is to be retrieved. It is an essential clause in the SELECT statement because it defines the data source.

Function

The main function of the FROM clause is:

• Specify the data source:It tells SQL to interpret The table or view from which the server retrieves data.
• Retrieve data from multiple tables: It allows retrieving data from multiple tables, performing data associations and unions.
• Set association conditions: It can be used in conjunction with the ON or USING clause to establish association conditions between multiple tables.
• Filtering data: When the FROM clause is used in conjunction with the WHERE clause, it can filter the data from the data source and only return rows that meet certain conditions.

Syntax

The syntax of the FROM clause is as follows:

<code>FROM table_name [alias] [, table_name [alias]] ...</code>

• table_name: To retrieve from The name of the table of data.
• alias: Optional alias for the table, which can simplify table references.

Example

The following example retrieves all customer data from a table named "customers":

<code>SELECT * FROM customers;</code>

The following example retrieves all customer data from "customers" "Retrieve customer and order data from the "orders" table and use the aliases "c" and "o":

<code>SELECT * FROM customers c, orders o;</code>

In summary, the FROM clause is a key clause in SQL that is used to specify the data source , relate tables and filter data to retrieve the required data from the database.

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