The role of from in sql

The FROM clause in SQL is used to specify the data source of the query, including: Specify the data source: define the table or view to be queried. Join tables: Combine data from multiple tables into a query using the JOIN keyword. Set query scope: retrieve only data in the specified table or view.

The role of FROM clause in SQL

The FROM clause in SQL is used to specify the Get the table or view of the data. It is required in the SELECT statement because it defines the data source.

Function:

• Specify the data source: The FROM clause specifies the name of the table or view to be queried. You can specify multiple data sources at once to retrieve data from them.
• Join tables: The FROM clause can also be used to join tables, that is, to combine data from multiple tables in a query. This can be achieved by using the JOIN keyword.
• Set query scope: The FROM clause limits the scope of the query and only obtains data in the specified table or view.

Syntax:

<code>SELECT column_list
FROM table_name</code>

Where:

• column_list is the list of columns to retrieve.
• table_name is the name of the table or view to be queried.

Example:

<code class="sql">SELECT *
FROM customers;</code>

This query retrieves all columns from the table named "customers".

Join tables:

<code class="sql">SELECT *
FROM orders
INNER JOIN products
ON orders.product_id = products.id;</code>

This query retrieves data from the "orders" table and the "products" table and joins these based on the "product_id" column using the ON clause Two tables.

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