From (SQL) explained

The SQL From clause is the source of a rowset to be operated upon in a Data Manipulation Language (DML) statement. From clauses are very common, and will provide the rowset to be exposed through a Select statement, the source of values in an Update statement, and the target rows to be deleted in a Delete statement. ^[1]

FROM is an SQL reserved word in the SQL standard. ^[2]

The FROM clause is used in conjunction with SQL statements, and takes the following general form:

SQL-DML-Statement FROM table_name WHERE predicate

The From clause can generally be anything that returns a rowset, a table, view, function, or system-provided information like the Information Schema, which is typically running proprietary commands and returning the information in a table form.^[3]

Examples

The following query returns only those rows from table mytable where the value in column mycol is greater than 100.

SELECT *FROM mytableWHERE mycol > 100

Requirement

The From clause is technically required in relational algebra and in most scenarios to be useful. However many relational DBMS implementations may not require it for selecting a single value, or single row - known as DUAL table in Oracle database.^[4] SELECT 3.14 AS PiOther systems will require a From statement with a keyword, even to select system data.^[5] select to_char(sysdate, 'Dy DD-Mon-YYYY HH24:MI:SS') as "Current Time"from dual;

Notes and References

1. Web site: From clause in Transact SQL.
2. Web site: Reserved Words in SQL.
3. Web site: System Information Schema Views (Transact-SQL) .
4. Web site: Selecting from the DUAL Table.
5. Web site: Oracle Dates and Times.