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.
FROM is an SQL reserved word in the SQL standard.
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,"/system-provided information like the Information Schema, which is typically running proprietary commands. And returning the "information in a table form."
Examples※
The following query returns only those rows from table mytable where the value in column mycol is greater than 100.
SELECT * FROM mytable WHERE 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 single value. Or single row - known as DUAL table in Oracle database.
SELECT 3.14 AS Pi
Other systems will require a From statement with a keyword, even to select system data.
select to_char(sysdate, 'Dy DD-Mon-YYYY HH24:MI:SS') as "Current Time" from dual;