From (SQL)

The FROM clause in SQL defines the use of one or more tables in a query. As a reserved word in the SQL standard , the general form of a query is:

SELECT Spaltenname FROM Tabellenname [WHERE Bedingung]

The FROMclause specifies the tables for rows to be deleted within delete statements and defines the tables for queries in subqueries of update statements. Tables , views or information schemes (general database information) form the basis for the FROMclause.

Examples

Output only rows of the table myTable with column values ​​of myColumn greater than 100:

SELECT *
FROM   meineTabelle
WHERE  meineSpalte > 100

Remove all entries from the Trees table with a height less than 80.

DELETE FROM Bäume
 WHERE Höhe < 80;

Use the FROMclause in a subquery (also called a subquery) to define the conditions for selecting rows to be changed:

UPDATE T1
   SET C1 = 2
 WHERE C2 IN ( SELECT C3
                 FROM T2
                WHERE C4 = 0)

Database operations without FROM

Some DBMS do FROMnot need the clause to return a single value or line. In database system from Oracle this works for. B. via the so-called DUAL table:

SELECT 3.14 AS Kreiszahl

However, other systems also require a key word (also called a keyword) to select the relevant data:

SELECT to_char(sysdate, 'Dy DD-Mon-YYYY HH24:MI:SS') as "Aktuelle Zeit"
FROM dual;

In Sybase, the output of global variables such as the version used does not require a FROMclause:

SELECT @@version

A UPDATEstatement without a subquery does not need a FROMclause:

UPDATE t1 SET col1 = col1 + 1

See also

• Data manipulation language (DML)

Individual evidence

1. ^ Microsoft : From clause in Transact SQL. Retrieved December 3, 2018 . 
2. ↑ Drupal : Reserved Words in SQL. Retrieved December 3, 2018 . 
3. ^ Microsoft : System Information Schema Views (Transact-SQL). Retrieved December 3, 2018 . 
4. ^ Oracle : Selecting from the DUAL Table. Retrieved December 3, 2018 . 
5. ↑ Infolab Stanford University : Oracle Dates and Times. Retrieved December 3, 2018 . 
6. ↑ Sybase : Sybooks Online: Chapter 2: SQL Language Elements: Global variables. Retrieved December 3, 2018 . 
7. ^ MySQL : UPDATE syntax. Retrieved December 3, 2018 .