From (SQL)

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   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 a single value, or single row - known as DUAL table in Oracle database.[4] 

SELECT 3.14 AS Pi

Other 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;

References

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

Content Disclaimer

Informasi ini disarikan dari Wikipedia dan disajikan kembali untuk tujuan edukasi. Konten tersedia di bawah lisensi CC BY-SA 3.0. Kami tidak bertanggung jawab atas ketidakakuratan data yang bersumber dari kontribusi publik tersebut.

  1. The information displayed on this website is sourced in part or in whole from Wikipedia and has been adapted for the purpose of restating it. We strive to provide accurate and relevant information, however:
  2. There is no guarantee of absolute accuracy. Wikipedia is an open, collaborative project that can be edited by anyone, so information is subject to change.
  3. It is not intended to constitute professional advice. The content displayed is for informational and educational purposes only. For important decisions (e.g., medical, legal, or financial), please consult a professional.
  4. Content copyright. Wikipedia is licensed under the Creative Commons Attribution-ShareAlike License (CC BY-SA). This means that content may be reused with appropriate attribution and shared under a similar license.
  5. Responsible use. Any risk arising from the use of information from this website is entirely the responsibility of the user.