I read again Celko book 3 Tables 3.3 Computed Columns about SQL and for the author the main work is done on the DDL (Data definition language) to compute metadata so not the data store in table but how those data are manage ( restriction , constraint ) . I think Computed columns should be use on online SQL engine in commercial web site. I think because most of the time the complexity of relationship beetween tables is hidden by use php DAL ( Data Layer Abstraction ) layer on the Back End side of CMS.
DAL name could be for ADOdb, Pear DB for php , ezSQL for wordpress , JFactory for joomla ,Drupal Abstraction Layer from 4 to 8 , web2py/Web3py for python/GAE and ZODB for Zope/plone ....
this make me think if i don't do mistake that active column already exist in SQL Dialect ( don't know wich )
< column name > < data type > [GENERATED ALWAYS] AS (< expression >) [VIRTUAL | PERSISTENT]
< column name > < data type > [COMPUTED] BY (< expression >)
CREATE TABLE Order_Details (order_nbr CHAR(15) NOT NULL REFERENCES Orders(order_nbr),
gtin CHAR(15) NOT NULL,
PRIMARY KEY (order_nbr, gtin),
order_qty INTEGER NOT NULL,
unit_price DECIMAL(10,2) NOT NULL,
line_tot DECIMAL(15,2) GENERATED ALWAYS AS (order_qty * unit_price) VIRTUAL );
I think the best way is to find functionalities support by SQL9 engine is to use the input filter of the QueryBuilder . At this time the word GENERATED , ALWAYS, VIRTUAL/ STORED return nothing .
should the active column in mfd9 when appear ll have to trigger update when change occur ?
This concept ( wiki , theory) are supported since specific version number ( year) in some database under different name :
---maria db 5.2 (2010)/ 10.1 ........=> virtual column
---MySQL 5.17.6 (2xxx) /5.7.21. ....=> generated columns
---SQLServer 2008(2008)...............=> Computed Columns
---FireBird 2.1(2014) /3.0.2..=> Computed Columns
---Manifold 8 .................................=> Active Columns
---postgresql ( no support ) ...........=> trick1
---oracle ( No support ) .................. => trick use BEFORE INSERT TRIGGER
Hope this ll give another point of view of active column in manifold 8 .
"Because my dad promised me" ( interstellar ) but blackhole don't exist
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