If it refers to a deterministic user-defined function, it cannot be used as a partitioning key column.It can only refer to columns defined in the same table.It cannot refer to another virtual column by name.The expression used in the virtual column definition has the following restrictions:.Virtual columns are not supported for index-organized, external, object, cluster, or temporary tables.The result cache must be flushed if cached queries have accessed the virtual column.Materialized views that access the virtual column must be fully refreshed.Indexes on the virtual column must be rebuilt.Constraint on the virtual column must be disabled and re-enabled.In such cases the following steps must be taken after the function is recompiled: Functions in expressions must be deterministic at the time of table creation, but can subsequently be recompiled and made non-deterministic without invalidating the virtual column.Tables containing virtual columns can still be eligible for result caching.Virtual columns can be referenced in the WHERE clause of updates and deletes, but they cannot be manipulated by DML.Indexes defined against virtual columns are equivalent to function-based indexes.Notes and restrictions on virtual columns include: Select column_id, column_name, virtual_column, data_defaultĬOLUMN_ID COLUMN_NAME VIRTUAL_COLUMN DATA_DEFAULTĤ PRICE_WITH_TAX YES ROUND("PRICE"*1.2,2) We can see the PRICE_WITH_TAX column is marked as a virtual column, and the DATA_DEFAULT column displays the expression used to derive the value. The _TAB_COLS views includes columns called VIRTUAL_COLUMN and DATA_DEFAULT. When we query the table, the PRICE_WITH_TAX column reflects the change.Īlter table t1 drop column price_with_tax DROP COLUMN command, then add a new virtual column to the existing table using the ALTER TABLE. We drop the virtual column using the ALTER TABLE. We'll change the tax back to 20% using a different method. When we query the table, the PRICE_WITH_TAX column reflects the change. Notice we don't include any of the optional keywords. In the following example we increase the tax to 30%. We can alter the virtual column expression using the ALTER TABLE MODIFY command. There is an example of adding a virtual column to an existing table below. We query the table, and we can see the PRICE_WITH_TAX column displays the correct value. Insert into t1 (id, product, price) values (2, 'bike', 1000) Insert into t1 (id, product, price) values (1, 'computer', 1500) Notice we've not referenced the PRICE_WITH_TAX column. We describe the table, and the PRICE_WITH_TAX column looks like a normal column. Price_with_tax number(10,2) generated always as (round(price*1.2,2)) virtual The expression can include functions, but it must be deterministic. In this case we've increased the price value by 20%, and rounded the result to 2 decimal places. It includes a virtual column to display the price with tax included. The script below creates and populates a table to hold products. The GENERATED ALWAYS and VIRTUAL keywords are options, and provided for clarity only. If the datatype is omitted, it is determined based on the result of the expression. The syntax for defining a virtual column is listed below.Ĭolumn_name as (expression)
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