Table of Contents
Why do we persist a computed column?
Marking a computed column as PERSISTED allows an index to be created on a computed column that is deterministic, but not precise. For more information, see Indexes on Computed Columns. Any computed columns used as partitioning columns of a partitioned table must be explicitly marked PERSISTED.
Are there any disadvantages of using computed column?
Some Limitations. You can not reference columns from other tables for a computed column expression directly. You can not apply insert or update statements on computed columns.
What is persisted SQL?
When you create a computed column in SQL Server, you have the option of flagging it as “persisted”. A persisted computed column is one that is physically stored in the table. If you don’t specify that it’s persisted, then the column’s value will be calculated each time you run a query against it.
What is computed column in SQL Server?
A computed column is a virtual column that is not physically stored in the table, unless the column is marked PERSISTED. A computed column expression can use data from other columns to calculate a value for the column to which it belongs.
What is a persisted computed column?
Computed columns can be persisted. It means that SQL Server physically stores the data of the computed columns on disk. When you change data in the table, SQL Server computes the result based on the expression of the computed columns and stores the results in these persisted columns physically.
Can we create index on computed column?
You can define indexes on computed columns as long as the following requirements are met: Ownership requirements. Determinism requirements. Precision requirements.
What is persist table?
A persistent staging table records the full history of change of a source table or query. The source could a source table, a source query, or another staging, view or materialized view in a Dimodelo Data Warehouse Studio (DA) project. In a persistent table, there are multiple versions of each row in the source.
Can a computed column be a foreign key?
If we mark a computed column as persisted, we can define constraints such as Check, Not NULL, or Foreign key. It also allows you to define an index for the persisted computed column.
What is persisted computed column?
Persisted computed columns It means that SQL Server physically stores the data of the computed columns on disk. When you change data in the table, SQL Server computes the result based on the expression of the computed columns and stores the results in these persisted columns physically.