Update "Computed Columns" page with examples of new multi-region columns and syntax

[rmloveland]

Richard Loveland (rmloveland) commented:

The Computed Columns page has an old skool partitioning example that is superseded by the new v21.1+ multi-region capabilities. However, computed columns can still be used with the new abstractions, as shown below.

Examples courtesy @rytaft in discussion on #10280.

-- This creates a computed column with the name cr.
CREATE TABLE t (
  id INT PRIMARY KEY,
  cr crdb_internal_region AS (
      CASE
        WHEN id <= 10 THEN 'us-east-1'
        ELSE 'ap-southeast-2'
      END
    ) STORED
) LOCALITY REGIONAL BY ROW AS "cr";

-- This creates a computed column with the the default name of `crdb_region`,
-- so there's no need to identify it with "AS".
CREATE TABLE t (
  id INT PRIMARY KEY,
  crdb_region crdb_internal_region AS (
      CASE
        WHEN id <= 10 THEN 'us-east-1'
        ELSE 'ap-southeast-2'
      END
    ) STORED
) LOCALITY REGIONAL BY ROW;

Jira Issue: DOC-1626

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[rytaft]

I believe this is still relevant.