Increment Row Number on Group

Shake hands with DENSE_RANK()

Now, what if you want to spin the wheel and increment the row number only when there's a change in a specific column? A different drummer beats for it - it's called DENSE_RANK().

SELECT
  shade, -- imagine this is the category deciding the drumbeat of the row number increment
  DENSE_RANK() OVER(ORDER BY shade) AS t_index -- our drummer
FROM
  YourTable;


The beauty of t_index here is that it only rolls up when a unique shade value surfaces, else it retains the status quo. No worries about the repetition of the shade values!

Cooking custom row numbers

Let's spice things up! Suppose you want a unique index within each shade group and a sequential index (s_index) counting rows in the entire result set. Get the best of both worlds with a blend of ROW_NUMBER() and DENSE_RANK().

SELECT
  shade,
  t_index,
  ROW_NUMBER() OVER(PARTITION BY shade ORDER BY YourOrderColumn) AS s_index -- spices up a unique count within the shade
FROM (
  SELECT
    *,
    DENSE_RANK() OVER(ORDER BY shade) AS t_index -- preserves the count, kicking it up a notch only with a change in shade!
  FROM YourTable
) AS SubQuery;


When gaps creep in

Sometimes life, or sequential numbering rather, comes with gaps - courtesy to deleted records. Opt for a dynamo like a CTE (Common Table Expression) or a subquery in such cases to reinstate order:

WITH RankedTable AS (
  SELECT
    *,
    ROW_NUMBER() OVER(PARTITION BY shade ORDER BY YourOrderColumn) AS s_index
  FROM YourTable
)
SELECT
  *,
  DENSE_RANK() OVER(ORDER BY s_index) AS t_index -- Voila! A seamless sequence irrespective of the initial gaps
FROM RankedTable;


Efficiency to the rescue!

An efficient sort performance especially with a behemoth dataset, subtracts I/O operations. You can live this dream with indexed views or materialized views enabling the precalculation of rankings.

CREATE MATERIALIZED VIEW YourView AS
SELECT
  *,
  ROW_NUMBER() OVER(PARTITION BY shade ORDER BY YourOrderColumn) AS s_index, -- What's cooking? A sizzling unique count within the shade...
  DENSE_RANK() OVER(ORDER BY shade) AS t_index -- ...tossed with a well-preserved count, incrementing only with a shade change!
FROM
  YourTable; -- Hungry for data, are we?


Wrestling with complexities

For the braver ones grappling with severe scenarios like distributed databases, replication lags, or concurrency issues, consider isolation levels and transaction strategies. It's like weaving a safety net with temporary tables, locking mechanisms, or sometimes even application-level logic to ensure safe and consistent numbering.

Practical takeaways

"Practice, practice, practice!" - as the inspirational SQL fortune cookie says. Before you crack on with your hakuna matata coding spree, here are some snacks for thought:

• ROW_NUMBER() is your faithful friend for unique, incremental counting.
• Dial DENSE_RANK() for maintaining ranks across gaps.
• Why not marry the two functions for customised grouping and sequencing?
• Indexed views or materialized views are your chariots for better performance.
• Think on your feet and adapt advanced SQL and DB tactics to overcome complexities. Coding is not a cookie-cutter job but about making the cookie fit the problem!