Oracle 'Partition By' and 'Row_Number' keyword

sql

prompt-engineering

join

deduplication

byAlex Kataev·Dec 31, 2024

The ROW_NUMBER() beast, when tamed with PARTITION BY in Oracle SQL, grants a magnificently sequenced order within groups:

SELECT col1, col2, 
       ROW_NUMBER() OVER (PARTITION BY col1 ORDER BY col2) AS seq
FROM my_table;

Here, the seq column assigns a unique number to each row within groups formed by col1, sorted by col2.

Making sense of sequences

Going for an analytical home run? Connect your ROW_NUMBER() pitch with an ORDER BY bat. This combination is crucial, particularly when non-unique combinations are in play. Missing out on ORDER BY is like forgetting your parachute when skydiving—dangerous! It may lead Oracle to assign sequence numbers in a chaotic and unanticipated way, throwing your analysis off-balance.

Navigating the sea of similarity

When similar data sings the same tune and lacks any evident sorting criteria, consider using a GUID (Globally Unique Identifier) as your compass. This approach assures that sequence numbers are given in a consistent and unchanging order. Feel like Columbus yet?

Preventing random skewing

Non-unique partitions can act like puzzles, throwing identical numbers here and there. Don't let it mess up your mojo! Steer clear of randomness and ensure your PARTITION BY sails with a ORDER BY wind, making your numbers predictable and data analysis smoother than smoothie.

Banishing duplicates

We all love multiplex, but seeing the same movie again and again? Nah! Here's a trick to eliminate duplicates by teaming up PARTITION BY, ROW_NUMBER(), and a smart filter:

SELECT col1, col2
FROM (
  SELECT col1, col2, 
         ROW_NUMBER() OVER (PARTITION BY col1 ORDER BY col2) AS rn -- removes duplicates faster than you can say 'duplicate'
  FROM my_table
) 
WHERE rn = 1; -- Only invites unique guests to the party

The wide use-case universe

Application in ranking, pagination, and deduplication

PARTITION BY coupled with ROW_NUMBER(): a mighty team! Whether you need to rank records, implement smart pagination, or deduplicate your galaxy of data, this dynamic duo has got your back.

Catering to database rules

Like the different dialects of English, SQL dialects have their quirks too. Some databases might throw a tantrum with PARTITION BY and no ORDER BY. Validate your queries against your SQL dialect's rulebook to avoid surprises.

Cherry-picking the 'order'

Throw some brain fuel into the computation machine, always! Consider the context of data and your analysis quests before choosing the ORDER BY criteria. It's more about conveying tales of insight with your data, rather than just maintaining consistency.

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