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10 Unique Spark SQL Features You Won't Find in Oracle

Apache Spark and Oracle Database are both powerful platforms, but Spark offers several features that Oracle does not natively support. These unique features stem from Spark's distributed architecture and rich SQL API.

Below, we explore 10 exclusive capabilities of Spark SQL with sample datasets, examples, and use cases to help readers understand their practical applications.

I have used these features in my daily life, and I thought it would be helpful to share what I've learned.


1. Anti Join

Use Case

Quickly filter out rows that have matching records in another table, such as identifying users who have not completed a specific action in an activity log.

Sample Dataset:

table_a:
| id |
|----|
| 1 |
| 2 |
| 3 |

table_b:
| id |
|----|
| 2 |

Spark Query:

SELECT a.*
FROM table_a a
LEFT ANTI JOIN table_b b
ON a.id = b.id;
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Result:
| id |
|----|
| 1 |
| 3 |

Oracle Equivalent:

SELECT a.*
FROM table_a a
WHERE NOT EXISTS (
    SELECT 1 FROM table_b b WHERE a.id = b.id
);
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2. from_unixtime Function

Use Case

Converting timestamps for human-readable reports, especially in IoT or log analytics where data is stored as Unix timestamps.

Sample Dataset:

UNIX Timestamp:
| timestamp |
|----------------|
| 1700000000 |

Spark Query:

SELECT from_unixtime(1700000000) AS readable_date;
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Result:
| readable_date |
|-------------------|
| 2023-11-14 02:53:20 |

Oracle Equivalent:

SELECT TO_CHAR(TO_DATE('1970-01-01', 'YYYY-MM-DD') + NUMTODSINTERVAL(1700000000, 'SECOND'), 'YYYY-MM-DD HH24:MI:SS') AS readable_date
FROM dual;
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3. Explode

Use Case

Flattening arrays for detailed analytics, such as extracting product details from an array of purchased items.

Sample Dataset:

table:
| id | array_col |
|----|----------------|
| 1 | ["A", "B"] |
| 2 | ["C", "D"] |

Spark Query:

SELECT id, explode(array_col) AS value
FROM table;
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Result:
| id | value |
|----|-------|
| 1 | A |
| 1 | B |
| 2 | C |
| 2 | D |

Oracle Equivalent:

SELECT id, column_value AS value
FROM table, TABLE(CAST(array_col AS TABLE_TYPE));
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4. Map from Arrays

Use Case

Creating key-value pairs dynamically for use in aggregation or lookups, such as storing user preferences or configurations.

Sample Dataset:

table:
| id | keys | values |
|----|------------|--------------|
| 1 | ["k1", "k2"] | ["v1", "v2"] |

Spark Query:

SELECT id, map_from_arrays(keys, values) AS key_value_map
FROM table;
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Result:
| id | key_value_map |
|----|-----------------------------|
| 1 | {"k1": "v1", "k2": "v2"} |

Oracle Equivalent: Not directly supported. Requires JSON or PL/SQL.


5. Approximate Count Distinct

Use Case

Efficiently estimating the number of unique users or items in massive datasets, such as tracking active users in real-time.

Sample Dataset:

events:
| user_id |
|---------|
| 1 |
| 2 |
| 2 |
| 3 |
| 4 |
| 5 |
| 5 |
| 6 |

Spark Query:

SELECT approx_count_distinct(user_id) AS unique_users
FROM events;
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Result:
| unique_users |
|--------------|
| 6 |

Oracle Equivalent:

SELECT COUNT(DISTINCT user_id) AS unique_users
FROM events;
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6. Flattening Nested Data Structures

Use Case

Simplifying hierarchical or nested data for downstream consumption, such as processing JSON data into relational tables.

Sample Dataset:

table:
| nested_struct |
|--------------------------|
| {"col1": "A", "col2": "B"} |

Spark Query:

SELECT nested_struct.col1, nested_struct.col2
FROM table;
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Result:
| col1 | col2 |
|------|------|
| A | B |

Oracle Equivalent: Not directly supported. Requires PL/SQL.


7. Lateral View with Explode

Use Case

Extracting and analyzing individual elements of arrays stored in tables, such as breaking down multi-valued columns for visualization.

Sample Dataset:

table:
| id | array_col |
|----|----------------|
| 1 | ["A", "B"] |
| 2 | ["C", "D"] |
| 3 | ["E", "F"] |

Spark Query:

SELECT id, value
FROM table
LATERAL VIEW explode(array_col) exploded_table AS value;
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Result:
| id | value |
|----|-------|
| 1 | A |
| 1 | B |
| 2 | C |
| 2 | D |
| 3 | E |
| 3 | F |

Oracle Equivalent:

SELECT id, column_value AS value
FROM table, TABLE(CAST(array_col AS TABLE_TYPE));
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8. Map from Entries

Use Case

Converting arrays of key-value pairs into a map structure, useful in cases where the data is stored in pair form and needs to be queried or aggregated as a map.

Sample Dataset:

table:
| id | key_value_pairs |
|----|----------------------------------|
| 1 | [("k1", "v1"), ("k2", "v2")] |
| 2 | [("k3", "v3"), ("k4", "v4")] |

Spark Query:

SELECT id, map_from_entries(key_value_pairs) AS key_value_map
FROM table;
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Result:
| id | key_value_map |
|----|-----------------------------|
| 1 | {"k1": "v1", "k2": "v2"} |
| 2 | {"k3": "v3", "k4": "v4"} |

Oracle Equivalent: Not directly supported.


9. Higher-Order Functions (Transform)

Use Case

Applying complex transformations to arrays within queries, such as scaling numerical data or normalizing values.

Sample Dataset:

table:
| id | array_col |
|----|--------------|
| 1 | [1, 2, 3] |
| 2 | [4, 5, 6] |

Spark Query:

SELECT id, transform(array_col, x -> x * 2) AS doubled_values
FROM table;
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Result:
| id | doubled_values |
|----|-------------------|
| 1 | [2, 4, 6] |
| 2 | [8, 10, 12] |

Oracle Equivalent: Not supported directly. Requires PL/SQL.


10. Union with Schema Evolution

Use Case

Merging datasets with schema differences, such as integrating data from multiple sources during ETL processes.

Sample Dataset:

table_a:
| id | name |
|----|---------|
| 1 | Alice |
| 3 | Charlie |
| 5 | Eve |

table_b:
| id | full_name |
|----|-----------|
| 2 | Bob |
| 4 | Diana |
| 6 | Frank |

Spark Query:

SELECT id, name
FROM table_a
UNION BY NAME
SELECT id, full_name AS name
FROM table_b;
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Result: Combines data with schema alignment.
| id | name |
|----|---------|
| 1 | Alice |
| 2 | Bob |
| 3 | Charlie |
| 4 | Diana |
| 5 | Eve |
| 6 | Frank |

Oracle Equivalent: Not supported directly. Requires manual schema alignment.


Feel free to share your thoughts or insights. I'm excited to learn and grow together with you.

Happy Learning!

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