How to iterate over results of a query

Diving deeper into cursors

Cursors are great to deal with row-by-row operations, yet they might be resource-heavy and not the most efficient way to handle data iterations for huge datasets.

'A Need for Speed': Batch data insertion

Got stuck with INSERT operations within a loop? Say no more! Use a single INSERT INTO...SELECT:

INSERT INTO TargetTable (Column1, Column2)
SELECT Column1, Column2
FROM SourceTable
WHERE YourConditions; 
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Oh look, all inserts done in a single query! Need for speed, anyone? 🚀

Calculated manoeuvres: Update Operations

We all love a table with freshly calculated values, right? Here's how to update a table with calculated values. As they say, why calculate later when you can calculate now?

UPDATE TargetTable
SET Column1 = calculated_value
FROM (SELECT key, calculate_value(key) AS calculated_value FROM SourceTable) AS subquery
WHERE TargetTable.key = subquery.key;
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Be the function-master

For more complex operations on row-by-row level, let functions come to your rescue. Create a plpgsql function, with a LOOP for your own edge:

CREATE OR REPLACE FUNCTION process_data() RETURNS VOID AS $$
DECLARE
    temprow RECORD;
BEGIN
    FOR temprow IN SELECT * FROM TableName WHERE YourConditions LOOP
        -- All your fancy processing happens here... using temprow.column_name
    END LOOP;
    -- Remember to wave goodbye to your loop. We are not monsters, are we? 🙋‍♂️
END;
$$ LANGUAGE plpgsql;
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Sprucing up your iteration

Efficiency matters when dealing with a large number of records. Use your SQL wizardry to enhance the performance:

• Prune your results using WHERE clauses to reduce the dataset size.
• Don't be greedy! Only select columns that are necessary for your operations.
• Master the power of INDEXES. Their speedier lookups can save you loads of time!

Catch 'em all: Proper error handling

Remember Ash Ketchum from Pokemon? He never missed a Pokemon and you should never miss an error either. Build error resilience into your SQL functions for a stable and robust architecture:

BEGIN
    -- If it were a movie, this would be called -- 'The Try Block Begins'!
    -- [Your complex operations go here...]

EXCEPTION WHEN OTHERS THEN
    -- Erm...Pokemon, I mean, errors, I choose you!
    RAISE NOTICE 'Bummer! An error occurred: %', SQLERRM;
END;
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Eliminate the pesky bugs

Every coder's got some pesky bugs bugging them. Here are some tips to squash them:

• Don't use reserved keywords or system table names like 'temprow' to avoid collision.
• When using the INSERT INTO...SELECT statement, ensure the columns match like a perfect puzzle.
• Be mindful of those sneaky redundant semicolons in your PL/pgSQL code!

Masterclass - Advanced techniques

Playing around with 'sets'

Set over rows, anytime! Advanced SQL features like WINDOW functions, ranking, or running totals offer a set-based approach, often enhancing efficiency.

The rocking 'DO $$'

For standalone operations, the DO $$ block is your pal. All hail ad-hoc commands!

DO $$
BEGIN
   -- Your DJ set can start here!
END $$;
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Be 'current', always!

Ensure that your SQL wizardry is according to your actual database's version and specifications. As Dumbledore said, 'Help will always be given to those who ask for it'. 🧙‍♂️