UNNEST

1
SELECT UNNEST(ARRAY[a, b, c]);

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SELECT idx, element
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FROM UNNEST(ARRAY[first, second, third]) 
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  WITH ORDINALITY AS t(element, idx);

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SELECT 
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  p.name,
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  t.tag
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FROM products p
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CROSS JOIN UNNEST(p.tags) AS t(tag)
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WHERE t.tag = featured;

1
SELECT * FROM UNNEST(
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  ARRAY[1, 2, 3],
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  ARRAY[a, b, c]
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) AS t(num, letter);