#8 PostgreSQL - ARRAY, sort the elements, how to use UNNEST,
Arrays in PostgreSQL are a collection of elements of the same data type. You can create arrays of any data type that is supported by PostgreSQL, including text, integer, boolean, and even arrays themselves.
Here are explanations of each of the SQL statements you provided:
SELECT ARRAY(SELECT unnest(Array[4,1,5,3]) ORDER BY 1) a
This statement creates an array of integers with the values 4, 1, 5, and 3, and then uses unnest to transform the array into a set of rows. The ORDER BY 1 sorts the rows in ascending order of the value in the first column. Finally, the ARRAY function is used to transform the set of rows back into an array. The resulting array will be {1,3,4,5}.
SELECT colors, array(SELECT unnest(colors) order by 1) FROM countries WHERE country_code LIKE '%U%';
This statement retrieves the colors array column from the countries table for rows where the country_code contains the letter 'U'. The unnest function is used to transform the colors array into a set of rows, and ORDER BY 1 sorts the rows in ascending order by the value in the first column. Finally, the ARRAY function is used to transform the set of rows back into an array. The resulting output will be a list of countries and their corresponding colors, with the colors sorted in ascending order.
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