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Fix Error “could not determine polymorphic type because input has type unknown” when using generate_subscripts() in PostgreSQL

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If you’re getting an error that reads “could not determine polymorphic type because input has type unknown” when using the generate_subscripts() function in PostgreSQL, it’s probably because your first argument is of the wrong type.

The generate_subscripts() function requires an array as its first argument. Passing a non-array value will result in an error. The actual error can vary, depending on the argument you pass, but regardless, the error is usually due to a non-array argument being passed.

To fix this error, be sure to pass an array as the argument when calling generate_subscripts().

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A Quick Look at the && Operator in PostgreSQL

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We can use the && operator in PostgreSQL to check two arrays for any overlapping elements.

We include an array on each side of the operator to compare them, and the result is a Boolean value that indicates whether or not there’s any overlap. A result of True (or t) indicates that there’s an overlap, while False (or f) indicates there’s no overlap.

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A Quick Overview of ARRAY_NDIMS() in PostgreSQL

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In PostgreSQL the array_ndims() function returns the number of dimensions of an array. We pass the array to the function, and it returns an integer of the number of dimensions in the array.

This function is not to be confused with the array_dims() function, which returns a more detailed text representation of the dimensions in the array.

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Fix “sample size must be between…” Error when using array_sample() in PostgreSQL

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If you’re getting an error that starts with “sample size must be between…” when using the array_sample() function in PostgreSQL, it’s probably because your second argument is either a negative value, or it’s larger than the number of elements in the array.

The second argument must be no less than zero, and it can’t be any larger than the number of elements in the array.

To fix this error, be sure that your second argument is greater than zero and less than or equal to the number of elements in the array at the first argument.

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Understanding ARRAY_DIMS() in PostgreSQL

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In PostgreSQL we can use the array_dims() function to return information about the dimensions in an array. The function accepts the array in question, and it returns a text representation of the array’s dimensions.

This function is not to be confused with the array_ndims() function, which simply returns the number of dimensions in an array.

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