Database Management Systems
If you’re getting a PostgreSQL error that reads “function generate_subscripts(numeric, integer) does not exist“, it’s probably because your first argument is not an array. This specific error message implies that the first argument is a numeric value, but we’d get a similar error when passing an integer.
The first argument for this function must be an array.
To fix this error, be sure that your first argument to generate_subscripts() is an array.
In PostgreSQL, we can use the array_cat() function to concatenate two arrays.
We pass both arrays as arguments when we call the function.
Continue readingIf you’re getting a PostgreSQL error that reads “searching for elements in multidimensional arrays is not supported“, it’s probably because you’re trying to perform an operation against a multi dimensional array when that operation only supports one dimensional arrays.
To fix this issue, perform the operation against a one dimensional array instead. You may be able to do this by applying the unnest() function against the multi dimensional array.
PostgreSQL has a function called btrim() that we can use to trim both sides of a string. We can trim blank spaces or we can specify certain characters to trim.
It removes the longest string containing only characters from the ones we specify. If we don’t specify any characters, then it removes blank spaces from both sides.
We provide the string as the first argument, and the (optional) characters as the second.
Continue readingIn PostgreSQL, we have many ways to retrieve data from arrays. One way is to specifically reference its subscript or a range of subscripts. Another way is to search through the array’s contents for the value we want.
By doing a search, I mean we could do things like filter the query with a WHERE clause, so that we only return rows that contain an array that has an element with a certain value.
In PostgreSQL, the array_prepend() function prepends an element to the start of an array.
The first argument is the element to prepend, and the second argument is the array.
Continue readingIn PostgreSQL, we can use the array_append() function to append an element to the end of an array.
The first argument is the array, and the second argument is the element to append.
Continue readingIf you’re getting an error that reads “could not determine polymorphic type because input has type unknown” when using the array_shuffle() function in PostgreSQL, it’s probably because your argument is of the wrong type.
The array_shuffle() function requires an array as its argument. Passing a non-array value will result in an error. The actual error can vary, depending on the argument you pass, but either way, 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 the array_shuffle() function.
PostgreSQL has an array_positions() function that returns the position of the all occurrences of a given value in an array.
There’s also a array_position() function (singular) that returns the position of just the first occurrence. So to get just the first occurrence, use that function instead.
If you’re getting an error that reads “multidimensional arrays must have array expressions with matching dimensions” it’s probably because you’re trying to create a multi-dimensional array where the inner arrays at the same level have different dimensions.
Multidimensional arrays must be rectangular. To fix this issue, make sure all arrays at the same level have the same dimensions.
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