Database Management Systems
In PostgreSQL, the @> operator checks to see whether the first array contains the second array. That is, whether or not the array on the left of the operator contains all elements in the array to the right.
The function returns a Boolean result: It returns true if the first array contains the second, and false if it doesn’t. If the result is unknown, it returns NULL.
In PostgreSQL, we can create arrays and select data from within them. We can select the whole array, an individual element, or a slice.
A slice is a portion of the array returned in its own array. For example, we could extract 3 elements from the middle of an array that has 9 elements.
Continue readingIf 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().
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.
PostgreSQL has an ALL() construct that we can use when searching for data inside arrays. It returns a Boolean result, which reflects whether the condition is true or not.
In PostgreSQL, we can use the ANY() construct to perform searches against arrays. It returns a Boolean result, and so we can incorporate this into our searches to return just those rows that yield true or false, as the case may be.
There’s also a SOME() construct, which is a synonym for ANY().
In MySQL, scheduled events are tasks that run according to a specified schedule. When we no longer require an event we can drop it so that it doesn’t take up unnecessary room in the system. We have a couple of ways of going about this.
Continue readingIn PostgreSQL, the array_upper() function returns the upper bound of the specified array dimension. We pass the array as well as the dimension, and it returns the upper bound accordingly.
In PostgreSQL, the array_lower() function returns the lower bound of the specified array dimension. We pass the array and the relevant dimension, and it returns the lower bound for that dimension.
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.