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().
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 readingIf 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.
Continue readingWhen we create a scheduled event in MySQL, it’s enabled by default. But we can change this.
We can create an event in disabled status, then enable it later. Or we can do the opposite – create it as an enabled event and then disable it later.
Continue readingIf you’re getting a PostgreSQL error that reads “function generate_subscripts(integer, 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 an integer, but we’d get a similar error when passing a numeric argument.
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.
If you’re getting an error that reads “invalid input syntax for type integer…” when using the array_sample() function in PostgreSQL, it’s probably because your second argument is not an integer.
The second argument for this function must be an integer.
To fix this error, be sure that your second argument to array_sample() is an integer.
When we use psql to write SQL queries in PostgreSQL, we’ll usually see the results presented as a table, with columns displayed vertically and rows running horizontally. But it is possible to change this so that the columns are displayed horizontally and the rows run vertically.
This can be useful for when the number of columns causes the results to be wider than our psql display, and may cause the rows to wrap to the next line.
Here are five ways we can change the display to vertical output, otherwise known as expanded display.
Continue readingIn MySQL, GIPKs are invisible by definition. GIPK stands for generated invisible primary key, and it’s basically an invisible column automatically created by MySQL with a primary key constraint.
However, just because GIPKs are automatically created invisible, it doesn’t mean that we can’t “unhide” them – or make them visible.
We can make a GIPK visible just as we would make any other invisible column visible – use the ALTER TABLE statement to set it to VISIBLE.
PostgreSQL has a datestyle setting that specifies the display format for date and time values, as well as the rules for interpreting ambiguous date input values.Â
We can check the current value of our datestyle setting by running SHOW datestyle.