A Brief Overview of SUBSTR() in PostgreSQL

Posted on by Ian

In PostgreSQL, we can use the the substr() function to return a substring from a string, based on a starting point. We have the option of specifying how many characters to return.

We pass the string as the first argument and the start position as the second. If we want to specify how long the substring should be, we can pass a third argument that specifies how many characters to return.

The function returns the same result as the substring() function (which uses a slightly different syntax).

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Fix “function array_sample(numeric, integer) does not exist” in PostgreSQL

Posted on by Ian

If you’re getting an error that reads “function array_sample(numeric, integer) does not exist” when using the array_sample() function in PostgreSQL, it’s probably because your first argument is a numeric type instead of an array.

The first argument for this function must be an array.

To fix this error, be sure that your first argument to array_sample() is an array, not a numeric value.

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How to Create a MySQL Event Only if it Doesn’t Already Exist

Posted on by Ian

In MySQL we can use the CREATE EVENT statement to create scheduled events. As with many CREATE ... statements, we have the option of using the IF NOT EXISTS clause to specify that the object should only be created if it doesn’t already exist.

Of course, we wouldn’t normally be trying to create an event if we know that it already exists. But there may be times where we’re not sure, and we want our code to handle this scenario without throwing an error if an event with the same name already exists. This is common when creating scripts that are designed to be run across multiple environments. That’s where the IF NOT EXISTS clause can come in handy.

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A Quick Look at PostgreSQL’s REGEXP_LIKE() Function

Posted on by Ian

In PostgreSQL, we can use the regexp_like() function to check whether or not a match of a POSIX regular expression occurs within a given string.

We pass the string as the first argument and the pattern as the second argument. We can also provide a flag as an optional third argument, which determines how the function behaves.

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Fix “function array_shuffle(integer) does not exist” in PostgreSQL

Posted on by Ian

If you’re getting an error that reads “function array_shuffle(integer) does not exist” when using the array_shuffle() function in PostgreSQL, it’s probably because the argument you’re passing to the function is not an array.

More specifically, this error message implies that you’re passing an integer. The same error can occur when passing other non-array types (such as numeric), but the solution is the same.

The argument for this function must be an array.

To fix this error, replace the integer value with an array value when calling the array_shuffle() function.

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Understanding PostgreSQL’s REGEXP_INSTR() Function

Posted on by Ian

In PostgreSQL, the regexp_instr() function returns the starting or ending position of the N‘th match of a POSIX regular expression pattern to a string. If there’s no match, it returns zero.

We pass the string and pattern as arguments. The function also accepts some optional arguments that allow us to be specific with how the function works.

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