Database.Guide – Page 151

Fix “WRONGTYPE Operation against a key holding the wrong kind of value” When Calling SUNION or SUNIONSTORE in Redis

October 23, 2022 by Ian

If you’re getting an error that reads “WRONGTYPE Operation against a key holding the wrong kind of value” when calling either the SUNION command or the SUNIONSTORE command in Redis, it’s probably because you’re passing a key with the wrong data type.

To fix this issue, make sure that each key that you pass holds a set.

3 Ways to Return all Members of a Set in Redis

October 22, 2022 by Ian

When working with Redis, we have multiple ways to return the members of a set. Here are 3 ways to return the members of a set in Redis.

How to Get a Key’s Type in Redis

October 21, 2022 by Ian

If you know the name of a key in Redis, but you want to find out it’s type (eg, string, list, hash, set, etc), look no further than the TYPE command. This command returns the string representation of the type of the value at the given key.

How to Return a Random Key in Redis

October 20, 2022 by Ian

If you ever find yourself in the situation where you need to get a random key when using Redis, take a look at the RANDOMKEY command.

This command returns a random key from the currently selected database.

2 Ways to Sort the Elements in a Redis List, Set, or Sorted Set

October 19, 2022 by Ian

Redis provides a couple of commands that allow us to sort the elements in a list, set, or sorted set.

The SORT command is probably the most obvious, and does exactly what its namesake promises. However, there’s also a SORT_RO command, which is a read-only variant of the SORT command.

Add Minutes to a Time Value in PostgreSQL

October 18, 2022 by Ian

In PostgreSQL, we can use the + operator to add one or more minutes to a time value.

By “time” value, this could be an actual time value, a timestamp, or an interval. We can also add minutes to a date value or a date and time combination.

2 Ways to Rename a Key in Redis

October 17, 2022 by Ian

There are a couple of commands that enable us to rename a key in Redis. The one we use will depend on whether or not we want to overwrite any existing keys.

Fix: “ERR syntax error” when using SPOP in Redis

October 16, 2022 by Ian

If you’re getting an error that reads “ERR syntax error” in Redis, it could be because you’re calling the SPOP command with too many arguments.

At the time of writing, I find that I only get this argument when I pass too many arguments. If I pass no arguments, I get a different error.

How to Get a Substring in Redis

October 15, 2022 by Ian

If we have a key that holds a string value, we can use the GETRANGE command to get a substring from that value.

Redis also has a SUBSTR command that does the same thing, but that was deprecated in Redis 2.0.0, in favour of the GETRANGE command.

How to Copy a Key’s Value to Another Key in Redis

October 14, 2022 by Ian

As from Redis 6.2.0, we can use the COPY command whenever we need to copy a key’s value to another key.