Database Management Systems
There are several ways to return a key’s expiry in Redis. The method used depends on how we want the expiry to be returned.
We can use the TTL command to return the timeout in seconds. We can alternatively use the PTTL command to return it in milliseconds. Another way to do it is to use the EXPIRETIME which returns the absolute Unix timestamp of the key in seconds, or the PEXPIRETIME command which returns the absolute Unix timestamp of the key in milliseconds.
Here are examples of using SQL to return rows that contain non-alphanumeric characters in various DBMSs.
Non-alphanumeric characters include punctuation characters like !@#&()–[{}]:;',?/* and symbols like `~$^+=<>“, as well as whitespace characters like the space or tab characters.
In Redis, the OBJECT ENCODING command returns the internal encoding for the Redis object stored at the specified key.
The INCR command is commonly used in Redis to increment a value by one. And the INCRBY command can be used to increment a valued by a specified integer. But neither of those commands let us work with floating point numbers.
If we want to use floating point numbers, we can use the INCRBYFLOAT command.
In Redis, the RANDOMKEY command returns a random key from the currently selected database.
Redis provides us with a convenient way to set multiple strings at once. Specifically, the MSET command enables us to set multiple strings in one go.
There’s also the MSETNX command which does the same thing, but only if none of the keys already exist.
Here are a couple of options for getting a list of tables in a database in PostgreSQL.
The first option is a psql command, the second involves querying an information schema view.
In Redis, the KEYS command returns all keys in the database matching a given pattern.
The Redis DUMP command serialises the value stored at a specified key in a Redis-specific format and returns it to the user.
The serialisation format contains a 64-bit checksum that is used to make sure errors will be detected. The values are in the same format used by the RDB. Also, an RDB version is encoded inside the serialised value, so that different Redis versions with incompatible RDB formats will refuse to process the serialised value.
Continue readingThe Redis TOUCH command alters the last access time of a key or keys. It allows us to alter the access time of a key without accessing it directly.