Database.Guide – Page 160

Redis SUBSTR Equivalent

July 26, 2022 by Ian

Many SQL databases have a SUBSTR() or equivalent function that returns a substring from a specified string.

Redis has a SUBSTR command, but it was deprecated in Redis 2.0.0.

However, Redis also has the GETRANGE command, that basically does the same thing. Basically, anything that was possible with the Redis SUBSTR command, is now possible with the GETRANGE command.

And the GETRANGE command does basically the same thing that most of the SUBSTR() and SUBSTRING() functions do in the SQL world – gets a substring from a string.

4 Ways to Return a Key’s Expiry in Redis

July 25, 2022 by Ian

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.

Return Rows that Contain Only Non-Alphanumeric Characters in SQL

July 24, 2022 by Ian

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.

Redis OBJECT ENCODING Command Explained

July 23, 2022 by Ian

In Redis, the OBJECT ENCODING command returns the internal encoding for the Redis object stored at the specified key.

How to Increment a Floating Point Number in Redis

July 22, 2022 by Ian

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.

Redis RANDOMKEY Command Explained

July 21, 2022 by Ian

In Redis, the RANDOMKEY command returns a random key from the currently selected database.

How to Set Multiple Strings in Redis

July 20, 2022 by Ian

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.

2 Ways to List All Tables in a PostgreSQL Database

July 19, 2022 by Ian

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.

Redis KEYS Command Explained

July 18, 2022 by Ian

In Redis, the KEYS command returns all keys in the database matching a given pattern.

Redis DUMP Command Explained

July 17, 2022 by Ian

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.