In SQLite, we can use the TIME() function to subtract one or more seconds from a time value.
For datetime values, we can use the DATETIME() function.
Tag: how to
How to Get the Length of a String in Redis
In Redis, we can use the STRLEN command to get the length of a given string value, based on its key.
We can also use the HSTRLEN command to get the string length of a value stored in a hash.
4 Ways to Set a Key and its Expiry in Redis
Redis provides us with quite a few options for setting keys and any timeouts associated with those keys. Sometimes we can do it with a single command, other times we need two commands.
Here are four ways to set a key and its expiry in Redis.
Continue readingHow to Delete Duplicate Rows that have a Primary Key in SQL
The following examples use SQL to delete duplicate rows that have a primary key or unique identifier column.
Specifically, the examples delete all duplicates except one. So for example, in the case of three identical rows, it deletes two of them and keeps one.
Continue readingHow to Append a Value to a String in Redis
If we need to append a value to a string in Redis, we can use the APPEND command to do just that. All we need to do is call the command with the key name and the value to append.
2 Ways to Check if a Table has a Generated Column in PostgreSQL
PostgreSQL has supported generated columns since version 12. Generated columns can be created easily with the CREATE TABLE and ALTER TABLE statements.
We can check whether a table contains a generated column or not with the following methods.
Continue readingSet an Expiry on an Existing Key in Redis, But Only When the Key Already Has an Expiry
When setting a timeout for a key in Redis, we have the option of setting it only if the key already has an expiry. So, if the key doesn’t already have an associated timeout, the new timeout won’t apply. The new timeout will only apply if the key already has an existing timeout. In such cases the expiry will be reset to the new expiry.
We can do this with the XX option of the EXPIRE command. We can also use the XX option on commands such as EXPIREAT, PEXPIRE, and PEXPIREAT.
Fix “cannot add a STORED column” in SQLite
If you’re trying to add a generated column in SQLite, and you’re getting the “cannot add a STORED column” error, it’s probably because you’re trying to add a stored column.
In SQLite, we can only add virtual columns to existing tables.
Continue readingHow to Return Multiple Keys at Once in Redis
In Redis, the GET command is typically used to return the value of a single key that holds a string. But what if we need the values from multiple keys?
We can use the MGET command.
4 Ways to Increment a Key in Redis
In Redis, we have several options for incrementing a key. For example, if we set a key to 1, we can increment it by 1 to make 2. Or we can increment it by whatever amount we desire.
Below are four ways to increment a key in Redis.
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