Below are examples of using SQL to return the first day of the month across various DBMSs.
This could be the first day of the current month, or the first day of a month based on a given date.
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6 Ways to Set a String in Redis
When working with Redis, we have a number of options for setting keys that store string values.
Here are six ways to set a string value in Redis.
2 Ways to Remove a Key’s Expiry in Redis
A Redis key can have an optional timeout, which makes the key expire after a certain amount of time, or at a certain time. We can use a couple of methods to remove any timeout associated with a key.
Here are two ways to remove a key’s expiry in Redis.
How to Update a Key and Return its Old Value in a Single Operation in Redis
When using the SET command to set a key in Redis, we can use the GET option to return its old value. This allows us to update the value of a key while returning the value that we’re replacing it with.
Note that this option was introduced in Redis 7.0.0, so if it doesn’t work, check your Redis version. If using an earlier version, try the GETSET command instead (which is deprecated from Redis version 6.2.0).
Subtract Months from a Date in SQLite
In SQLite, we can use the DATE() function to subtract one or more months from a date.
For datetime values, we can use the DATETIME() function.
4 Ways to Decrement a Key in Redis
In Redis, we have several options for decrementing a key. By this, I mean, reducing the value of a key by one or more. For example, if we set a key to 15, we can decrement it by 1 to make 14. Or we can increment it by whatever amount we desire.
Get the First, Second, Third, or Fourth Monday of a Year in SQLite
We can use SQLite’s DATE() function to return the first, second, third, fourth, etc instance of a given day within a given year.
We can use the same technique to return the first Monday of each month in the year.
It’s not limited to Monday though. The same techniques can be used on Tuesday, Wednesday, Thursday, Friday, etc.
Set an Expiry on an Existing Redis Key Only When the Key Doesn’t Already Have an Expiry
When setting an expiry for an existing key in Redis, we now have the option to set the expiry only if the key doesn’t already have an expiry. That’s because Redis 7.0.0 introduced some new options that allows us to do this and other things.
In this case, we can use the NX option when setting the expiry to specify that the expiry should only be set if the key doesn’t already have an expiry. We can use this option on commands such as EXPIRE, EXPIREAT, PEXPIRE, and PEXPIREAT.
Add Seconds to a Time Value in PostgreSQL
In PostgreSQL, we can use the + operator to add one or more seconds to a time value.
By “time” value, this could be an actual time value, a timestamp, or an interval. We can also add seconds to a date value or a date and time combination.
How to Create a Generated Column in MariaDB
A generated column is a database column whose value is an expression. Therefore, the value of the generated column is usually derived (for example, it could be derived from values in other columns).
Generated columns are also sometimes referred to as computed columns or virtual columns.
Creating a generated column in MariaDB is essentially the same as creating a normal column. The difference is that the definition of the generated column contains an expression that determines the column’s value.