PostgreSQL allows us to create sequence objects, otherwise known as “sequence generators”, or simply “sequences”. As the name suggests, a sequence object is used to generate sequence numbers.
We can use sequences to generate incrementing numbers or decrementing numbers.
Continue readingIf you’re getting error msg 9809 which reads something like The style … is not supported for conversions from … to … in SQL Server, it’s probably because you’re trying to convert between data types, but the style that you’re specifying isn’t supported for that operation.
It’s not that the conversion can’t happen, it’s just that the style that you’re providing is wrong.
Continue readingIn SQL Server, we can use functions like CONVERT() or FORMAT() to convert a valid date type into a format like yyyymmdd.
This format adheres to the ISO 8601 standard, which defines dates to be written as yyyymmdd, or when using delimiters, as yyyy-mm-dd.
In SQL Server, the date type expresses dates in the yyyy-mm-dd format, but we can use the following technique to remove the delimiters and express the date as yyyymmdd.
Continue readingIf you get an error that reads “WRONGTYPE Operation against a key holding the wrong kind of value” when using the ZPOPMIN or ZPOPMAX commands in Redis, it’s because you’re passing a key with the wrong data type.
The same issue can apply when using the blocking variants of these commands (BZPOPMIN and BZPOPMAX).
To fix this issue, make sure you pass a sorted set to these commands.
Continue readingWhen working with SQL Server, if we’re given a number that represents a date in the yyyymmdd format, we can use functions like CAST() or CONVERT() to convert that number to a valid date type. This will enable us to perform date operations against it that we might not be able to do when it’s still in numeric form.
Prior to PostgreSQL 10, if we wanted to create an auto-incrementing column, we would typically use the SERIAL type, or we’d create our own sequence and apply it to an integer column.
But from PostgreSQL 10 onwards, we’ve been able to create identity columns.
Continue readingIf you’re getting an error that reads something like “Cannot drop a default constraint by DROP DEFAULT statement. Use ALTER TABLE to drop a constraint default“, it’s because you’re trying to use DROP DEFAULT to drop a DEFAULT constraint.
The DROP DEFAULT statement has been flagged for deletion from SQL Server, and Microsoft recommends that we use the ALTER TABLE statement to drop DEFAULT constraints.
Therefore, to fix this issue, use the ALTER TABLE statement to drop the DEFAULT constraint.
If you’re getting an error that reads “ERR wrong number of arguments for ‘hstrlen’ command“, it’s because you’re passing the wrong number of arguments when using the HSTRLEN command.
The HSTRLEN command requires two arguments (at the time of writing). These are the name of the key and the name of the field.
If you’re getting this error, check the number of arguments that you’re passing and adjust if required.
Continue readingIf you’re getting an error in MySQL that reads something like “ERROR 1054 (42S22): Unknown column ‘c.DogName’ in ‘on clause”“, here are three likely causes:
When creating a sequence object in SQL Server, the default data type is bigint. However, we can change this so that the sequence uses a data type of our choosing, as long as it’s an integer type (see below for accepted data types).
We can set the data type of a sequence by using the AS argument when defining the sequence.