luke | Please use the luke bundled

If you want to use the | async pipe it will only work on an Observable.

In your case this.objName is not an observable. this.objName is a value from property Firstname on object j which was emitted. You are trying to treat a single value as an observable - that's not how this works. Follow my example for better understanding on this.

Also try to use camelCase instead of PascalCase when naming properties (e.g FirstName to firstName).

You may use UNIQUE() function like-

To connect to an external MongoDB, simply adjust the Windows Shell call to point to external address. Per MongoDB docs, mongo by itself defaults to localhost at port 27017. For a remote host, adjust these defaults.

Using connection string:

You can overwrite default bootstrap class and make an exception for this scenario.

Basically you can change the order of a and b sort params depending on the order param you pass to your custom function. Then also based on the type of current param (string or number) you use different types of sort method.

Without prior knowledge about how MySQL works internally, there is no reason to assume that an index on just ts can be used to order by ts, primary_1 without doing an additonal (file)sort on primary_1. Imagine e.g. the edge case that all values for ts are the same - the index will just give you all rows, which you then have to sort by primary_1.

Nevertheless, MySQL can make use of some additional information: InnoDB stores secondary indexes in a way that includes the primary key columns (to be able to find the actual row in the table). Since that information is there anyway, MySQL can just make use of it - and it does, by using Index Extensions. This basically extends the index ts to an index ts, primary_1, primary_2.

So this technical trick allows you to use the index on ts to order by ts, primary_1, primary_2. But since there is always a "but", here is the "but":

Use of index extensions by the optimizer is subject to the usual limits on the number of key parts in an index (16) and the maximum key length (3072 bytes).

The index on ts, primary_1, primary_2 would be longer than 3072 bytes. You can e.g. also not create such an index manually. So this extension doesn't work anymore, and MySQL falls back to treating the index on ts like an index on just ts.

So why does it work for order by ts, primary_1? Well, even if, for those technical reasons, MySQL cannot create an internal index on ts, primary_1, primary_2, it could at least do it for ts, primary_1 without running into technical problems. MySQL actually doesn't do that though - but the MariaDB developers implemented this trick, so I assume you are actually using MariaDB. Nevertheless, the length restriction of 3072 still applies, so your order by both primary columns still won't work.

What can you do?

If you can shorten your primary keys a bit, the index extension would work again. Primary keys that long (and of that type) are uncommon and unpractical anyway (not only for this use case), so maybe you can find a different primary key for your table.

If that is not an option, you may be able to utilize some prior knowledge about your data distribution, e.g. if you know that at most 10 values for ts can be the same, you can first pick the first n+10 rows (using the index), then order only those by the primary keys. If you usually only show the first few pages, this might speed up your specific situation. But you may want to ask a separate question for it with specific details.

Just book+" "+chapter+":"+verse should do it. It's elementary string concatenation.

From what I understand you want to check if the keyword is matching name, dob, or gender. You need to modify your filter function like this, you just need to check if the keyword is matching any of the three desired properties.

Split columns and .drop_duplicates on data frame to remove duplicates and then append it back: