MySQL Shell: Built-In Help

It can be hard to recall all the details of how a program and API work. The usual way to handle that is to look at the manual or a book. Another – and in my opinion – nice way is to have built-in help, so you can find the information without changing between the program and browser. This blog discuss how to obtain help when you use MySQL Shell.

MySQL Shell is a client that allows you to execute queries and manage MySQL through SQL commands and JavaScript and Python code. It is a second generation command-line client with additional WebOps support. If you have not installed MySQL Shell yet, then you can download it from MySQL’s community downloads, Patches & Updates in My Oracle Support (MOS) (for customers), or Oracle Software Delivery Cloud (for trial downloads). You can also install it through MySQL Installer for Microsoft Windows.
MySQL Shell: Get help for a table object
MySQL Shell: Get help for a table object

MySQL Shell has a very nice and comprehensive built-in help. There is of course the help output produced using the --help option if you invoke the shell from the command line:

However, this help is not what makes MySQL Shell special. It is the help that you can see from within the shell when working in JavaScript or Python that is the worth some extra attention. There is both support for general help and obtaining help through objects.

General Help

The first layer of help is what is also known from the old mysql command-line client. A command existing of a backslash and a ?, h, or help (\?, \h or \help) will show information about the general usage of MySQL Shell:

This shows which commands and global objects are available. But there is more: you can also get help about the usage of MySQL Shell such as how to use the Admin API (for MySQL InnoDB Cluster), how to connect, or the SQL syntax. The search for relevant help topics are context sensitive, for example searching for the word select return different results depending on the mode and whether you are connected:

  • In Python or JavaScript mode without a connection, it is noted that information was found in the mysqlx.Table.select and mysqlx.TableSelect.select categories.
  • In Python or JavaScript mode with a connection, the SELECT SQL statement is included as a category.
  • In SQL mode the actual help text for the SELECT SQL statement is returned (requires a connection).

For example, to get help about the select method of a table object:

To get help for the SELECT SQL statement:

Note here how it is possible to get the help for the SELECT statement both from the Python (and JavaScript) as well as SQL modes, but the search term is different.

Tip: To get information about SQL statements, you must be connected to a MySQL instance.

When you use the JavaScript or Python modes there is another way to get  help based on your object. Let’s look at that.

Object Based Help

If you are coding in MySQL Shell using JavaScript or Python it may happen you need a hint how to use a given object, for example a table object. You can use the method described in the previous section to get help by searching for mysqlx.Table, however, you can also access the help directly from the object.

All of the X DevAPI objects in MySQL Shell has a help() method that you can invoke to have help returned for the object. For example, if you have an object named city for the city table in the world schema, then calling city.help() returns information about table object:

As you can see, the built-in help in MySQL Shell is a powerful resource. Make sure you use it.

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