In this post, we revert to the discussion on Teradata:
We will cover help and show commands. Help is a command to list the database objects. For example, we have Help Database, help user, help table, help volatile table, help view, help macro, help procedure, help trigger, help column etc. These display information of the corresponding database objects. The different database objects are aggregate functions (A), combined/analytical functions(B), External stored procedure(E), Function (F), Trigger(G), Method(H), Join Index(I), Journal Table(J), Macro(M), Hash Index(N), Procedure (P), Queue Table (Q), Table Function (R), Ordered Analytical Function (S), Table (T), UDT(U), View(V) and Authorization(X)  There's also corresponding help available for index, statistics, constraint, session, SQL, SPL etc.
Comments can also be added to database objects. These are displayed on help.
Runtime information such as sessions are also displayed. The parsing engine assigns Session.
The show command is used to show the SQL used to create the corresponding database object. For example, the SHOW TABLE <table-name> can be used to create the table statement needed to create the table. Table, view, macro, trigger, procedure can all be shown.
 Aggregates such as count when used with a column specifier ignores null values. When used with a star to denote all columns, includes rows with null values.  The common aggregates are MIN, MAX, AVG, SUM and COUNT. GROUP BY delivers one row per group. Rows can be restricted when used with a predicate and this improves performance. The predicate clause also helps skip calculations in aggregation. The having clause acts as a filter on all aggregates.
 Grouping Sets, rollup and cube are three grouping options.
The Nexus tool could be used for all groupings.
 Joins can be INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN and FULL OUTER JOIN. A PRODUCT JOIN is a Cartesian product and often not intended.