Joins Galore

Kevin Feasel

2017-01-13

Syntax

Lukas Eder has a comprehensive guide to joining data using SQL:

Alternative syntaxes: NATURAL JOIN

An more extreme and much less useful form of "EQUI" JOIN is the NATURAL JOIN clause. The previous example could be further “improved” by replacing USING by NATURAL JOIN like this:

SELECT *
FROM actor
NATURAL JOIN film_actor
NATURAL JOIN film

Notice how we no longer need to specify any JOIN criteria, because a NATURAL JOIN will automatically take all the columns that share the same name from both tables that it joins and place them in a “hidden” USING clause. As we’ve seen before, as primary keys and foreign keys have the same column name, this appears quite useful.

There is a high likelihood that you will learn at least one new thing here; for example, check out lateral joins (which SQL Server practitioners know as something else).

Related Posts

Odd Behavior With Altering Columns

Solomon Rutzky points out a few things which you can unintentionally change when running an ALTER TABLE [tbl] ALTER COLUMN [col] command: If the column is NOT NULL, then not specifying NOT NULL will cause it to become NULLable. The documentation for ALTER TABLE even states: ANSI_NULL defaults are always on for ALTER COLUMN; if not specified, the column is nullable. Let’s see […]

Read More

LISTAGG In Snowflake DB

Koen Verbeeck continues investigating Snowflake capabilities: Since SQL Server 2017, you have the STRING_AGG function, which has almost the exact same syntax as its Snowflake counterpart. There are two minor differences:– Snowflake has an optional DISTINCT– SQL Server has a default ascending sorting. If you want another sorting, you can specify one in the WITHIN GROUP clause. […]

Read More

Categories

January 2017
MTWTFSS
« Dec Feb »
 1
2345678
9101112131415
16171819202122
23242526272829
3031