I'm pretty new to Python and am completely confused by .join() which I have read is the preferred method for concatenating strings. I tried: strid = repr(595) print array.array('c', random.sample(
The fact that when it says INNER JOIN, you can be sure of what it does and that it's supposed to be just that, whereas a plain JOIN will leave you, or someone else, wondering what the standard said about the implementation and was the INNER/OUTER/LEFT left out by accident or by purpose.
This JOIN combines LEFT OUTER JOIN and RIGHT OUTER JOIN. It returns rows from either table when the conditions are met and returns NULL value when there is no match. In other words, OUTER JOIN is based on the fact that: ONLY the matching entries in ONE OF the tables (RIGHT or LEFT) or BOTH of the tables (FULL) SHOULD be listed.
INNER JOIN gets all records that are common between both tables based on the supplied ON clause. LEFT JOIN gets all records from the LEFT linked and the related record from the right table ,but if you have selected some columns from the RIGHT table, if there is no related records, these columns will contain NULL.
If a filter enters in a JOIN condition functionally (i.e. it is an actual join condition, not just a filter), it must appear in the ON clause of that join. Worth noting: If you place it in the WHERE clause instead, the performances are the same if the join is INNER, otherwise it differs. As mentioned in the comments it does not really matter since anyway the outcome is different. Placing the ...
Figure 1 is useful and correct as the first of 4 colourings of intersecting circle Venn diagrams for: (INNER) JOIN vs LEFT, RIGHT & FULL (OUTER) JOIN but not vs CROSS JOIN. Intersection rows are in JOIN, left/right rows are extra (null-extended) rows in LEFT/RIGHT JOIN. It includes CROSS JOIN as a special case of (INNER) JOIN where there are no rows in the non-intersection.
Left Join and Left Outer Join are one and the same. The former is the shorthand for the latter. The same can be said about the Right Join and Right Outer Join relationship. The demonstration will illustrate the equality. Working examples of each query have been provided via SQL Fiddle. This tool will allow for hands on manipulation of the query. Given Left Join and Left Outer Join Results
1 Do you really want to be able to join the tables if a value is null? Can't you just exclude the possible null values in the join predicate? I find it hard to grok that rows in two tables can be related by a null value.
At one time, this was closed as a duplicate of What is the difference between left, right, outer and inner joins, but that question does not address the difference between inner joins and natural joins.
