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 ...
Inner join is a join that combined tables based on matching tuples, whereas outer join is a join that combined table based on both matched and unmatched tuple. Inner join merges matched row from two table in where unmatched row are omitted, whereas outer join merges rows from two tables and unmatched rows fill with null value.
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.
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
You can join tables on specific columns, I think you got that far. With the AND in the inner join you can specify it even more. Join the tables on the columns, where A1.Column = 'TASK' and throw away the rest. You could just as easily move the AND to the WHERE -Clause.
