LEFT OUTER JOIN Sales.SalesOrderHeader soh ON c.CustomerID = soh.CustomerID LEFT OUTER JOIN EXAMPLE 1 - Return all customerIDs with orders and no orders Hence, it is LEFT JOIN because the left table is the dominant of the two tables within the join having non-null values. LEFT JOIN returns inner rows + Non-NULL values from the left table with the right table’s null counterparts. There are 3 types based on the OUTER JOIN outputs. We can also derive the outer joins types from these. Okay, let’s go back to the list of expected outputs above. You can also do the same with the other tables. Table1 is the left table, and Table5 is the right table. LEFT OUTER JOIN Table5 e on a.column2 = e.column1 LEFT OUTER JOIN Table4 d on c.column1 = d.column2 If we add a fourth table, Table3 becomes the left table, and Table4 is the right table.
What about joining Table2 and Table3? Table2 becomes the left table, and Table3 is the right table. This refers to joining 2 tables: Table1 and Table2. Table1 is still the left table, and Table2 is the right table. In this case, to know what’s left or right, remember that a join works on 2 tables. LEFT OUTER JOIN Table3 c on b.column2 = c.column1 LEFT OUTER JOIN Table2 b on a.column1 = b.column1įrom the example above, Table1 is the left table, and Table2 is the right table. We can answer this question with examples: SELECT *
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Notice that I used “can be” and “can also be.” It depends on your WHERE clause (or if you ever include a WHERE clause) if it returns both inner and/or outer rows.īut from a SELECT statement, how can you determine which is the left or right table? Good question! How to Know Which is Left or Right Table in a Join? OUTER JOINS CAN RETURN BOTH INNER AND OUTER ROWS
Outer – because the outer rows can also be returned. Inner – because the exact results of the INNER JOIN can be returned. With that list, we can say that OUTER JOIN returns inner and outer rows. Finally, it could be a combination of all things described above. Non-NULL values from the right table with the null counterparts from the left table. Non-NULL values from the left table with the null counterparts from the right table. That’s the expression right after the ON keyword, much like the INNER JOIN output. All records that match the join condition or predicate. Here’s a complete list of what you can expect: Understanding outer joins starts with the output. Going back to antonyms, isn’t that the opposite of INNER JOINs? Not entirely, as you will see in the next section. If you want to get the records that don’t match, your only option is OUTER JOIN. For INNER JOINs, records with nulls won’t match, and they will be discarded and won’t appear in the result set. When you join 2 tables, one of the values from either table can be null. It’s optional!īut before we dive in, let’s discuss nulls concerning outer joins. To top that, you don’t have to include the word outer in your syntax explicitly. However, if you consider the outer join this way, you’ll be confused. If you missed part 1, here’s the link.īy the looks of it, outer is the opposite of inner. And this is part 2 of your ultimate guide to SQL joins. ORDER BY TABLENAME, object_name(i.Outer join is at the center stage today. T.NAME, i.object_id, i.index_id, i.name, p., t.schema_id very useful when "someone" (argh) decided to use various schema names with the same table AS Servername, This will include servername, dbname, and schemaname T.NAME, i.object_id, i.index_id, i.name, p. Sys.allocation_units a ON p.partition_id = a.container_id Sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id Sys.indexes i ON t.OBJECT_ID = i.object_id (sum(a.data_pages) * 8) / 1024 as DataSpaceMB (sum(a.used_pages) * 8) / 1024 as UsedSpaceMB, (sum(a.total_pages) * 8) / 1024 as TotalSpaceMB, So I thought I might post it here since this came up when searching for the original SQL I'd just like to start off by saying that I'm not the original author of this but I've used it over and over again.
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