Hello-
I am confused with inner and outer joins. Can someone explain to me exactly what the differences are? The reason I am asking is I am trying to populate a datagrid from multiple tables. The SQL query currently pulls out all customers that have revenue only, When in fact I need it to pull out all customers regardless of revenue so that I can see which customers have "0" revenue.
Here is my sql query which sorts each day into a new datagrid column.
SQL = "SELECT revenue_forecast.oct_03 AS 'forecast', pb_customers.customer_name AS 'customer', sum(case when day(pb_report_shippers.shipper_date_time) = 1 then pb_report_shippers.total_ext_price + pb_report_shippers.setup_cost else 0 end) as day1, sum(case when day(pb_report_shippers.shipper_date_time) = 2 then pb_report_shippers.total_ext_price + pb_report_shippers.setup_cost else 0 end) as day2, FROM pb_report_shippers Left outer JOIN pb_jobs ON pb_report_shippers.job_id = pb_jobs.job_id left outer JOIN pb_customers ON pb_jobs.customer_id = pb_customers.customer_id left outer JOIN revenue_forecast ON pb_customers.customer_id = revenue_forecast.customer_id WHERE pb_report_shippers.shipper_date_time between cast('11/01/03' as datetime) and cast('11/2/03' as datetime) AND pb_report_shippers.job_completed IN('1','0') AND pb_customers.customer_deleted <> '1' GROUP by pb_customers.customer_name, revenue_forecast.oct_03 Order BY pb_customers.customer_name"
Any help would be appreciated. ThanksFrom the BOL:
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Joins can be categorized as:
Inner joins (the typical join operation, which uses some comparison operator like = or <>). These include equi-joins and natural joins.
Inner joins use a comparison operator to match rows from two tables based on the values in common columns from each table. For example, retrieving all rows where the student identification number is the same in both the students and courses tables.
Outer joins. Outer joins can be a left, a right, or full outer join.
Outer joins are specified with one of the following sets of keywords when they are specified in the FROM clause:
LEFT JOIN or LEFT OUTER JOIN
The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.
RIGHT JOIN or RIGHT OUTER JOIN.
A right outer join is the reverse of a left outer join. All rows from the right table are returned. Null values are returned for the left table any time a right table row has no matching row in the left table.
FULL JOIN or FULL OUTER JOIN.
A full outer join returns all rows in both the left and right tables. Any time a row has no match in the other table, the select list columns from the other table contain null values. When there is a match between the tables, the entire result set row contains data values from the base tables.
Cross joins.
Cross joins return all rows from the left table, each row from the left table is combined with all rows from the right table. Cross joins are also called Cartesian products.
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So I would put the customers table first, then outer join the other tables.
SQL = "SELECT .... FROM pb_customers left outer join ..."
|||Eric-
Thanks for the explanation.
I tried placing the pb_customers table first as you suggested, but I still get a list of customers who have revenue.
Here is the from part of the SQL Query
FROM pb_customers left Outer Join revenue_forecast ON pb_customers.customer_id = revenue_forecast.customer_id Left Outer Join pb_jobs ON pb_jobs.customer_id = pb_customers.customer_id Left Outer Join pb_report_shippers ON pb_report_shippers.job_id = pb_jobs.job_id WHERE pb_report_shippers.shipper_date_time between cast('11/01/03' as datetime) and cast('11/4/03' as datetime) AND pb_report_shippers.job_completed IN('1','0') AND pb_customers.customer_deleted <> '1' GROUP by pb_customers.customer_name, revenue_forecast.oct_03 Order BY pb_customers.customer_name "
Any ideas?|||Make sure you get the outer join working by taking it in small steps. Just create a query with your first left outer join, make sure it returns what you want, continue adding tables. So start with pb_customers and revenue_forecast. Then add pb_report_shippers and so forth. Tell us what happens there.
