In addition, this code uses two columns to order the data i.e. For records that exist Sales.SalesPerson table and not in the Sales.SalesTerritory table, NULL values are returned for the columns in the Sales.SalesTerritory. Rows between the Person.Contact and Sales.SalesPerson tables in conjunction with all of the data from the Sales.SalesPerson table and matching In the sample code below, we are retrieving the matching In the following query we are combining two concepts to show that more than two tables can be JOINed in one SELECT statement and more than one JOIN type can be used in a single SELECT statement. Finally, the result set is returned in order with the most expensive first based on the ORDER BY clause and only the highest 100 products based on the TOP clause.
The records are filtered by only returning records with the SOD.UnitPrice The JOINĬondition is based on matching rows in the SOD.ProductID and P.ProductID columns. The tables are aliased with the following: SOD for Sales.SalesOrderDetail and P for Production.Product. In the following query we have a SQL INNER JOIN clause between the Sales.SalesOrderDetail and Production.Product tables. SQL statements for each type of JOIN then provide some insight into the usage and sample result sets. Let's walk through examples from the AdventureWorks sample database that is available for SQL Server to provide example
#Adventureworks database tables full
SQL FULL JOIN - Based on the two tables specified in the join clause, all data is returned from both tables regardless of matching data.Please heed caution when using a CROSS JOIN. The size of the Cartesian product is based on multiplying the number of rows from the left table by the number of rows in the right table. SQL CROSS JOIN - Based on the two tables specified in the join clause, a Cartesian product is created if a WHERE clause does filter the rows.SQL Self Join - In this circumstance, the same table is specified twice with two different aliases in order to match the data within the same table.On the left table, the matching data is returned in addition to NULL values where a record exists in the right table but not in the left table. SQL RIGHT OUTER JOIN - Based on the two tables specified in the join clause, all data is returned from the right table.So you can change either the order of the tables in the specific join statement or change the JOIN from left to right or vice versa and get the same results. Another item to keep in mind is that the LEFT and RIGHT OUTER JOIN logic is opposite of one another.On the right table, the matching data is returned in addition to NULL values where a record exists in the left table, but not in the right table. SQL LEFT OUTER JOIN - Based on the two tables specified in the join clause, all data is returned from the left table.Although most join logic is based on matching values between the two columns specified, it is possible to also include logic using greater than, less than, not equals, etc.As such, please take the time to understand the data being requested then select the proper join option. Although that is the case in some environments, it is really dependent on the database design, referential integrity and data needed for the application. Just to add a little commentary to the basic definitions above, in general the INNER JOIN option is considered to be the most common join needed in applications and/or queries.Preferably the join is based on referential integrity enforcing the relationship between the tables to ensure data integrity. SQL INNER JOIN - Match rows between the two tables specified in the INNER JOIN statement based on one or more columns having matching data.syntax, but the support has been reduced and the best practice in SQL Server is to use the syntax outlined in the examples below.īefore we jump into code, let's provide some baseline information on the In previous versions of SQL Server, join logic could also have been included in the WHERE clause with = (INNER JOIN), *= (LEFT OUTER JOIN), =* (RIGHT OUTER JOIN), etc. In a nutshell, joins are typically performed in the FROM clause of a table or view for the SELECT, INSERT.SELECT, SELECT.INTO,ĭELETE statements. Joining tables to obtain the needed data for a query, script or stored procedure is a key concept as you learn about SQL Server development.