What is the most efficient way to modify XML values To allow for precise modification of XML nodes and values, the XQuery XML query language employs an extension. SQL INNER JOIN Joining Two or More Tables. Summary in this tutorial, you will learn how to query data from multiple tables using SQL INNER JOIN statement. In the previous tutorial, you learned how to query data from a single table using the SELECT statement. Test Scenario for SQL Server Table Variables vs. Temp Tables Performance Testing. To test the performance of these objects we are going to run statements for each of. However, you often want to query data from multiple tables to have a complete result set for analysis. To query data from multiple tables you use join statements. SQL provides several types of joins such as inner join, outer joins left outer join or left join, right outer join or right join, and full outer join and self join. In this tutorial, we will show you how to use the INNER JOIN clause. SQL INNER JOIN syntax. The following illustrates INNER JOIN syntax for joining two tables INNERJOINtable2. ONjoincondition Lets examine the syntax above in greater detail The table1 and table2 are called joined tables. For each row in the table1, the query find the corresponding row in the table2 that meet the join condition. If the corresponding row found, the query returns a row that contains data from both tables. Otherwise, it examines next row in the table1, and this process continues until all the rows in the table1 are examined. For joining more than two tables, the same logic applied. SQL INNER JOIN examples. SQL INNER JOIN querying data from two tables example. In this example, we will use the products and categories tables in the sample database. The following picture illustrates the database diagram. In the diagram above One category can have many products. One product belongs to one and only one category. Therefore, there is a many to one relationship between the rows in the categories table and rows in the products table. The link between the two tables is the categoryid column. We need to query the following data from both tables product. ID, product. Name from the products table. Name from the categories table. The following query retrieves data from both tables product. ID,product. Name,category. Name categories. ONcategories. category. IDproducts. category. ID The join condition is specified in the INNER JOIN clause after the ON keyword as the expression categories. IDproducts. category. ID For each row in the products table, the query finds a corresponding row in the categories table that has the same categoryid. If there is a match between two rows in both tables, it returns a row that contains columns specified in the SELECT clause i. This process continues until the last row of the products table is examined. SQL INNER JOIN querying data from three tables. We can use the same techniques for joining three tables. The following query selects product. ID, product. Name, category. Name and supplier from the products, categories and suppliers tables categories. ONcategories. category. IDproducts. category. ID suppliers. ONsuppliers. IDproducts. supplier. IDImplicit SQL INNER JOINThere is another form of the INNER JOIN called implicit inner join as shown below In this form, you specify all joined tables in the FROM clause and put join condition in WHERE clause of the SELECT statement. We can rewrite the query example above using the implicit INNER JOIN as follows product. ID,product. Name,category. Name products. IDcategories. category. ID Visualize INNER JOIN using Venn diagram. We can use the Venn diagram to illustrates how the INNER JOIN works. The SQL INNER JOIN returns all rows in table 1 left table that have corresponding rows in table 2 right table. In this tutorial, we have shown you how to use the SQL INNER JOIN clause to select data from two or more tables based on a specified join condition.
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