Joins indicate how Microsoft SQL Server should use data from one table to select. A simplified ISO FROM clause join syntax is. An inner, outer, or cross join. The non-ansi JOIN syntax for outer joins was deprecated in SQL Server 2005; you will need to use the ansi LEFT JOIN syntax. SQL Server, non-ANSI join operators.

1. Using Self-Joins
2. Left Outer Join Syntax Oracle

Description SQL Server (Transact-SQL) JOINS are used to retrieve data from multiple tables. A SQL Server JOIN is performed whenever two or more tables are joined in a SQL statement. There are 4 different types of SQL Server joins:.

SQL Server INNER JOIN (or sometimes called simple join). SQL Server LEFT OUTER JOIN (or sometimes called LEFT JOIN). SQL Server RIGHT OUTER JOIN (or sometimes called RIGHT JOIN). SQL Server FULL OUTER JOIN (or sometimes called FULL JOIN) So let's discuss SQL Server JOIN syntax, look at visual illustrations of SQL Server JOINS, and explore SQL Server JOIN examples.

INNER JOIN (simple join) Chances are, you've already written a statement that uses an SQL Server INNER JOIN. It is the most common type of join. SQL Server INNER JOINS return all rows from multiple tables where the join condition is met. Syntax The syntax for the INNER JOIN in SQL Server (Transact-SQL) is: SELECT columns FROM table1 INNER JOIN table2 ON table1.column = table2.column; Visual Illustration In this visual diagram, the SQL Server INNER JOIN returns the shaded area: The SQL Server INNER JOIN would return the records where table1 and table2 intersect.

Example Here is an example of an INNER JOIN in SQL Server (Transact-SQL): SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers INNER JOIN orders ON suppliers.supplierid = orders.supplierid; This SQL Server INNER JOIN example would return all rows from the suppliers and orders tables where there is a matching supplierid value in both the suppliers and orders tables. Let's look at some data to explain how the INNER JOINS work: We have a table called suppliers with two fields (supplierid and suppliername). It contains the following data: supplierid suppliername 10000 IBM 10001 Hewlett Packard 10002 Microsoft 10003 NVIDIA We have another table called orders with three fields (orderid, supplierid, and orderdate). It contains the following data: orderid supplierid orderdate 50 2003/26 /27 /05/14 If we run the SQL Server SELECT statement (that contains an INNER JOIN) below: SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers INNER JOIN orders ON suppliers.supplierid = orders.supplierid; Our result set would look like this: supplierid name orderdate 10000 IBM 2003/1 Hewlett Packard 2003/05/13 The rows for Microsoft and NVIDIA from the supplier table would be omitted, since the supplierid's 10002 and 10003 do not exist in both tables. The row for 500127 (orderid) from the orders table would be omitted, since the supplierid 10004 does not exist in the suppliers table. Old Syntax As a final note, it is worth mentioning that the SQL Server INNER JOIN example above could be rewritten using the older implicit syntax as follows (but we still recommend using the INNER JOIN keyword syntax): SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers, orders WHERE suppliers.supplierid = orders.supplierid.

LEFT OUTER JOIN Another type of join is called a SQL Server LEFT OUTER JOIN. This type of join returns all rows from the LEFT-hand table specified in the ON condition and only those rows from the other table where the joined fields are equal (join condition is met). Syntax The syntax for the LEFT OUTER JOIN in SQL Server (Transact-SQL) is: SELECT columns FROM table1 LEFT OUTER JOIN table2 ON table1.column = table2.column; In some databases, the LEFT OUTER JOIN keywords are replaced with LEFT JOIN.

Visual Illustration In this visual diagram, the SQL Server LEFT OUTER JOIN returns the shaded area: The SQL Server LEFT OUTER JOIN would return the all records from table1 and only those records from table2 that intersect with table1. Example Here is an example of a LEFT OUTER JOIN in SQL Server (Transact-SQL): SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers LEFT OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; This LEFT OUTER JOIN example would return all rows from the suppliers table and only those rows from the orders table where the joined fields are equal. If a supplierid value in the suppliers table does not exist in the orders table, all fields in the orders table will display as in the result set.

Let's look at some data to explain how LEFT OUTER JOINS work: We have a table called suppliers with two fields (supplierid and suppliername). It contains the following data: supplierid suppliername 10000 IBM 10001 Hewlett Packard 10002 Microsoft 10003 NVIDIA We have a second table called orders with three fields (orderid, supplierid, and orderdate).

It contains the following data: orderid supplierid orderdate 50 2003/26 /05/13 If we run the SELECT statement (that contains a LEFT OUTER JOIN) below: SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers LEFT OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; Our result set would look like this: supplierid suppliername orderdate 10000 IBM 2003/1 Hewlett Packard 2003/2 Microsoft 10003 NVIDIA The rows for Microsoft and NVIDIA would be included because a LEFT OUTER JOIN was used. However, you will notice that the orderdate field for those records contains a value.

RIGHT OUTER JOIN Another type of join is called a SQL Server RIGHT OUTER JOIN. This type of join returns all rows from the RIGHT-hand table specified in the ON condition and only those rows from the other table where the joined fields are equal (join condition is met). Syntax The syntax for the RIGHT OUTER JOIN in SQL Server (Transact-SQL) is: SELECT columns FROM table1 RIGHT OUTER JOIN table2 ON table1.column = table2.column; In some databases, the RIGHT OUTER JOIN keywords are replaced with RIGHT JOIN. Visual Illustration In this visual diagram, the SQL Server RIGHT OUTER JOIN returns the shaded area: The SQL Server RIGHT OUTER JOIN would return the all records from table2 and only those records from table1 that intersect with table2.

Example Here is an example of a RIGHT OUTER JOIN in SQL Server (Transact-SQL): SELECT orders.orderid, orders.orderdate, suppliers.suppliername FROM suppliers RIGHT OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; This RIGHT OUTER JOIN example would return all rows from the orders table and only those rows from the suppliers table where the joined fields are equal. If a supplierid value in the orders table does not exist in the suppliers table, all fields in the suppliers table will display as in the result set.

Let's look at some data to explain how RIGHT OUTER JOINS work: We have a table called suppliers with two fields (supplierid and suppliername). It contains the following data: supplierid suppliername 10000 Apple 10001 Google We have a second table called orders with three fields (orderid, supplierid, and orderdate). It contains the following data: orderid supplierid orderdate 50 2013/26 /27 /08/14 If we run the SELECT statement (that contains a RIGHT OUTER JOIN) below: SELECT orders.orderid, orders.orderdate, suppliers.suppliername FROM suppliers RIGHT OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; Our result set would look like this: orderid orderdate suppliername 5/08/12 Apple 5/08/13 Google 5/08/14 The row for 500127 (orderid) would be included because a RIGHT OUTER JOIN was used. However, you will notice that the suppliername field for that record contains a value.

FULL OUTER JOIN Another type of join is called a SQL Server FULL OUTER JOIN. This type of join returns all rows from the LEFT-hand table and RIGHT-hand table with nulls in place where the join condition is not met.

Syntax The syntax for the FULL OUTER JOIN in SQL Server (Transact-SQL) is: SELECT columns FROM table1 FULL OUTER JOIN table2 ON table1.column = table2.column; In some databases, the FULL OUTER JOIN keywords are replaced with FULL JOIN. Visual Illustration In this visual diagram, the SQL Server FULL OUTER JOIN returns the shaded area: The SQL Server FULL OUTER JOIN would return the all records from both table1 and table2. Example Here is an example of a FULL OUTER JOIN in SQL Server (Transact-SQL): SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers FULL OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; This FULL OUTER JOIN example would return all rows from the suppliers table and all rows from the orders table and whenever the join condition is not met, would be extended to those fields in the result set. If a supplierid value in the suppliers table does not exist in the orders table, all fields in the orders table will display as in the result set. If a supplierid value in the orders table does not exist in the suppliers table, all fields in the suppliers table will display as in the result set.

Let's look at some data to explain how FULL OUTER JOINS work: We have a table called suppliers with two fields (supplierid and suppliername). It contains the following data: supplierid suppliername 10000 IBM 10001 Hewlett Packard 10002 Microsoft 10003 NVIDIA We have a second table called orders with three fields (orderid, supplierid, and orderdate). It contains the following data: orderid supplierid orderdate 50 2013/26 /27 /08/14 If we run the SELECT statement (that contains a FULL OUTER JOIN) below: SELECT suppliers.supplierid, suppliers.suppliername, orders.orderdate FROM suppliers FULL OUTER JOIN orders ON suppliers.supplierid = orders.supplierid; Our result set would look like this: supplierid suppliername orderdate 10000 IBM 2013/1 Hewlett Packard 2013/2 Microsoft 10003 NVIDIA 2013/08/14 The rows for Microsoft and NVIDIA would be included because a FULL OUTER JOIN was used.

However, you will notice that the orderdate field for those records contains a value. The row for supplierid 10004 would be also included because a FULL OUTER JOIN was used. However, you will notice that the supplierid and suppliername field for those records contain a value.

By using joins, you can retrieve data from two or more tables based on logical relationships between the tables. Joins indicate how Microsoft SQL Server should use data from one table to select the rows in another table. A join condition defines the way two tables are related in a query by:. Specifying the column from each table to be used for the join. A typical join condition specifies a foreign key from one table and its associated key in the other table. Specifying a logical operator (for example, = or,) to be used in comparing values from the columns. Inner joins can be specified in either the FROM or WHERE clauses.

Outer joins can be specified in the FROM clause only. The join conditions combine with the WHERE and HAVING search conditions to control the rows that are selected from the base tables referenced in the FROM clause. Specifying the join conditions in the FROM clause helps separate them from any other search conditions that may be specified in a WHERE clause, and is the recommended method for specifying joins. A simplified ISO FROM clause join syntax is: FROM firsttable jointype secondtable ON ( joincondition) jointype specifies what kind of join is performed: an inner, outer, or cross join. Joincondition defines the predicate to be evaluated for each pair of joined rows.

The following is an example of a FROM clause join specification. SELECT ProductID, Purchasing.Vendor.BusinessEntityID, Name FROM Purchasing.ProductVendor JOIN Purchasing.Vendor ON (Purchasing.ProductVendor.BusinessEntityID = Purchasing.Vendor.BusinessEntityID) WHERE StandardPrice $10 AND Name LIKE N'F%' GO The select returns the product and supplier information for any combination of parts supplied by a company for which the company name starts with the letter F and the price of the product is more than $10. When multiple tables are referenced in a single query, all column references must be unambiguous. In the previous example, both the ProductVendor and Vendor table have a column named BusinessEntityID.

Any column name that is duplicated between two or more tables referenced in the query must be qualified with the table name. All references to the Vendor columns in the example are qualified.

When a column name is not duplicated in two or more tables used in the query, references to it do not have to be qualified with the table name. This is shown in the previous example. Such a SELECT statement is sometimes difficult to understand because there is nothing to indicate the table that provided each column. The readability of the query is improved if all columns are qualified with their table names. The readability is further improved if table aliases are used, especially when the table names themselves must be qualified with the database and owner names.

Using Self-Joins

The following is the same example, except that table aliases have been assigned and the columns qualified with table aliases to improve readability. SELECT pv.ProductID, v.BusinessEntityID, v.Name FROM Purchasing.ProductVendor AS pv, Purchasing.Vendor AS v WHERE pv.VendorID = v.VendorID AND StandardPrice $10 AND Name LIKE N'F%'; The select list for a join can reference all the columns in the joined tables, or any subset of the columns. The select list is not required to contain columns from every table in the join. For example, in a three-table join, only one table can be used to bridge from one of the other tables to the third table, and none of the columns from the middle table have to be referenced in the select list. Although join conditions usually have equality comparisons (=), other comparison or relational operators can be specified, as can other predicates. For more information, see and. When SQL Server processes joins, the query engine chooses the most efficient method (out of several possibilities) of processing the join.

Left Outer Join Syntax Oracle

The physical execution of various joins can use many different optimizations and therefore cannot be reliably predicted. Columns used in a join condition are not required to have the same name or be the same data type. However, if the data types are not identical, they must be compatible, or be types that SQL Server can implicitly convert. If the data types cannot be implicitly converted, the join condition must explicitly convert the data type using the CAST function. For more information about implicit and explicit conversions, see. Most queries using a join can be rewritten using a subquery (a query nested within another query), and most subqueries can be rewritten as joins. For more information about subqueries, see.

Note Tables cannot be joined directly on ntext, text, or image columns. However, tables can be joined indirectly on ntext, text, or image columns by using SUBSTRING. For example, SELECT. FROM t1 JOIN t2 ON SUBSTRING(t1. Textcolumn, 1, 20) = SUBSTRING(t2. Textcolumn, 1, 20) performs a two-table inner join on the first 20 characters of each text column in tables t1 and t2.

In addition, another possibility for comparing ntext or text columns from two tables is to compare the lengths of the columns with a WHERE clause, for example: WHERE DATALENGTH(p1.prinfo) = DATALENGTH(p2.prinfo).