The following query can be an example of this usage method. We have typed the Persons table after the MERGE statement because it is our target table, which we want to update, and we gave Per alias to it in order to use the rest of the query. With the help of this syntax, the join condition is defined between the target and source table. In this last line of the query, we chose the manipulation method for the matched rows. Finally, we added the semicolon ; sign because the MERGE statements must end with the semicolon signs.
The major characteristic of the subquery is, they can only be executed with the external query. The noticeable difference in this method is, it might be a convenient way to update one column for the tables that have a small number of the rows. Now we will execute the following query and then will analyze it.
After the execution of the update from a select statement the output of the table will be as below;. As we can see, the PersonCityName column data of the Persons table have been updated with the City column data of the AddressList table for the matched records for the PersonId column.
Regarding this method, we should underline the following significant points. If the subquery finds more than one matched row, the update query will return an error, as shown below:. In this article, we learned to update the data in a table with the data where they are contained in other tables.
PersonId INT. PersonName , PersonLastName. N 'Salvador' , N 'Williams' ,. N 'Lawrence' , N 'Brown' ,. N 'Gilbert' , N 'Jones' ,. N 'Ernest' , N 'Smith' ,. N 'Jorge' , N 'Johnson'. PersonId , PostCode , City. City ,. AddressList Addr. The previous subquery in this statement cannot be evaluated independently of the outer query. It needs a value for Employee. That is exactly how this query is evaluated: SQL Server considers each row of the Employee table for inclusion in the results by substituting the value in each row into the inner query.
These two query samples represent a decomposition of the previous sample with the correlated subquery. The result is 0. Because this is false, the row for Syed Abbas is not included in the results of the previous sample query with the correlated subquery. Go through the same procedure with the row for Pamela Ansman-Wolfe. Correlated subqueries can also include table-valued functions in the FROM clause by referencing columns from a table in the outer query as an argument of the table-valued function.
In this case, for each row of the outer query, the table-valued function is evaluated according to the subquery. Many statements in which the subquery and the outer query refer to the same table can be stated as self-joins joining a table to itself.
For example, you can find addresses of employees from a particular state using a subquery:. Table aliases e1 and e2 are required because the table being joined to itself appears in two different roles. Aliases can also be used in nested queries that refer to the same table in an inner and outer query.
Explicit table aliases make it clear that a reference to Person. Address in the subquery does not mean the same thing as the reference in the outer query. After the subquery returns results, the outer query makes use of them. The following query finds the names of all the wheel products that Adventure Works Cycles makes. This statement is evaluated in two steps.
First, the inner query returns the subcategory identification number that matches the name 'Wheel' Second, this value is substituted into the outer query, which finds the product names that go with the subcategory identification numbers in Production.
One difference in using a join rather than a subquery for this and similar problems is that the join lets you show columns from more than one table in the result. For example, if you want to include the name of the product subcategory in the result, you must use a join version. The following query finds the name of all vendors whose credit rating is good, from whom Adventure Works Cycles orders at least 20 items, and whose average lead time to deliver is less than 16 days.
The inner query is evaluated, producing the ID numbers of the vendors who meet the subquery qualifications. The outer query is then evaluated. Notice that you can include more than one condition in the WHERE clause of both the inner and the outer query. A join can always be expressed as a subquery. A subquery can often, but not always, be expressed as a join. This is because joins are symmetric: you can join table A to B in either order and get the same answer.
The same is not true if a subquery is involved. The following query finds the names of the products that are not finished bicycles. This statement cannot be converted to a join.
The analogous not-equal join has a different meaning: It finds the names of products that are in some subcategory that is not a finished bicycle. The following example doubles the value in the ListPrice column in the Production. If you want to update b , the statement will be:. The statement below will delete from a only leaving b intact for those records that match by name:. Here in my sample I find out the solution of this, because I had the same problem with updates and subquerys:.
The title of this thread asks how a subquery can be used in an update. Here's an example of that:. Here is a nice explanation of update operation with some examples. The following examples are intuitive to understand. However, the second query may give unexpected results if salesmen. Also, if there is no match for a particular accounts. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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