Oracle update subquery factoring

Specify an expression representing the value or values of the cell or cells specified on the right-hand side of the rule. ALL is the default. This clause defines a read-only multidimensional array based on the results of a query. The number and data types of the columns selected by each component query must be the same, but the column lengths can be different. The names of the columns in the result set are the names of the expressions in the select list preceding the set operator.

If you combine more than two queries with set operators, then the database evaluates adjacent queries from left to right. The parentheses around the subquery are optional.

You can use them to specify a different order of evaluation. The expression is based on columns in the select list or columns in the tables, views, or materialized views in the FROM clause. The position value must be an integer. Oracle Database first sorts rows based on their values for the first expression. Rows with the same value for the first expression are then sorted based on their values for the second expression, and so on. The database sorts nulls following all others in ascending order and preceding all others in descending order.

Refer to "Sorting Query Results" for a discussion of ordering query results. ASC is the default. Expressions comprising the preceding expressions that evaluate to the same value for all rows in a group. Nested table rows are not locked as a result of locking the parent table rows. If you want the nested table rows to be locked, then you must lock them explicitly. The tables locked by this clause must all be located on the same database and on the same database as any LONG columns and sequences referenced in the same statement.

This occurs when the view has been merged to its containing query block internally by the query optimizer, and SELECT Use the OF The columns in the OF clause only indicate which table or view rows are locked. The specific columns that you specify are not significant. However, you must specify an actual column name, not a column alias. If you omit this clause, then the database locks the selected rows from all the tables in the query.

Specify WAIT to instruct the database to wait integer seconds for the row to become available and then return control to you. This feature is designed for use in multiconsumer queue environments, such as Oracle Streams Advanced Queuing. It enables queue consumers to skip rows that are locked by other consumers and obtain unlocked rows without waiting for the other consumers to finish.

Recursive Subquery Factoring: Examples The following statement shows the employees who directly or indirectly report to employee and their reporting level. The following statement shows employees who directly or indirectly report to employee , their reporting level, and their management chain.

The following statement shows the employees who directly or indirectly report to employee and their reporting level. It stops at reporting level 1.

Simple Query Examples The following statement selects rows from the employees table with the department number of The following statement selects the name, job, salary and department number of all employees except purchasing clerks from department number The following statement selects from subqueries in the FROM clause and for each department returns the total employees and salaries as a decimal value of all the departments:.

The following example selects rows from the oe. Selecting a Sample: Examples The following query estimates the number of orders in the oe. Because the query returns an estimate, the actual return value may differ from one query to the next. The following query adds a seed value to the preceding query. Oracle Database always returns the same estimate given the same seed value:.

Using Flashback Queries: Example The following statements show a current value from the sample table hr. The intervals used in these examples are very short for demonstration purposes. Time intervals in your own environment are likely to be larger.

To learn what the values were during a particular time period, you can use a version Flashback Query:. To return the minimum and maximum salaries for the clerks in each department, issue the following statement:. The following example uses a correlated subquery in a HAVING clause that eliminates from the result set any departments without managers and managers without departments:. To select information from employees ordered first by ascending department number and then by descending salary, issue the following statement:.

It also:. Assigns the sum of the sales of the Mouse Pad for years and to the sales of the Mouse Pad for year , if a row containing sales of the Mouse Pad for year exists. Assigns the value of sales of the Standard Mouse for year to sales of the Standard Mouse for year , creating a new row if a row containing sales of the Standard Mouse for year does not exist.

The rows represented by the left-hand side of the rule exist, so the measure columns are updated. If the rows did not exist, then no action would have been taken. The second rule uses UPSERT behavior because positional referencing is used on the left-hand side and a single cell is referenced.

The rows do not exist, so new rows are inserted and the related measure columns are updated. If the rows did exist, then the measure columns would have been updated. The following statement locks only those rows in the employees table with purchasing clerks located in Oxford.

No rows are locked in the departments table:. The UNPIVOT clause lets you rotate specified columns so that the input column headings are output as values of one or more descriptor columns, and the input column values are output as values of one or more measures columns.

The first query that follows shows that nulls are excluded by default. Using Join Queries: Examples The following examples show various ways of joining tables in a query. In the first example, an equijoin returns the name and job of each employee and the number and name of the department in which the employee works:. You must use a join to return this data because employee names and jobs are stored in a different table than department names.

Oracle Database combines rows of the two tables according to this join condition:. The following equijoin returns the name, job, department number, and department name of all sales managers:. Using Subqueries: Examples To determine who works in the same department as employee ' Lorentz ', issue the following statement:. Using Self Joins: Example The following query uses a self join to return the name of each employee along with the name of the employee's manager.

The join condition for this query uses the aliases e1 and e2 for the sample table employees :. Using Outer Joins: Examples The following example shows how a partitioned outer join fills data gaps in rows to facilitate analytic function specification and reliable report formatting. The example first creates a small data table to be used in the join:.

Users familiar with the traditional Oracle Database outer joins syntax will recognize the same query in this form:. Oracle strongly recommends that you use the more flexible FROM clause join syntax shown in the former example. The left outer join returns all departments, including those without any employees.

The same statement with a right outer join returns all employees, including those not yet assigned to a department:. To determine this requires a full outer join:. Because the column names in this example are the same in both tables in the join, you can also use the common column feature by specifying the USING clause of the join syntax.

Using Partitioned Outer Joins: Examples The following example shows how a partitioned outer join fills in gaps in rows to facilitate analytic calculation specification and reliable report formatting.

The example first creates and populates a simple table to be used in the join:. The data is now more dense along the time dimension for each partition of the product dimension.

However, each of the newly added rows within each partition is null in the quantity column. It is more useful to see the nulls replaced by the preceding non- NULL value in time order. Using Antijoins: Example The following example selects a list of employees who are not in a particular set of departments:. Using Semijoins: Example In the following example, only one row needs to be returned from the departments table, even though many rows in the employees table might match the subquery.

If no index has been defined on the salary column in employees , then a semijoin can be used to improve query performance. Table Collections: Examples You can perform DML operations on nested tables only if they are defined as columns of a table.

The examples that follow are based on the following scenario:. Collection Unnesting: Examples To select data from a nested table column, use the TABLE collection expression to treat the nested table as columns of a table. This process is called collection unnesting. You can extract the same rows as in the preceding example with this statement:.

You can get the same information as in the preceding examples with the following query:. The child rows of a parent row are defined to be those who have the employee number of the parent row as their manager number.

Oracle Database does not return the manager Greenberg , although it does return employees who are managed by Greenberg. The following statement is similar to the first one, except that it uses the LEVEL pseudocolumn to select only the first two levels of the management hierarchy:. Using Distributed Queries: Example This example shows a query that joins the departments table on the local database with the employees table on the remote database:.

Using Correlated Subqueries: Examples The following examples show the general syntax of a correlated subquery:.

The following statement returns data about employees whose salaries exceed their department average. The following statement assigns an alias to employees , the table containing the salary information, and then uses the alias in a correlated subquery:.

Such queries are difficult to read, hard to maintain, and a nightmare to optimize. In Oracle database the WITH clause is used for materializing subqueries to avoid recomputing them multiple times without using temporary tables. The WITH clause allows factor out a sub-query, name it, and then reference it by name multiple times within the original complex query.

Additionally this technique lets the optimizer choose how to deal with the sub-query results -- whether to create a temporary table or inline it as a view.

Oracle actually does not create table but merge SQL before execution. In other words WITH clause allows us to name a predefined Select statement in the context of a bigger Select and referenced in later by the given name. Reference a named query is allowed any number of times. Any number of named queries are allowed. Named queries can reference other named queries that came before them and even correlate to previous named queries.

The bold text represents the parts of the query that are repeated. The bold text represents the common parts of the subquery, and the places where the subquery is referenced. This is because many queries will be treated by Oracle as an in-line view. This means that following execution of the same cursor will result in a new temp table each time. The problem is that to get the result, table is accessed twice. To avoid this we could refactor the query using WITH clause.

As was said above there will be a single access due to materialization of the recordset. Here is the syntax for using subquery factoring in DML:. Burleson is the American Team Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.

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