Hi, Nathan : Queue processing is always tricky. Assuming that the batch-id is a worker-chunk id i. Your examples have some strange parts, like updating to state 'Y' but then fetching the state 'N' rows? It was internally developed by Oracle for their AQ-system and only later opened for public use. We feel it never reached general production state probably because Oracle uses it only in exactly the way for which it was implemented which we don't know, so we usually end up misusing it unknowingly.
We switched to hard locking with repeated retries wherever it is necessary. Our main queueing system however doesn't need it to form chunks because our workload comes in many simultaneous types so we can do the chunking per type after locking on the type thus getting parallel throughput without meeting on the same rows. Only processing, which as usual happens per chunk i.
But with on average rows per chunk this is tolerable compared with locking on the original rows. Hi All, We are trying to implement concurrent approach but I found that sometimes same records are inserted if we call the procedure parallel. When the record fetched the stat column will be updated to Y in emp table.
It is given demo tables actually we have tested for records and out of that records fetched by 2 jobs with seconds interval gaps. As the lock happening whenever fetched instead of opening of cursor is reason of the scenario is going wrong. April 04, - am UTC. Alternation matches a single regular expression from a list of several possible regular expressions.
Alternatives are preferred in the order they are specified. If A is not matched, then it attempts to match B. If B is not matched, then it attempts to match C. This clause lets you specify a row pattern term.
A row pattern term can take one of the following forms:. The syntax used in the second and third examples represents concatenation. Concatenation is used to list two or more items in a pattern to be matched and the order in which they are to be matched. Only rows that match A , B , and C , are included in the row pattern match. This clause lets you specify a row pattern factor.
Use this clause to specify the row pattern element. Table lists the valid row pattern elements and their descriptions. This element is an anchor. Anchors work in terms of positions rather than rows.
An empty pattern matches an empty set of rows. Exclusion syntax. Note that the row pattern elements are expanded lexicographically and that each element to permute must be separated by a comma from the other elements. Oracle Database Data Warehousing Guide for more information on permutations. Use this clause to specify the row pattern quantifier, which is a postfix operator that defines the number of iterations accepted for a match.
Row pattern quantifiers are referred to as greedy; they will attempt to match as many instances of the regular expression on which they are applied as possible. The exception is row pattern quantifiers that have a question mark? They will attempt to match as few instances as possible of the regular expression on which they are applied.
Table lists the valid row pattern quantifiers and the number of iterations they accept for a match. In this table, n and m represent unsigned integers.
Oracle Database Data Warehousing Guide for more information on row pattern quantifiers. This clause lets you create a grouping of multiple pattern variables that can be referred to with a variable name of its own.
The variable name that refers to this grouping is called a union row pattern variable. On the right side of the equal sign, specify a comma-separated list of distinct primary row pattern variables within parentheses. This list cannot include any union row pattern variables.
Oracle Database Data Warehousing Guide for more information on defining union row pattern variables. A row pattern definition specifies the conditions that a row must meet in order to be mapped to a specific pattern variable.
Oracle Database Data Warehousing Guide for more information on running and final semantics. This clause lets you specify a row pattern definition, which contains the conditions that a row must meet in order to be mapped to the specified pattern variable. This clause comprises the following clauses, which let you specify row pattern recognition functions:. These details are explained in the semantics for each clause.
Matches within a row pattern partition are numbered sequentially starting with 1 in the order in which they are found. If multiple rows satisfy a match, then they are all assigned the same match number.
Note that match numbering starts over again at 1 in each row pattern partition, because there is no inherent ordering between row pattern partitions. The FIRST function returns the value of expression expr when evaluated in the first row of the group of rows mapped to the pattern variable that is specified in expr.
The LAST function returns the value of expression expr when evaluated in the last row of the group of rows mapped to the pattern variable that is specified in expr.
Use expr to specify the expression to be evaluated. It must contain at least one row pattern column reference. If it contains more than one row pattern column reference, then all must refer to the same pattern variable. Use the optional offset to specify the logical offset within the set of rows mapped to the pattern variable. When specified with the FIRST function, the offset is the number of rows from the first row, in ascending order.
When specified with the LAST function, the offset is the number of rows from the last row in descending order. The default offset is 0. For offset , specify a non-negative integer. It must be a runtime constant literal, bind variable, or expressions involving them , but not a column or subquery. If you specify an offset that is greater than or equal to the number of rows mapped to the pattern variable minus 1, then the function returns NULL.
The PREV function returns the value of expression expr when evaluated in the previous row in the partition. The NEXT function returns the value of expression expr when evaluated in the next row in the partition.
Use the optional offset to specify the physical offset within the partition. When specified with the PREV function, it is the number of rows before the current row. When specified with the NEXT function, it is the number of rows after the current row.
The default is 1. If you specify an offset of 0, then the current row is evaluated. This clause lets you use an aggregate function in the expression for a row pattern measure column or in the condition that defines a primary pattern variable. Oracle Database Data Warehousing Guide for more information on aggregate functions.
The macro function budget computes the amount of each department's budget for a given job. It returns the number of employees in each department with the specified job title. Subquery Factoring: Example. 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. It stops at reporting level 1. The results of the selection are filtered to those for the YEAR level of the hierarchy.
The results are returned in hierarchical order. The following statement defines an inline analytic view in the FROM clause. 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:.
Selecting from a Partition: Example. 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 each department in the employees table, issue the following statement:. To return the minimum and maximum salaries for the clerks in each department, issue the following statement:. To return the number of employees and their average yearly salary across all possible combinations of department and job category, issue the following query on the sample tables hr.
Hierarchical Query Examples. 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 all purchasing clerk records from employees and order the results by salary in descending order, issue the following statement:. To select information from employees ordered first by ascending department number and then by descending salary, issue the following statement:.
The view created below is based on the sample sh schema and is used by the example that follows. 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. Row Limiting: Examples. Because WITH TIES is specified, the following statement returns the 5 percent of employees with the lowest salaries, plus all additional employees with the same salary as the last row fetched in the previous example:.
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 oe. 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:. The employee Zeuss was added to the employees table for these examples, and is not part of the sample data.
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:. That's why I used 0. You need to over-sample a little bit to ensure that you get more than N. How much do you need to over-sample? I have no idea, you'll probably have to test it and pick a safe number. You need to know the approximate number of rows to pick the percent. The percent must be a literal, so as the number of rows and N change, you'll need to use dynamic SQL to change the percent.
Jon Heller Jon Heller It's good to mention though for those with an overwhelming need for premature optimization. Elapsed: Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. Sometimes you need a table with N rows as a seed for a dataset.
The content of the records doesn't matter. They just need to be there. For example, suppose you need a table with enough records to create a record for each day of this year, how would you go about it? Also see the forum page: row generator. As it is discussed in Oracle Magazine Sept. This is straightforward but How many rows should you create to satisfy your needs? Is enough? This article discusses several ways of making things more flexible. Then we could do the following:.
You could use a Cartesian join to increase the number of records returned.
0コメント