Oracle Pl Sql Tips And Tricks Pdf

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oracle pl sql tips and tricks pdf

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Yes, there are a LOT of options.

PL/SQL Tutorial

All other values should remain the same as substitution condition is not met. Translating requirements from English to SQL will likely result in a bulky and inefficient query. Can we do better than that? Yes, we can! I strongly recommend executing parts of the above queries to gain a better understanding of the demonstrated strategies.

Would you like to read about many more tricks and puzzles? In the previous blog post on that subject we reviewed a couple a notable applications of Oracle analytic functions. Today, I came across another interesting illustration of the same concept. Like before, we start with traditional approaches that every experienced developer would easily demonstrate.

As we have seen before, with analytic functions, we can get away with a single copy of th emp table. We need to use LIKE operator in case we have more than a single Adams working in the same department and holding the same job title. Analytic functions are still underutilized among database developers. The goal of this publication is to demonstrate hidden opportunities to improve query performance by using analytic functions where traditional approach is still dominating.

Problem 1: Find all employees from the department where a top paid clerk works. Traditional approach suggests finding the department 10 first and then the task becomes trivial:. OK, that works, but now we need to produce a query that will get us that department number of several ones if they all have top paid clerks.

There are many ways of finding a top record with and without analytic functions. The use of analytic functions reduces the number of table copies as we can get all the necessary details in a single table scan as in the following query:. Yes, it works, but what an overkill! Is it still possible to use a single emp table scan to solve this problem? The answer is YES:. The OVER clause gives us either department level top salary or global top salary value for the clerks.

And since it is done on a row level, which means that the these analytic functions return the same values for all employees in the same department, we can achieve our goal easily. MAX function is not the only one analytic function that can be used here.

Problem 2: Find employees who are paid above the average salary in their respective department. An experienced developer would quickly see that this problem can be solved with the same approach as the problem 1 above :. The problem was discussed in one of my old blog posts and I strongly suggest you to check it out: A trick that helps avoiding multiple table scans.

List all days from today till the last day of the week. The query should work regardless of the regional settings that affect first day of the week, whether it is Sunday, Monday, or any other day.

The trick here is not to attempt figuring out the current day of the week, whether it is Friday, Saturday or anything else. We need to apply a date function that returns the same value or is constantly staying in the same interval for all the days within the same week. In a traditional scott. Both solutions above use 2 copies of the emp table which makes oracle scan the same scott. A trick presented below allows you to use only a single copy of the emp table to solve the problem.

The trick involves different conceptual and technical approaches compared to the solutions we have seen so far. Conceptually, we should rephrase the problem in a way that would keep it identical and at the same time allows us to use different technical arsenal. We do need to use a common table expression as we cannot filter out by analytic function in the same query where the function is used.

Nevertheless, we scan the emp table just once , and during this scan, Oracle engine counts the number of presidents in each department. Instead of counting the presidents by department, we simply concatenate all the job titles and check if the resulting string includes a president. SIGN on top of what we used in Strategy 3 as a secondary dimension and empno as primary. Employee number is unique by itself, so adding another dimension will still maintain uniqueness required by MODEL clause.

You can check the execution plan for all of the above strategies to see how many times Oracle scans the emp table. Here is a simplified version of that code:. This code will only work if the sequence already exists before you run this block. If you try the following line, it will throw an exception:. We will start with the in-line scalar subquery approach as it is probably one of the most intuitive:.

If we needed more than one: count and let say total salary, we would need to use LATERAL view or a completely different approach — see below.

So far, all is good. Can it be applied in the lateral view? Essentially, our last incorrect query is the same as the following:. The above examples prove that we need to be very careful when mixing up different techniques and new syntax options. Finally, the last approach will show that only a single scan of the emp table is needed to get the result:. This is the best and incidentally the shortest solution that once again demonstrates the power of conditional counting aggregation right in SELECT clause.

I was looking for an answer to this question for quite some time and ended up developing my own approach. As of version We can pass arbitrary number of values into such constructors. It can take more or less values as well. Here is how we could use sys. The use of sys. You can pass as many arguments to the constructor as you wish. To make things look a bit prettier, we can create a short synonym:. Use scott. The answer is NO! It would become apparent if we had a department where all employees get paid commission, so the number of those who does not would be 0.

So how should we work around? Essentially, the original problem transforms into a new one — find all department where no employees were hired on Friday. Cartesian product.

All the above techniques may look cool but they are clearly an overkill for such a simple problem. There is a simple rule worth remembering:.

You can read more about it in my recent post here. Search Search for:. SQL Puzzle of the day: List all days from today till the last day of the week. COUNT is not the only analytic function that can be employed to solve the problem. This applies to all kinds of objects. For example, if you create a table in your procedure, you may only select from this table in dynamic SQL.

If you dynamically add a column to a table, you can only update it in dynamic SQL, etc. If you find this post useful, please press the LIKE button and subscribe. As you know, Oracle allows altering more than one column in a single command. Previous Articles. By continuing to use this website, you agree to their use. To find out more, including how to control cookies, see here: Cookie Policy.

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Top 10 Tips & Tricks for Oracle SQL Developer

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the Oracle Database, the other two being SQL and Java. Page 6. Tips and Techniques. • Oracle SQL Developer: SQL Worksheet. •.


PL/SQL Tutorial: Learn Oracle PL/SQL in 7 Days

Before you start fidgeting with individual SQL statements, it is important to note that hints are probably the last thing you should consider adding when attempting to optimize your code. There are several levels of optimization and it is recommended that you start with the server, then the database instance, and finally go down through the database objects to individual statements. After all, the effect of any changes made to individual statements, particularly hints, may be lost when the database is fine-tuned later on. Fortunately, there is a bunch of things you can do to improve the runtime performance of your statements:. One important thing to keep in mind is that you should always strive to write efficient, legible code, but that premature optimization is not the way to go.

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When table column contains LONG type, batch update process is not performed. Fails due to SQL exception. Oracle how to update a table from a another table database. Oracle-base updates based on queries. Sql update statement.

PL/SQL Tutorial

Section 1. Getting started with PL/SQL

Молоденькая, изысканной внешности, ну прямо сошла со страниц журнала Севентин. Довольно консервативные брюки в клетку, белая блузка без рукавов. В руке красная туристская сумка фирмы Л. Белл. Светлые волосы тщательно уложены. - Прошу меня извинить, - пробормотал Беккер, застегивая пряжку на ремне.

Стратмор покачал головой. - Я попросил его не звонить мне, пока он не найдет кольцо. - Почему? - удивилась Сьюзан.  - А если ему нужна помощь. Стратмор пожал плечами.

 - Он сказал, что у них все в порядке. Фонтейн стоял, тяжело дыша. - У нас нет причин ему не верить.  - Это прозвучало как сигнал к окончанию разговора. Он отпил глоток кофе.

Камера вдруг повернулась к укрытию Халохота. Убийцы там уже не .

Ты займешься Третьим узлом. Сотрешь всю электронную почту Хейла. Все, что относится к его переписке с Танкадо, где упоминается Цифровая крепость. - Хорошо, - сказала Сьюзан, стараясь сосредоточиться, - я сотру весь накопитель Хейла. И все переформатирую.

Я прав. Сеньор Ролдан уловил некоторое замешательство на другом конце провода. - Ну, на самом деле .

Попробовал добрести до двери. Меган скрылась во вращающейся секции, таща за собой сумку. Беккер почти вслепую приближался к двери. - Подожди! - крикнул .

То, что она увидела, казалось неправдоподобным.

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    PL/SQL Tips & Tricks. Daniel A. Morgan | [email protected] | www.​gilariverdistrict.org Edition Based Redefinition in Oracle Database 11gR2.

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    Since PL/SQL. Version 2 was first released, for example, Oracle. Corporation has added dynamic SQL, RDBMS-based job scheduling, file I/O, and cursor variables​.

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