oracle sql tuning tips

Tips for using functions in Oracle (2)-The NULLIF function provides the abbreviated CASE expression through a comparison expression. Syntax NULLIF (expression-1, expression-2) the expression to be compared with expression-1. Expression-2: The expression to be compared. Use NULLIF to compare the values of two expressions. If the value of the first expression is equal to that of the second expression, NULLIF

their estimated values.You can use the ordered_predicates prompt to forcibly replace these default evaluation rules. The items in your WHERE clause will be evaluated in the order they appear in the query. When PL/SQL functions are used in the WHERE clause, the ordered_predicates prompt is usually used. If you know the most restrictive judgments and want Oracle to evaluate them first, it is also very useful

their definition does not paste and be changed. Contention for a latch increases the execution time of the statement and reduces concurrency. Soft parsing any ill-resolved parsing isSoft parsing。 If you submit a statement that is the same as a reusable SQL statement in a shared type, the database reuses that existing code. Reuse code is also known asLibrary Cache Hit。 General, soft parsing is preferable to hard parsing because the database can

Label:To quickly use PL/SQL developer for Oracle database-related development, summarize some of the more frequently used tips below, from the network and your own tests 1. Switch schema --switch SchemaAlter session set current_schema= PO; --get Current Context informationSelectSys_context ('USERENV','Current_User') Current_User, Sys_context ('USERENV','Curren

> $total? 1: $start _row; $end _row = $start _row + $rows-1; $end _row = $end _row > $total? $total: $end _row; $query = "SELECT * from" (select RowNum as Row_num, r.* from ($query) r WHERE rownum Main two methods I write a little note Second, call the method $total = $this->db->getcount ($sql); $result = $this->db->getpage ($sql, $total, $page, $page _number); It just posted part of

With SPA, you can play a specific stream based on various types of changes (such as initialization parameter changes, optimizer statistics refresh, and database upgrades)SQL or the entire SQL load, and then generate a comparison report to help you evaluate their impact. In versions earlier than Oracle Database 11g, I must capture all

Tags: http io ar using SP strong on data artA colleague of mine, Martin Masarik,sqlde's CEO, talked to me about one of his DBA friends who managed an Oracle database for an international bank with a data size of about 2TB. Martin Masarik once asked him: "What kind of SQL problem can make you angry to hair-up?" He summed up the following points, all of which are experience:First, do not invoke function on th

you limit the number of indexes in the table. For tables that are primarily for reading, there are many advantages to indexing, but if a table is frequently changed, the index should be less.10. Creates an index after inserting data into the table. If an index is created before the data is loaded, Oracle must change each index when each row is inserted.Three, long type (can store 2G) is mainly used to do not need to do string search long string of da

procedures)SQL code Create procedure Xiaozhengge @sqlstr nvarchar (4000), --query string @currentpage int, --page n @pagesize int --Number of rows per page As SET NOCOUNT on DECLARE @P1 int, --P1 is the ID of the cursor @rowcount int EXEC sp_cursoropen @P1 output, @sqlstr, @scrollopt =1, @ccopt =1,@[email protected] output Select Ceiling (1.0* @rowcount/@pagesize) as total number of pages--, @rowcount as rows, @currentpage

relatively easy, and your eyes will thank you. Setup method: Menu Tools --Preferences---Keyword case-to-uppercase5. Special CopySQL is written in SQL window usually need to put in Java or other languages, you need to turn into a string and add the corresponding hyphen, this thing does not need to repeat, in the written SQL right-click, using special copy is ok! Setup Method: Right--Special Copy6. Custom sh

Oracle offers a number of ways to reduce the time spent parsing Oracle SQL expressions, which can drag down the system's performance when performing complex queries with a large number of execution plans. Now let's take a brief look at several of these methods. 1. Use ordered Tips

Oracle offers a number of ways to reduce the time spent parsing Oracle SQL expressions, which can drag down the system's performance when performing complex queries with a large number of execution plans. Now let's take a brief look at several of these methods. 1. Use ordered tips

oracle| optimization 1. The statements that have been validated are exactly the same as those already in the shared pool 2. Variable names as consistent as possible 3. Rational use of outer joins 4. Use fewer layers of nesting 5. Multi-use concurrency The optimization steps for a statement are generally: 1. The SGA area is adjusted so that the SGA area is optimally used. 2. optimization of the SQL statemen

limit 1)); Error 1105 (HY000): XPATH syntax error: ' \admin888 ' mysql> select * from article WHERE id = 1 and 1= (Updatexml (1,concaT (0x5e24, (select pass from admin limit 1), 0x5e24), 1)); Error 1105 (HY000): XPATH syntax error: ' ^ $admin 888^$ 'In other databases, you can use different methods to make an error.PostgreSQL:/?param=1 and (1) =cast (version () as numeric)--MSSQL:/?param=1 and (1) =convert (int,@ @version)--Sybase:/? Param=1 and (1) =convert (int,@ @version)--

(x, y); x> y returns a positive number, indicating the number of months between x and y (not used in the actual project, too many records are not made for the time being ). String processing functions: 6) nvl (x, value). If x is null, return the value in value; otherwise, return x; 7), length (x), returns the length of x; (8) substr (x, start, length) truncates string x. The length starting from start is length; if you need to take the following digits of the string, you can write as follows:

With the SPA, you can play specific types of changes depending on the type of change (such as initialization of change, optimizer statistics refresh, and database upgrade)SQL or the entire SQL payload, and then generate a comparison report that helps you evaluate their impact.In the version number prior to Oracle Database 11g, I had to capture all the

SQL Group by summary for Oracle databasesPrefaceAs mentioned above, grouping Functions Act on a group of records. What can this group of records be generated? ImpossibleThey are all in the form of a whole table. This requires the Group by clause.GroupGroup by clause:● The Group by clause divides a table into multiple groups and returns a calculated value for each Group.● Group by expression: indicates the c

database is commonly used for testing purposes Select 'OK' fromdual; Spooloff; --This also must, otherwise, after the script execution completes, will hang in the Sqlplus command line, does not exit Exit; Look at a few SQL stored procedures, note that some display a row, some display the name, and some display content: Select name from User_source where type= ' PROCEDURE '; Select text from all_source where name = ' Pro_name '; SELECT * from User_pr

.) You can use records to retrieve information from the returning clause of DML statements. It is usually useful to keep a local copy when updating data for subsequent PL/SQL operations. Before Release 2, we can use the returning clause to store data somewhere after computation and call are complete. In Release 2, data can be stored in a record. For example, the following is the practice before release 2: DeclareFoorow footab % rowtype;BeginInser

indexes and multiple individual indexes: Consider the number of times the index is read selectively considering and-equal Operation3Manage multiple table connections (Nested Loops, merge Joins and hash Joins) optimize join operations Merge Joins is a collection operation Nested Loops and Hash Joins is a record operation returns the first batch of records quickly merge J Oins operation for batch operations, huge tables and remote queries 1 full table scan--〉2 Sort--The 〉3 Compare and merge perfo