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five records at the physical location. There will be two
Case:First, if the order by field is not a primary key, only order by is performed.Second, if the order by field is the primary key, sort the result set by and calculate rownum.
However, in the industrial environment, it is impossible to sort the primary keys all the time. Therefore, we can sort non-primary keys Through instantiation.[Code = SQL] [/Code]
SQ
Introduction to the use of dual tables in Oracle and the use of oracledual tables
Dual is a virtual table used to form the select syntax rule. oracle ensures that there will always be only one record in dual. We can use it to do a lot of things, as shown below:
1. view the c
Tags: relational database BSP SQ data very from extended ROS environment
Oracle Database:
Oracle Database, also known as Oracle RDBMS, or Oracle. is a relational database management system of Oracle Corporation. It is a leading product in the field of
ordered_predicates, Oracle uses the following steps to evaluate the order of SQL judgment:
The evaluation of a subquery is prior to the Boolean condition in the outer WHERE clause.
All Boolean conditions without built-in functions or subqueries are evaluated in the reverse order of the WHERE clause. That is, the last condition is evaluated first.
Boolean judgments with built-in functions are sorted in asce
SQL Optimization Tips (1):Connection order in the WHERE clause: Oracle parses the WHERE clause in a bottom-up order, and according to this principle, the connections between tables must be written before other where conditions, those that can filter out a large number of recordsMust be written at the end of the WHERE clause.For exampleInefficient: SELECT * from Report_sale_account Ewhere hsje>5000and DZXL =
database name. Here, you can enter the correct one, you can also enter it at will or leave it blank. After installation is complete, configure it again. After installation, the configuration listening page is displayed. Click Cancel. The installation process is similar to DB installation or client installation.
Iv. Configure the transparent gateway parameter file
Find the transparent gateway path: D: \ oracle \ product \ 10.2.0 \ tg_1 \ tg4msql \ adm
clause.(3) Avoid using '*' in the select clause '*':During the parsing process, Oracle converts '*' into all column names in sequence. This is done by querying the data dictionary, which means it takes more time.(4) Reduce the number of visits to the database:Oracle has performed a lot of internal work: parsing SQL statements, estimating index utilization, binding variables, and reading data blocks;(5) re-
oracle optimizer as much as possible and provide conditions for it;Suitable indexes, Double Effects of indexes, and column selectivity;3. encoding:Use indexes to avoid full table scan for large tables;Rational use of temporary tables;Avoid writing too complex SQL statements, not necessarily requiring one SQL statement
Obtain SQL Execution plans from the most authoritative Oracle Database
This document is compiled and summarized based on relevant information. It mainly describes the most authoritative and correct methods and steps for obtaining SQL statement execution plans in Oracle databases. In addition, the meanings and usage of
Database: SQL Server 2008, Oracle 9iTool: trial version of Sybase powerdesiner 12, PL/SQL developer 7.1.5
There are two main tasks for Migration:1. Generate a script for creating an Oracle database based on the SQL Server database2. ModifyCodeSQL statement in
Generate a
Label:Let's start a new chapter to learn! When an SQL statement is entered, the statement is present in the SQL buffer (that is, a memory area). This SQL buffer is small and can only have one SQL statement, and the SQL statement that was originally in the buffer is overwritt
Dynamic SQL and oracle dynamic SQLDirectory
1. Pass values to dynamic statements (USING clause)
2. Retrieve values from dynamic statements (INTO clause)
3. Dynamic call stored
4. Pass the return value to the PL/SQL record type. The % rowtype variable is also available.
5. Pass and retrieve the value. INTO clause before the USING clause
6. multi-row query option.
limited to the shared cursor of the target SQL. That is, it allows Oracle to use hard parsing when executing the target SQL and remains the same as it did when all other SQL was executed.[emailprotected]>altersystemflushshared_pool; Systemaltered. [Emailprotected]>selectobj
ORACLE provides two types of SQL optimizer: CBO and RBO. CBO was introduced in ORACLE7, but it was only mature in ORACLE8i. ORACLE has explicitly stated thatIn later versions (ORACLE 10G), RBO will no longer be supported. Therefore, selecting CBO is an inevitable trend.
CBO and RBO, as different
analysis, dynamic SQL was executed in exchange for its flexibility in the loss of system performance. So it is necessary to optimize it to a certain extent, the author according to the actual development experience to give some development skills, it should be pointed out that many of the experience here is not limited to dynamic SQL, some also apply to static SQL
Before executing an SQL statement, Oracle needs to first check the SQL Execution Plan and then execute the SQL statement according to the execution plan. The optimizer is responsible for analyzing the execution plan, under different conditions, an SQL statement may have mult
, dept_name from Dept d Where exists (select 'x'From EMP e where E. dept_no = D. dept_no ); (19) SQL statements are written in uppercase. Because Oracle always parses SQL statements first, converts lowercase letters to uppercase and then executes them. (20) In Java Code Try to use the connector "+" to connect strings!
name', @ optvalue = nullGOEXEC master. dbo. sp_serveroption @ server = n' HZTMVQD ', @ optname = n' lazy schema validation', @ optvalue = n' false' GOEXEC master. dbo. sp_serveroption @ server = n' HZTMVQD ', @ optname = n' query timeout', @ optvalue = n' 0' GOEXEC master. dbo. sp_serveroption @ server = n' HZTMVQD ', @ optname = n' use remote collation', @ optvalue = n' true'
Note:
1. The data source must be written as ip + SID, for example, 172.2
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