Oracle

This articleArticleI saw it in a book, added my understanding, and shared it with everyone... Oracle scans tables in two ways: A. Full table scan. In this way, Oracle scans data from the first record of the table in order. B. rowid is used.

Sometimes a column is compared with a series of values. The simplest way is to use subqueries in the where clause. In the WHERE clause, you can use subqueries in two formats. 1. Use the in Operator 2. Use the exist Operator The first format is

Create test tables, which are frequently used by DBAs. Generally, they are created based on dba_objects. This article is based on the big_table of Master Tom for your reference. 1. big_table based on Oracle 10 GB --===================================

Reasonable creation of strategic indexes for database tables can greatly improve query performance. But in fact, the index we create in daily life is not a strategic index. It is precisely because a large number of redundant or useless indexes

Clustering factor is one of the parameters used to calculate cost in the CBO optimizer mode in Oracle statistics. It determines whether the current SQL statement is indexed, or full table scan and nested External table connection. In this case, what

Like rownum, rowid is a pseudo column, which is a non-user-defined column and is actually stored in the database. Each table has a rowid column, and a rowid value is usedUniquely identifies a record in a database table. Therefore, using rowid to

In a CBO optimizer-based environment, the generation of SQL Execution plans depends on the authenticity and completeness of statistical information. Such as column discretization, column histogram, index availability, clustering factor on the index.

Oracle 11g RAC installation, the first node to execute root. Sh encountered a CRS-0184/PRCR-1070, Google a lot of posts have not found a solution. Hey, let's calm down and look at the log !! The conclusion is a casual problem, as described below.   1

Migrate database from single instance to Oracle RAC # Preparation before restore# Backup database# Check listener# Check ASM disk group free space is sufficient.# The following steps was completed sucessful on Oracle 10g RAC + SuSE Linux

1. subprograms are named PL/SQL statement blocks, including stored procedures and functions, and their advantages (modular, reusable, and maintainability security ).2. Stored Procedure: create [or replace] procedure_name(argument1 [mode1]

Today I encountered a problem: Code: select row_no, roleid, roleName from (select roleid, roleName, rank() over(order by sum(decode(roundrs, 1, 40, 2, 20, 3, -10, 0, 20, 0)) + 50 desc, sum(decode(roundrs, 1, 1, 0)) desc,

Cause/trigger factor It is confirmed that "failed_login_attempts = 10 times" is set in the default profile in oracle11g by default. This problem occurs when the number of incorrect passwords reaches the set value. Impact and risk After the account

Cause/trigger factor This is because "password_life_time = 180 days" is set in the default profile in oracle11g by default. Impact and risk After the password expires, the business process has an exception connecting to the database, affecting

Similarities and differences between truncate, delete, and dropSame: truncate, delete without WHERE clause, and drop both delete table data.Differences:1. truncate and delete: delete only data. Do not delete the table structure (Definition)The drop

This problem is generally caused by data file loss or damage. You can perform the following steps: 1. Go to CMD and run set oracle_sid = fbms to ensure the correct Sid is connected; 2. Run sqlplus "/As sysdba"SQL> shutdown immediateSQL> startup

1. Data Definition Language (DDL): these commands are mainly used by database administrators to create and delete database entities. For example: Create, alter, drop, and so on; 2. data manipulation language (DML): data manipulation language inserts

1. Obtain the values of 6th to 10th records in the table.1.1 Method 1: Use the minus statementAssume that the DDL statement is as follows: The following is a reference clip: CREATE TABLE T(ID VARCHAR2(4） PRIMARY KEY， VALUE INT) The first method

Create Table Table1 (ID varchar2 (10) Not null, grzhye number (10, 2), gmsfhm varchar2 (18), rylb varchar2 (10), cardno varchar2 (20 )); comment on column table1.id is 'personal number'; Comment on column table1.grzhye is 'personal account balance ';

Hierarchical query Concept Syntax format: Select [level], column, expr... from table [Where condition] Start with Condition Connect by [prior column1 = column2 | Column1 = prior column2]; Hierarchical query is identified by the start with and

I always think that my Oracle notes are especially spam, but I can't tell you how to write them. I 'd like to thank you for your suggestion! There are two types of SQL functions: single-row function and multi-row function single-row function: the