Oracle

I. Defining what a subquery is When a query is a condition of another query, it is called a subqueryYou can add a subquery anywhere in the SQL. two. When to use subqueries Use it when the problem cannot be solved in one step. For example: query

1. Choose the appropriate Oracle optimizer There are 3 Oracle optimizer types: A. Rule (rule-based) B. Cost (based on costs) C. CHOOSE (optional) Set the default optimizer to pass various declarations of optimizer_mode parameters in the Init.ora

This is often the case when you use Pl/sql developer to remove users."Unable to delete the currently connected user" Workaround I post the SQL statement directly /* Delete the current connection user * *- 1, first switch to SYSTEM user

☆ Database----containers for storing dataThe primary function of a database is to save data.The storage structure of the database---how the data is stored in the database The storage structure of the ☆oracle database:Logical storage structure: How

1 utl_file_dir parameter definition Utl_file_dir is a "static parameter" in Oracle, and you can set one or more paths. Specifies the path for file I/O operations in Pl/sql (which can be utl_file packages). Utl_file_dir is a "static parameter" in

Problem: VARCHAR2 (4000) ABC; Intert into table_name (ABC) VALUES (' Here are 1500 characters ... '); Error: Insert character too long. After testing, found that a Chinese character accounted for 3 bytes, it will be an error. The crux of the problem:

--Start In the database, each row has an address, and we can query the pseudo-column ROWID to get this value. CREATE TABLE TEST ( NAME VARCHAR) ; INSERT into TEST VALUES (' test '); SELECT ROWID, NAME from TEST; --Results ROWID NAME

This example implements the connection string and removes the duplicate item. An aggregate function is actually an object:[SQL] View Plain Copy create or replace type distinct_concat_type as object   (   --Object variable      cat_string varchar2 (+

--Start First, we prepare the test data. CREATE TABLE TEST ( NAME VARCHAR2, birthday DATE ); INSERT into TEST VALUES (' John ', DATE ' 2014-12-14 '); INSERT into TEST VALUES (' Dick ', DATE ' 2013-12-14 '); INSERT into TEST VALUES (' Harry ',

Import Export using Exp/imp Before starting Exp/imp, there are several points to note: 1 This section takes Oracle 10g for example. 2 Exp, IMP is the next executable file of the operating system, stored in the/oracle_home/bin directory. So between

Method One: To judge by To_number function anomaly CREATE OR REPLACE FUNCTION is_number (Str_ VARCHAR2) return VARCHAR2IsNUM_ number;BEGINNum_: = To_number (STR_);Return ' Y ';EXCEPTIONWhen others THENReturn ' N ';End Is_number;/ Sql> Select

L Transfer from: http://www.cnblogs.com/lovemoon714/archive/2012/03/02/2376782.html 1. Overview 1.1, all join connection, can add like where a.id= ' 1000 ' condition, achieve the same effect. 1.2, in addition to the cross join can not add on, other

Table structure: Name Subject Score John Language 89 John Math 73 Dick Language 73 Dick Math 73 Required Format: Name Subject Score John Language = 89, digital =73 Dick language = 73, digital =73 Query statement: Select Name, Wm_concat (to_char) (

Directory===============================================1. The arrangement with null value2.top/bottom N Query3.first/last ranking Query4. Query by LevelOne, with a null value of the arrangement:In the previous article on Oracle development topics:

--Create a temporary tableCREATE TABLE Tj_org_new(Deptcode NVARCHAR2 (255),Orgdesc NVARCHAR2 (255),Organtype NVARCHAR2 (255),Levelfact Number (6),Parentdeptcode NVARCHAR2 (255))Tablespace TESTPctfree 10Initrans 1Maxtrans 255Storage(Initial

Problem Description: Use Oracle's multiple page query statement, data duplication between different pages, but the database data is correct, query all the time can also be displayed. SQL instance: Select RowNum rn,ta.* from (select a.*,b.* to

Manually start an ORACLE database instance assume that the instance name ORCL first export the environment variable in the configuration file or set ORACLE_SID=ORCL sqlplus Sys/password as Sysdba sql>startup; The startup command reads the

1. Database Configuration First of all, your installation database, which is installed here is Oracle, does not explain. Open the Web-inf/config/systemglobals.properties file, locate the configuration parameters database.driver.name and configure

Query and delete duplicate records SQL statement 1, find redundant records in the table, duplicate records are based on a single field (ID) to determine select * from table where Id in (select Id from table group Byid having count (ID) > 1) 2,

Oracle redo logs Oracle 's database log is called Redo log, and all data changes are recorded redo log, which can be used to repair a damaged database. The redo log is grouped, and the default is three groups. Redo Log is used in turn, a redo log