Oracle

I. Introduction of the Platform environmentSystem: Win7 64-bitDevelopment tools: vs +oracle 11Project: ASP. NET Web ApplicationDeployment: IIS Local Application Mode　　Ii. Description of the problemThrow exception when opening database connection

There are two simple examples to illustrate the efficiency issues of "exists" and "in"1) SELECT * from T1 where exists (select 1 from T2 where t1.a=t2.a);When the T1 data volume is small and the T2 data is very large, the query efficiency of T12)

method One: by To_number function exception to judgeCREATE 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

Today, when we suddenly recall Oracle's paging query, most of the cases are used:SELECT * FROM(SELECT a.*, ROWNUM RNFrom (SELECT * from table_name) AWHERE ROWNUM )WHERE RN >= 21Said to be efficient, but for the SELECT * FROM table_name This original

The following SQL execution time is decremented by ordinal.1, dynamic SQL, no bound variables, each execution of a hard parse operation, occupy a large pool space, if the pool space is insufficient, the other SQL statements will cause the resolution

When you import/create an Oracle database table, sometimes we examine the discovery, import/create table, and the table space created is not the default table space we want. At this point we need to modify the user's default tablespace and then

- ---------------------Here is the query numeric field value/ *declarecursor cur_query is select table_name, column_ Name, data_type from User_tab_columns; a number; Sql_hard varchar2 (+); VV Number;begin for rec1 in Cur_query loop a:=0; If

1. An update and delete can kill a large chunk of people because everyone thinks this sentence is very well written, not just:Update table set a=x,b=y;Delete from table where name=xxOf course, now I talk about this problem, we certainly disagree, so

Oracle job creation, scheduled execution of tasksBeginSys.dbms_job.submit (Job = job,what = ' proc_test; ',Next_date = trunc (sysdate) +11/24,Interval = ' trunc (next_day (sysdate, ' Friday ')) +23/24 ');CoMMit;EndwhichJob: The system automatically

to put it simply, Oracle takes random numbers, mostly by calling Dbms_random packets, and there are roughly 4 ways to generate random numbers by Dbms_random packets: 1, Dbms_random.normalThis function does not take arguments, and is used to produce

Dynamic SQL (learning notes) and dynamic SQL learning notes Dynamic SQL Execute immediate dynamic SQL string [BUCK COLLECT] INTO custom variable, | record type USING [IN | OUT | in out] bound parameters] [RETURNING | RETURN] [bulk collect] INTO

Set Operations of data (learning notes) and computing learning notes A set operation is a binary operator. A total of four operators, and, difference, intersection, Cartesian Product Set operation Syntax:   Query statement [UNION | union all |

Conversion Function (learning notes), conversion function learning notes -- ****************************** Conversion Function-- Format the current date and time Select sysdate, to_char (SYSDATE, 'yyyy-MM-DD hh24: mi: ss') format date, to_char

General functions (learning notes), general function learning notes -- **************** Common functions-- NVL processing NULL-- NVL (number | column, default value). If the displayed number is NULL, the default value is used.-- NVL2 (number |

Database Connection (study notes) and Database Study Notes After Oracle is installed, several additional services will be added to the service. Since Oracle consumes system resources, we recommend that you change the service type to manual. You can

Oracle Performance Optimization Operation 14: using function-based indexes As mentioned above, any operations on columns may cause full table scanning. For example: select * from emp where substr (ename, 1, 2) = 'sm '; However, this type of

PLSQL _ performance optimization Series 1 _ concepts and importance of statistics (concepts) and plsql Performance Optimization 2014-12-18 Created By BaoXinjian I. Summary Statistic is very important to Oracle. It collects detailed information

Oralce time conversion usage TO_CHAR (DATE, FORMAT) 1. This week, this month, and this year -- This week select trunc (sysdate, 'D') + 1 from dual; -- Monday select trunc (sysdate, 'D') + 7 from dual; -- Sunday -- select trunc (sysdate, 'mm') from

Oracle Performance Optimization Operation 9: shielding useless Indexes Example of "oracle performance optimization operation 8" In actual queries, there are also queries involving DisposalCourseFlag = 6. If the index on this field is used, it is

Oracle Performance Optimization Operation 7: Index improves query efficiency when data distribution is uneven Index selection is low, but the data value distribution is very different, you can still use the index to improve efficiency. A. In