how to use dblink in oracle sql

Oracle SQL * plus is a client tool that interacts with oracle. In SQL * plus, you can run the SQL * plus command and the SQL * plus statement. The DML, DDL, and DCL statements we usually call are

PL/SQL enhancements in Oracle 12c Oracle 12c enhances a series of methods for defining and executing PL/SQL program units. This article covers several new features of Oracle 12c: 1. optimized the caller permission function for the result cache condition.2. PL/

Use awrextr. SQL to export awr raw data and awrextr. SQL to export awr1. Differences between original AWR data and AWR reports AWR raw data: The oracle Database mmon Process regularly dumps statistics from memory to disk and stores them in several tables in a structured manner to form an automatic workload storage ware

index.By default, Oracle only needs to navigate to the first row of index rows at the leftmost leaf block of the index by accessing the necessary branch blocks when doing an index full scan.Description: The result of the index full scan is also ordered, and is sorted by the index key Value column of the index, which means that the index full scan can be sortedeffect, while avoiding the real sort operation of the index key value Lieda.④: Index fast fu

After sqlserver2005, MSSQL began to use the recursive query method. Compare the methods for writing stored procedures or functions at the beginning. This method is simpler and more flexible. Oracle also has its own tree structure recursive query method, connect Next I will write a piece of SQL code by myself, and briefly comment out some usage of the CTE shar

Tags: des style io ar using SP for on fileI myself is a beginner of Oracle and SQL, some time ago saw Hanshunping Teacher's Oracle Video tutorial, feel very easy to learn, a lot of harvest. At the same time he also made a lot of notes, now want to put paper notes in their own words summed up. As the saying goes: teaching always complements each other, in the proc

guess: The SQL text in Oracle Ash report appears "* * SQL text not Available * *" for reasonsToday is doing HVR data synchronization software data synchronization test, due to the large amount of data (1 records 14M, contains LOB fields, 3,000 records) and the IO is poor, so the synchronization (to be exact, HVR refresh) is slow.During the HVR synchronization pro

data is returned as soon as possible)2. Execution method prompt:USE_NL (use nested loops to join)USE_MERGE (Union using merge join)USE_HASH (Union using hash join)3. Index prompt:INDEX (table index) (use the prompted table index for query)4. Other advanced prompts (such as parallel processing)The prompt function of ORACLE is a strong function and a complicated a

: = va_planguage ('java', 'c # ', 'c ++ ');FOR I IN 1 .. lang. COUNT LOOPDBMS_OUTPUT.PUT_LINE (lang (I ));End loop;END; 3) how to select the applicable collection type Generally, the first choice for the set type should be Associative array, because it does not require initialization or EXTEND operations and is the most efficient set type so far. The only drawback is that it can only be used for PL/SQL but not for databases. If you want to allow nega

described as follows, The data in the Oracle database is loaded to the DropDownList for the first time, In addition, you can select a user name in the DropDownList to obtain all information about the user, The function is very simple (because it is mainly used to access the Oracle database) Let's look at Code-Behind. The above is the Code-Behind part. In fact, apart from some different calling meth

is recommended for use with this select NO, listagg (EMP, ', ') within GROUP (ORDER by NULL) as Valsfrom onepiecegroupAbove we see the Listagg function syntax has over function, of course, our Listagg can also do analysis functionsSELECT NO, listagg (EMP, ', ') within GROUP (ORDER by NULL) through (partition by NO) from onepieceThe 3rd method of implementation has the To_string function, where the source code is as follows:CREATE OR REPLACE

Oracle SQL * plus is a client tool that interacts with oracle. In SQL * plus, you can run the SQL * plus command and the SQL * plus statement. The DML, DDL, and DCL statements we usually call are

SQL format execution sequence of oracle data structure and sequence number of SQL query processing, oraclesql I. execution sequence of SQL format FROM-> WHERE-> group by-> HAVING-> SELECT-> ORDER 1. The from clause assembles data from different data sources; 2. The where clause filters record rows based on specified c

[SQL] PL/SQL Syntax of Oracle and its extended data types summary PL/SQL syntax PL/SQL program consists of three parts: Declaration, execution, and exception handling. Template: [SQL] DECLARE/* variable Declaration */BEGIN/* Progr

Database engines with excellent design and performance can easily serve thousands of users at the same time. However, the database system of ldquo; underprovisioning rdquo; will greatly reduce its performance as more users access the system at the same time. In the worst case, the system may even crash. Of course, parallel access is the most important issue for any database solution. In order to solve the problem of parallel access, various database systems have proposed various solutions. Bot

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-set the ARRAYSIZE parameter in SQL * Plus, SQL * Forms, and Pro * C to increase the retrieval data v

Many students on the optimization of SQL seems to know very little, recently summed up the following 34 articles for reference only. (1) Select the most efficient table name order (valid only in the Rule-based optimizer): The Oracle parser processes the table names in the FROM clause in Right-to-left order, the last table (driving table), which is written in the FROM clause, is processed first, and in the

Tags: Tips control oracl Programmer Practice Union Multiple full table scans causeI. Use of the SQL language1. in operatorThe advantages of SQL in write are easier to write and easy to understand, which is more suitable for modern software development style.But SQL performance with in is always lower, and the steps tak

, Oracle converts ' * ' to all column names, which is done by querying the data dictionary, which means more time is spent (4) reduce the number of access to the database:Oracle has done a lot of work internally: Parsing SQL statements, estimating index utilization, binding variables, reading chunks, and so on; (5) in Sql*plus,

comparisons, including whitespace, character case), SQL does not need to be parsed (parsing) to be executed SQL, so try to maintain a uniform style of SQL.Error: Select E.emp_no from EMP E;Yes: SELECT e.emp_no from EMP e;1-2, the date format is clearIf you do not explicitly specify a time format, by default using the time format specified by the Nls_date_format parameter, you may not get the results you wa