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the rownum=2 results. Since rownum are all starting from 1, but more than 1 of the natural numbers in rownum do equal to the judgment is considered false condition, so can not find rownum = N (n>1 natural number).Sql> Select Rownum,id,name from student where rownum=1; (You can use a limit to return the number of records to ensure no errors, such as: implicit cursors)Sql> Select Rownum,id,name from student
the table (Sp_spaceuse)3. Upgrading hardware4, according to the query criteria, index, optimize the index, optimize access, limit the amount of data in the result set. Note the fill factor is appropriate (preferably using the default value of 0). The index should be as small as possible, using a Lie Jian index with a small number of bytes (refer to the creation of the index), do not Jianjian a single index on a5, improve speed;6, expand server memory
disk I/O, resulting in slow query. If the execution plan stability is not used, analyze both the table and index, which may directly increase the query speed. The analysis table command can use analyze table to analyze indexes. You can use the analyze Index Command. For tables with less than 1 million, you can analyze the entire table. For large tables, you can analyze them by percentage, but the percentag
-----------------------------------------------------------------Why? Chinese Input Test finds that the queried data is no longer normal because these Chinese characters are stored in the ZHS16GBK encoding format. However, after you query the data, convert it according to the Oracle Customer Service Code (UTF8, and converted to the UTF8 encoding format, but the operating system is simplified Chinese (GB2312
Tags: integer table can also be between output UI sha off row migration[ Oracle-based SQL Optimization ] Oracle-based SQL optimization "Bo Master" Gao Ruilin "Blog Address" http://www.cnblogs.com/grl214 A. Written Intent Description In the early stage of the system development, due to les
Management of 1.Oracle Tables Naming conventions for table and column names: Must start with a letter; Length cannot exceed 30 characters; Cannot use Oracle's reserved words; Use only the following characters: A-Z, A-Z, 0-9, $, # etc. Data types supported by Oracle: Character type Char fixed length maximum of 2000 characterschar (four)----' Little Han ' before the descr
consistency of the constraints of the record. 2. As of scn: We use the dbms_flashback.get_system_change_number function to obtain the current scn of oracle, and then execute the data modification operation. SQL> select dbms_flashback.get_system_change_number from dual;GET_SYSTEM_CHANGE_NUMBER------------------------14229608 Delete data: SQL
used to obtain DDL state information for any database object. For example, you can query the view's DDL information by replacing the first parameter with a ' view ' and the second by changing the name of the view.SELECT dbms_metadata.get_ddl (' TABLE ', ' table_name ', ' user_name ') from DUAL; Get current modeThis is another query statement that can get the name of the current pattern.SELECT sys_conte
statement is used to query the names of all tables owned by a user. (2) The buffer of sqlplus caches the last SQL statement. You can use "/" to execute the last SQL statement, or use the edit command to edit the last SQL statement. L command (list) (sqlplus command) can display the last command in buffer. The sqlplus
Tags: Oracle where generalSQL query statement describes the--select statement1. Simple SELECT query statement1.1 Check.Sql> select * from EMP;1.2 Check ListSql> select Empno,ename from emp;1.3 Related queriesSyntax for Oracle:Select a.*,b.* from emp a,dept b where a.deptno=b.deptno;General Syntax:Select a.*,b.* from emp a joins Dept b on (a.deptno = B.deptno);1.4
for language settings. If the character set is zhs16gbk, The nls_lang can be American_America.zhs16gbk. Involves three character sets, 1. Character Set on the El server side; 2. Character Set of oracle client; 3. dmp file character set. During data import, the three character sets must be consistent before the data can be correctly imported. 2.1 query character sets on
Basic query optimization and subquery Optimization in Oracle databases 1. Reasonably sort query Conditions Oracle uses the bottom-up sequence to parse WHERE data. From the perspective of performance optimization, we recommend that you write the conditions that can filter out a large number of record rows at the end of
: CREATE view v_row_col_notnull as select id, 'c1 'cn, c1 cv FROM t_col_row where c1 is not null union all select id, 'c2 'cn, c2 cv FROM t_col_row where c2 is not null union all select id, 'c3' cn, c3 cv FROM t_col_row where c3 is not null; 8. The following may be the oracle view frequently used by DBAs. 1. example: If hash_value: 3111103299 is known, query the SQL
. Currently, this parameter is not supported.And 17.3.2.1. rules and restrictions on using Stored Procedures To use stored procedures in hibernate, you must follow some rules. stored procedures that do not follow these rules will not be available. If you still want to use them, you mustSession. Connection ()These rules apply to different databases because database providers have different stored procedure syntax and semantics. Query of stored proce
cannot create a database structure.Connect: A user with connect permission can only log on to Oracle, not create an entity, and cannot create a database structure.For normal users: Grant Connect, resource permissions.For DBA administration users: Grant Connect,resource, dba authority.System Permission Authorization command:System permissions can only be granted by the DBA User: sys, system (only two users at the beginning)Authorization Command:sql> G
; = 11; 10 rows have been selected. Execution Plan----------------------------------------------------------0 SELECT statement optimizer = choose (cost = 43 card = 20 bytes = 1840)1 0 view (cost = 43 card = 20 bytes = 1840)2 1 count (stopkey)3 2 view (cost = 43 card = 6361 bytes = 502519)4 3 sort (order by stopkey) (cost = 43 card = 6361 bytes = 133581)5 4 Table Access (full) of 'T' (cost = 9 card = 6361 bytes = 133581) Statistics----------------------------------------------------------
and 123456 passwordC:\>sqlplus scott/123456Exit Sqlplus Environmentsql:\>exit;Query all tables under the Scott userSELECT * from tab;Query who the current user isShow user;Set the displayed column width (character, date), 10 characters wide, a for the character typeCol ename for A12;A12: Indicates a display width of 12 characters, a case insensitiveExecutes the most recent
to improve the efficiency of SQL query how to write the precedence of where statement conditionshttp://blog.csdn.net/sforiz/article/details/5345359We have to do not only write SQL, but also to write good performance of SQL statements.(1) Select the most efficient table name order (valid only in the rule-based optimizer
Statement 8: place the where condition in Statement 7 after the on clause. Select o. id, o. order_number, o. customer_id, c. id, c. name From orders o left outer join MERs c on c. id = o. customer_id and o. order_number The query results of statement 7 and statement 8 are obviously different, and the results displayed in Statement 8 are hard to understand. Therefore, when writing a join query, we recomme
Tags: style io ar using SP for data on art1.string Contact operatorSQL Server use + or contact (SQL Server 2012)In Oracle, you can also use the contact, but can not used + to the contact string, you should use | |;2.oracle date time is different with SQL Server date.SQL Server Date just has a date part, not contains ti
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