An universal algorithm design of fixed length substring locating
Stringlocating is a very common operation not only in the SQL design but also in theclient development tools, in which functions are also supplied to realize thelocating operation, such as the ‘LOCATE’ function in DB2 or ‘POS function in DELPHI.
In fact, we maymeet with the special string locating, such as, we have to locate fixed lengthstring locating, in which you may get the wrong result if you use the given ‘LOCATEor ‘POS function. In the essay, I give an algorithm that you can easily transformto other DBMS or client development tools.
There is a fewtables inn the OLTP in my company which contain some fixed coded fields, suchas field ‘roadcomb’ recording all the highways that vehicles have passed by.Each highway is coded in two hex characters, and 17 means highway between Canton and Huizhou.
In one task, Istart to statistic the records in a certain time that passed through Guanghuihighway. So the solution SQL is in the bellow. As for how to create and executea DB2 function please see my essay How to createDB2 user function easily by DB Query Analyzer 6.03
SELECT *
FROMDEVELOP.TB_OUTLISTGW
WHERE LOCATE(ROADCOMB,’11’)>0
FETCH FIRST 100ROW ONLY
WITH UR;
However, it willresult some errors. What will happen if one value of ‘ROADCOMB’ is '01100110011001100110011001100110'.According the SQL above, it is a legal record which will return. In fact, thevehicle has never passed through Guanghui highway. As a result, the propermethod is locate the field every two characters, not one character. So I designa function in the bellow and I will execute them by DB Query Analyzer.
DROP FUNCTIONDEVELOP.F_LOCATE_FIXED
$$
CREATE FUNCTIONDEVELOP.F_LOCATE_FIXED(IN V_SRC VARCHAR(4096),IN V_DES VARCHAR(4096))
RETURNS INTEGER
LANGUAGE SQL
DETERMINISTIC
NO EXTERNALACTION
CONTAINS SQL
BEGIN ATOMIC
DECLARE v_result INTEGER DEFAULT 0;
DECLARE str_road VARCHAR(4096);
DECLARE v_len_src INTEGER;
DECLARE v_len_des INTEGER;
DECLARE v_pos_src INTEGER DEFAULT 1;
SET v_len_des=LENGTH(TRIM(V_DES));
SET v_len_src=LENGTH(TRIM(V_SRC));
SET v_result=0;
AUTHLOOP:
WHILE v_pos_src+v_len_src<=v_len_des DO
SET str_road=SUBSTR(V_DES,v_pos_src,v_len_src);
IF ( str_road=V_SRC ) THEN
SET v_result=v_pos_src; --return the physical position
SET v_result=v_result/v_len_src+1; -- return the logical position, if not be annotated.
LEAVE AUTHLOOP;
ELSE
SET v_pos_src=v_pos_src+v_len_src;
END IF;
END WHILE;
RETURN v_result;
END
$$
values DEVELOP.F_LOCATE_FIXED('11','4F0A0B0D231154533F01')
$$
values DEVELOP.F_LOCATE_FIXED('11','01100110011001100110011001100110')
$$
SELECT *
FROMDEVELOP.TB_OUTLISTGW
WHERE DEVELOP. F_LOCATE_FIXED ('11',ROADCOMB)>0
FETCH FIRST 100ROW ONLY
WITH UR;
$$
1 How to create the function in DB2 by DB QueryAnalzyer
Figure 1 SQL scripts to create the function and execute the function
Figure 2 SQl scripts are executed
Figure 3 DEVELOP.F_LOCATE_FIXED('11','4F0A0B0D231154533F01') returns 6
Figure 4
DEVELOP.F_LOCATE_FIXED('11','01100110011001100110011001100110') returns 0
When looking for ‘11’ in '01100110011001100110011001100110',Unlike ‘LOCATE’function in DB2, DEVELOP.F_LOCATE_FIXED return 0, the right result, which showsthat the vehicle has never passed through Guanghui highway.
A kind reminder, it is necessary to design your own function when notjust seeking the first position in the string, and it is likely to concern theloop operation.
Finally, I will give you a complex question. How to get all the vehicles fromtableTB_OUTLISTGW which passed from the given start toll station in thecertain highway to the give end toll station in the certain highway? The highways thatvehicles passed by are stored in field ROADCOMB, in tollstations are stored in the field ROADSSTARTSTATION and the out tollstations are stored in the field ROADESTARTSTATION in table TB_OUTLISTGW. Both ROADSSTARTSTATIONand ROADESTARTSTATION are coded in four-character-length hex string.
2 Brief introduction of DB Query Analzyer
DB Query Analyzeris presented by Master Genfeng, Ma from Chinese Mainland. It has Englishversion named ‘DB Query Analyzer’ and Simplified Chinese versionnamed 
DB Query Analyzeris one of the few excellent Client Tools in the world for its’ powerfulfunction, friendly interface, easy operation and applicability to everyproduction of RDBMS.
① It lets you query ODBC data sources, author SQLscripts and queries, return query results to a grid or free-form text or afile, retrieve ODBC driver information, ② execute multiple SQL scripts or stored procedures simultaneously,③save the result to files withhigh efficiency which is as quick as tools provided by database system. ④What is more, from 6.01, DBQuery Analyzer provides SQL Execute Schedule function to execute SQL scripts incertain time. If you select the option ‘SQL Schedule Reconnect’ in windowconfigurations, the Schedule SQL scripts will be executed as long as theDatabase Server is in use, even though the Database Server had been down. ⑤From version 6.03, withoutchanging any Windows OS settings or configurations, DB Query Analyzer can runon any Microsoft Windows OS directly such as Windows 10, Windows 8, Windows 7,Windows Vista, Windows 2003, Windows XP, Windows 2000, Windows NT, Windows ME,Windows 9X.
In the New products& Tools reviews of programmer second issue of 2007, DB Query Analyzer hadbeen strongly recommended.
DB Query Analyzeris one of the few excellent Client Tools in the world for its’ powerfulfunction, friendly interface, easy operation and applicability to everyproduction of RDBMS.
It lets you queryODBC data sources, author SQL scripts and queries, return query results to agrid or free-form text or a file, retrieve ODBC driver information, executemultiple SQL scripts or stored procedures simultaneously, save the result tofiles with high efficiency which is as quick as tools provided by databasesystem. What is more, from 6.01, DB Query Analyzer provides SQL ExecuteSchedule function to execute SQL scripts in certain time. If you select theoption ‘SQL Schedule Reconnect’ in window configurations, the Schedule SQLscripts will be executed as long as the Database Server is in use, even thoughthe Database Server had been down.
In the New products& Tools reviews of programmer second issue of 2007, DB Query Analyzer hadbeen strongly recommended.
Now the SimplifiedChinese version of DB Query Analyzer is the top 50 database applicationsoftware in the famous software website http://xiazai.zol.com.cn/download_order/sub_550.html .In most case it lies the top 10 and it has been downloaded more than 110,000 times.
82 technicalarticles about DB Query Analyzer have been published or been publishing incomputer journal, BAIDU Library, the CSDN resource or my four blog-websites.
DB Query Analyzer 6.04 download URL:
http://xiazai.zol.com.cn/detail/43/420901.shtml
http://www.unitedpowersoft.com/UpFile/DBQueryAnalyzer_English_604.rar
My blog are http://blog.csdn.net/magenfeng
http://blog.sina.com.cn/magenfeng
http://user.qzone.qq.com/630414817
Interview with CSDN: http://www.csdn.net/article/2014-08-09/2821124
82 technicalarticles about DB Query Analyzer have been published or been publishing incomputer journal, Baidu Library, the CSDN resource or my four blog-websites.
The following 7articles have been published in computer journals.
Guangdong Highway settlement business analysis systembased on Star Schema in Data Warehousing according to national standardization in Computer Era 7th issue of 2015 in Hangzhou.
DBQuery Analyzer to cancel a running SQL statement in Computer Era 12th issue of 2011 in Hangzhou.
DBQuery Analyzer Returns Information in More Detail While Batch SQL Statement Endof Execution in Computer Programming Skill & Maintenance 24th issue of 2011 in Beijing
TheApplication of the Transactions Control in DB2 with DB Query Analyzer inComputer Programming Skill & Maintenance 22nd issue of 2011 in Beijing.
Howdoes DB Query Analyzer cancel the SQL statement committed to DBMS in ComputerEngineering & Software 6th issue of 2011 in Tianjin.
TheApplication of the Transactions Control in Oracle with DB Query Analyzer inMicrocomputer Applications11th issue of 2011 in Shanghai.
DB Query Analyzer had been stronglyrecommended In the New products & Tools reviews of programmer 2nd issue of2007.
The following 75 articleshave been published or been publishing in Baidu Library, the CSDN resource ormy four blog-websites.
TheDBMS that DB Query Analyzer Users often use cover all kinds of DBMS have beenpublished.
Howto configure ODBC DSN in Client to access remote DB2 for Windows
How to configure ODBC DSN to access localDB2 for Windows
WhichSQL statement is the trump card to the senior software developer
Exepacker prevent DB Query Analyzer from beging debugged have been published.
16articles from The 1st tip of DB Query Analyze to The 16th skills of DB QueryAnalyzer have been published.
Thetable name must be enclosed in double quotation marks or sqare bracket whileaccessing EXCEL by DB Query Analyzer
How to download the installation packageby ZOL Downer
DBQuery Analyzer, the most excellent Universal database Access tools on anyMicrosoft Windows OS
Demonstrationof DB Query Analyzer 6.03 Installation and Running on Microsoft Windows 8
Installand run DB Query Analyzer 6.04 on Microsoft Windows 10
Anuniversal algorithm design of locating fixed length string
