Shantanu's Blog

Corporate Consultant

August 19, 2009

 

Adminer Interface

phpmyadmin is undoubtedly the best user interface for MySQL. But if you are looking for quick and dirty SQL interface, adminer is one the best!
It is lightweight but as powerful as it can get. It is just one .php file with NO configuration required.

wget -directory-prefix=/var/www/ -O adminer.php http://tinyurl.com/769ataj

Labels:


 

Using partitions as filters

There is an interesting "limit on limit" way to speed up the query ...

http://explainextended.com/2009/08/05/mysql-limit-on-limit/

And I just found out another practical way. Using partitions for data filtering!
I have used partitions only when there is a need to tame a huge table. But the alogrithum can also be used to speed up and simplify the complex queries. If you want to extract the data that belongs to 9 and 11 August, and process it further, why not to give this a try?

mysql> CREATE TABLE employees (separated DATETIME) PARTITION BY list (to_days(separated)) (
PARTITION p0 VALUES IN (to_days('2009-08-09')),
PARTITION p1 VALUES IN (to_days('2009-08-11'))
);

mysql> insert ignore into employees select * from t1;
Query OK, 172800 rows affected (0.92 sec)
Records: 1000000 Duplicates: 827200 Warnings: 0

Out of a million records, only 172,800 records were added to employees table those satisfied the date condition of being 9 or 11 August 09. We can now query our new table employees in order to speed up the joins and sorting.

The main disadvantage of this approach is that temporary tables can not be partitioned and therefore I can not use "create temporary table". If two threads try to work on the employees table then one of the threads will either fail or show wrong results. This trick can not be used in production, but is handy for admins.

Labels: ,


August 18, 2009

 

MySQL Case Study - 177

Grouping by Age Ranges (18-25,26-30,etc)

Hi all, I'm kind of stuck with a little problem. I know I can create PHP functions to create the results I want, but I was wondering if their is some unique way in mysql to accomplish this.

Basically here is my query to get a list of all the ages and a count of the number of employees for that age.

PHP Code:
SELECT FLOOR((TO_DAYS(NOW())-TO_DAYS(dob))/365.25) as Age,Count(db_id) as Count
FROM tbl_shareholder_list
WHERE current_employer = 'ASRC'
AND current_employee = 1
GROUP BY Age


What I'm trying to do is get a report that lumps a range of ages. So it comes out like

AgeRange --- Count
18-25 32
26-30 45
31-35 50

And so on and so on. Is there a trick to doing this or is it going to be a mess of IF statements and subqueries?

http://forums.devshed.com/mysql-help-4/grouping-by-age-ranges-18-25-26-30-etc-628617.html

Labels:


August 15, 2009

 

8 Regular Expressions You Should Know

Regular Expressions made easy!

Regular expressions are a language of their own. When you learn a new programming language, they're this little sub-language that makes no sense at first glance.



But with the graphical representation as above, the things become very clear.
I was looking for such an explanation for a very long time.

http://net.tutsplus.com/tutorials/other/8-regular-expressions-you-should-know/

Labels:


August 11, 2009

 

More examples of Sed and Awk

// select only "MainRecord" lines

$ cat awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

$ sed '/^$/q' awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

$ sed -n '/^$/q;p' awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

$ awk 'NF && $0 !~ /"Footer/' awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

$ awk '!NF { exit } 1' awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

$ awk ' NF {print} !NF {exit}' awktest.txt
MainRecord1 "115494",","FAELD","CT","
MainRecord2 "245774"," ,"","Gp"
MainRecord3 "165295","Aive","AHS","S",""
MainRecord4 "256254"," MOTOR "

_____

// to select record in the range of 00 to 04

$ cat awktest.txt
date 18:00:00
date 18:01:02
date 18:02:00
date 19:06:00
date 18:03:00
date 18:05:00

$ awk '{print $2}' | awk -F ":" '{if ($2<=4) print $0}' < awktest.txt
date 18:00:00
date 18:01:02
date 18:02:00
date 18:03:00

_____

$ cat file1.txt
abc|0|xyz
123|129|opq
def|0|678
890|pqw|sdf

// print record where second column has value of 0

$ awk -F'|' '$2=="0"' file1.txt
abc|0|xyz
def|0|678

_____

$ cat file1.txt
abc|0|xyz
123|129|opq
def|0|678
890|pqw|sdf

// replace the character 'a' with Apostrophe

$ sed -e "s/a/'/" file1.txt
'bc|0|xyz
123|129|opq
def|0|678
890|pqw|sdf

$ tr a "'" < file1.txt
'bc|0|xyz
123|129|opq
def|0|678
890|pqw|sdf

_____


$ cat infile.txt
|A|21|B1||1.1|
|A|21|C|RAGH|1.1|
|A|21|D1||1.1|
|A|21|C|YES|1.1

// replace blank cells with "NA"

$ awk 'BEGIN { FS="|"; OFS="|" } { if ($5=="") $5="NA"; print }' infile.txt
|A|21|B1|NA|1.1|
|A|21|C|RAGH|1.1|
|A|21|D1|NA|1.1|
|A|21|C|YES|1.1

$ awk -F"|" '$5 == "" {$5="NA"; print; next} {print}' OFS="|" infile.txt
|A|21|B1|NA|1.1|
|A|21|C|RAGH|1.1|
|A|21|D1|NA|1.1|
|A|21|C|YES|1.1

$ perl -ne '{s/(?<=\|)(?=\|)/NA/g;print;}' infile.txt
|A|21|B1|NA|1.1|
|A|21|C|RAGH|1.1|
|A|21|D1|NA|1.1|
|A|21|C|YES|1.1

Labels:


 

UNIX case study - 21

Counting and numbering Duplicates

How do I add a counter for the duplicate vlaues?

$ cat mysort.txt
yan
tar
tar
man
ban
tan
tub
tub
tub

$ awk '{print $1,word[$1]++}' mysort.txt
yan 0
tar 0
tar 1
man 0
ban 0
tan 0
tub 0
tub 1
tub 2

Labels:


 

UNIX case study - 20

Secondary sort


$ cat mysort.txt
004002004545454000001
041002004545222000002
006003008751525000003
007003008751352000004
006003008751142000005
004001005745745000006

$ sort -k 1,5 mysort.txt
004001005745745000006
004002004545454000001
006003008751142000005
006003008751525000003
007003008751352000004
041002004545222000002

I want to sort the file according to position 1-5 and secondary sort by the last position of file 16-21
the result should be like this (file2) :
004002004545454000001
004001005745745000006
006003008751525000003
006003008751142000005
007003008751352000004
041002004545222000002

http://www.unix.com/shell-programming-scripting/115911-sort-text-file.html

Ans:
sort -k 1.1,1.5 -k 1.16,1.21 mysort.txt

Labels:


 

UNIX case study - 19

Only printing certain rows

I mainly work with altering columns with awk but now I encountered a problem with dealing with rows.

So what I want to do is only print rows that start with a specific name. For example:

## joe jack john
ty1 3 4
ty1 5 6
ty2 4 7
tym 5 6
tyz 7 9

Basically what I want to do is get rid of the row with ## and tym and tyz. So I only want to print ty1, and ty2

So the output will look like this:

ty1 3 4
ty1 5 6
ty2 4 7

http://www.unix.com/shell-programming-scripting/116087-only-printing-certain-rows.html

Labels:


 

UNIX case study - 18

Changing the sequence number


I have a data as follow:

1 400
2 239
3 871
4 219
5 543
6 ...
7 ...
.. ...
.. ...
99 818
100 991

I want to replace the sequence number (column 1) that start from 150. The output should like this:

150 400
151 239
153 871
154 219
155 543
...
...

Can anyone tell me AWK code for this....

http://www.unix.com/shell-programming-scripting/116062-changing-sequence-number.html

Labels:


August 10, 2009

 

MySQL Case Study - 176

Use String to SELECT from Database


I have a string:
$string = "12,15,22";

Each of these values represents a usrID and I'd like to use these to select the rows associated with the $string.

Something like this:

SELECT usrFirst, usrLast FROM tblusers WHERE usrID = 12 OR 15 OR 22.

Now, the $string changes all the time, and sometimes can be a different number of ID's. Eg., sometimes 3, sometimes 4.

http://stackoverflow.com/questions/1225658/php-mysql-use-string-to-select-from-database

Labels:


 

MySQL Case Study - 175

Need REGEXP Matching in MySQL

I want to match a String which looks like this:

[lang_de]Hallo![/lang_de][lang_en]Hello![/lang_en]HeyHo[lang_es]Hola![/lang_es]

I want the matching to return true if there is text which is not enclosed by lang_tags (in this example: HeyHo). It could also be positioned at the beginning or end of the string.

Whitespace should NOT match, e.g. [lang_de]Tisch[/lang_de] [lang_en]Table[/lang_en] should not cause a match.

I can't use lookahead or lookback, because MySQL doesnt seem to support this.

Any Suggestions?

http://stackoverflow.com/questions/1224723/need-regexp-matching-in-mysql

Labels:


August 03, 2009

 

weekly group by

How do I select the Openning_price of the first day of each week?

SELECT t1 . * , WEEK( t1.tradingday ) wk
FROM daily_prices t1
LEFT
JOIN daily_prices t2 ON week( t1.tradingday ) = WEEK( t2.tradingday )
AND t1.tradingday > t2.tradingday
WHERE t2.securityid IS NULL ;

Pretty Interesting!

http://forums.mysql.com/read.php?10,273597,273638#msg-273638

Labels:


August 01, 2009

 

Rollback to MyISAM?

The following example shows that innodb tables are transaction safe and Atomic.
When I tried to insert 3, 4, 1 and 5 in a myisam table, it accepted 3 & 4 but failed on 1. We lost the last record, 5
In case of InnoDB, it rejected the entire statement and hence 3 & 4 were not added to the table.
Great.
But what happens when I kill / cancel the statement using Ctrl + C as I always do?
As per the bug 45309, even the InnoDB tables are partially populated just like MyISAM tables!

http://bugs.mysql.com/bug.php?id=45309

I guess unless you are using foreign keys, it is better to use the MyISAM tables.

_____

mysql> create table test_myisam (i int primary key) engine=myisam;
Query OK, 0 rows affected (0.19 sec)

mysql> create table test_innodb (i int primary key) engine=innodb;
Query OK, 0 rows affected (0.18 sec)

mysql> insert into test_myisam values (1),(2);
Query OK, 2 rows affected (0.19 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> insert into test_innodb values (1),(2);
Query OK, 2 rows affected (0.18 sec)
Records: 2 Duplicates: 0 Warnings: 0

mysql> insert into test_myisam values (3),(4),(1),(5);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql> select * from test_myisam;
+---+
| i |
+---+
| 1 |
| 2 |
| 3 |
| 4 |
+---+
4 rows in set (0.18 sec)

mysql> insert into test_innodb values (3),(4),(1),(5);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
mysql> select * from test_innodb;
+---+
| i |
+---+
| 1 |
| 2 |
+---+
2 rows in set (0.18 sec)

Labels:


 

Auto incremented primary key

Will the following statement work?

create table test_me (
id int auto_increment not null,
xx varchar(9),
key(id),
primary key (xx));

Contrary to my belief, id int not null auto_increment need not be a primary key!
I can declare it as a key and assign another column the primary status. I don't know where I will use this, but it helps knowing the possibilities. May be to avoid replication conflict.

Labels:


Archives

June 2001   July 2001   January 2003   May 2003   September 2003   October 2003   December 2003   January 2004   February 2004   March 2004   April 2004   May 2004   June 2004   July 2004   August 2004   September 2004   October 2004   November 2004   December 2004   January 2005   February 2005   March 2005   April 2005   May 2005   June 2005   July 2005   August 2005   September 2005   October 2005   November 2005   December 2005   January 2006   February 2006   March 2006   April 2006   May 2006   June 2006   July 2006   August 2006   September 2006   October 2006   November 2006   December 2006   January 2007   February 2007   March 2007   April 2007   June 2007   July 2007   August 2007   September 2007   October 2007   November 2007   December 2007   January 2008   February 2008   March 2008   April 2008   July 2008   August 2008   September 2008   October 2008   November 2008   December 2008   January 2009   February 2009   March 2009   April 2009   May 2009   June 2009   July 2009   August 2009   September 2009   October 2009   November 2009   December 2009   January 2010   February 2010   March 2010   April 2010   May 2010   June 2010   July 2010   August 2010   September 2010   October 2010   November 2010   December 2010   January 2011   February 2011   March 2011   April 2011   May 2011   June 2011   July 2011   August 2011   September 2011   October 2011   November 2011   December 2011   January 2012   February 2012   March 2012   April 2012   May 2012   June 2012   July 2012   August 2012   October 2012   November 2012   December 2012   January 2013   February 2013   March 2013   April 2013   May 2013   June 2013   July 2013   September 2013   October 2013   January 2014   March 2014   April 2014   May 2014   July 2014   August 2014   September 2014   October 2014   November 2014   December 2014   January 2015   February 2015   March 2015   April 2015   May 2015   June 2015   July 2015   August 2015   September 2015   January 2016   February 2016   March 2016   April 2016   May 2016   June 2016   July 2016   August 2016   September 2016   October 2016   November 2016   December 2016   January 2017   February 2017   April 2017   May 2017   June 2017   July 2017   August 2017   September 2017   October 2017   November 2017  

This page is powered by Blogger. Isn't yours?