Hi, iam learning MySql. Iam trieing to create a table in the database "guestbook"
at the command line in mysql heres what i type but i get a error
mysql>create table guestbook
->(
-> name varchar(40) null.
-> url varchar(40) null.
-> comments ... (3 Replies)
How do I write a perl script to get the cron jobs? I could do a
perl -e ' system "crontab -l > jobs.txt " ';
Is there a better way?
Then I can use perl to make changes to jobs.txt. How can I submit the changes.
I suppose I could use system "crontab jobs.txt", is there a better way?
... (0 Replies)
hi there, I am trying to create a stored procedure that i can pass the table name to and it will create a table with that name. but for some reason it creates with what i have defined as the variable name . In the case of the example below it creates a table called 'tname'
for example
... (6 Replies)
Hi pls help me out to short out this problem
rm PAB113_011.out
rm: PAB113_011.out: override protection 644 (yes/no)? n
If i give y it remove the file.
But i added the rm command as a part of ksh file and i tried to remove the file. Its not removing and the the file prompting as... (7 Replies)
how can i automatically create a file on Linux? like a process that searches for the file and if the file does not exist, it automatically makes the file (3 Replies)
I need to extract the data from oracle table and written the below code.
But it is not working.There is some problem with the query and output is shown is No rows selected" . If I run the same query from sql developer there is my required output.
And if I run the shell script with simple sql... (7 Replies)
I feel stupid for asking this because it seems that MYSQL code isn't working the way that I think it should work.
Basically I wrote code like this:
select * from `Test_DC_Trailer` HAVING max(DR_RefKey);
Where the DR_RefKey is a unique numeric field that is auto iterated (like a primary key)... (7 Replies)
Hi ,
I need to filter input file according to following
All rows with the following conditions should be removed
1) If in a row, the number of 'N's starting col 2 exceeds 2 (3 or more)
OR
2) If a row is duplicated with the same value, starting col 2,
A value 'N' is considered missing... (1 Reply)
Dear All,
I am trying to write a Unix Script which fires a sql query. The output of the sql query gives multiple rows. Each row should be saved in a separate Unix File.
The number of rows of sql output can be variable. I am able save all the rows in one file but in separate files.
Any... (14 Replies)
Hello
I've four fields . They are First Name, Last Name, Age, Country. So when I run a Unix command, I get below output with these fields comes every time in different order as you can see. Some times first name is the first row and other time last name is first row in the output and etc etc..... (9 Replies)
Discussion started by: rprpr
9 Replies
LEARN ABOUT REDHAT
cluster
CLUSTER(7) SQL Commands CLUSTER(7)NAME
CLUSTER - cluster a table according to an index
SYNOPSIS
CLUSTER indexname ON tablename
INPUTS
indexname
The name of an index.
table The name (possibly schema-qualified) of a table.
OUTPUTS
CLUSTER
The clustering was done successfully.
DESCRIPTION
CLUSTER instructs PostgreSQL to cluster the table specified by table based on the index specified by indexname. The index must already have
been defined on tablename.
When a table is clustered, it is physically reordered based on the index information. Clustering is a one-time operation: when the table is
subsequently updated, the changes are not clustered. That is, no attempt is made to store new or updated tuples according to their index
order. If one wishes, one can periodically re-cluster by issuing the command again.
NOTES
In cases where you are accessing single rows randomly within a table, the actual order of the data in the heap table is unimportant. How-
ever, if you tend to access some data more than others, and there is an index that groups them together, you will benefit from using CLUS-
TER.
Another place where CLUSTER is helpful is in cases where you use an index to pull out several rows from a table. If you are requesting a
range of indexed values from a table, or a single indexed value that has multiple rows that match, CLUSTER will help because once the index
identifies the heap page for the first row that matches, all other rows that match are probably already on the same heap page, saving disk
accesses and speeding up the query.
During the cluster operation, a temporary copy of the table is created that contains the table data in the index order. Temporary copies of
each index on the table are created as well. Therefore, you need free space on disk at least equal to the sum of the table size and the
index sizes.
CLUSTER preserves GRANT, inheritance, index, foreign key, and other ancillary information about the table.
Because the optimizer records statistics about the ordering of tables, it is advisable to run ANALYZE on the newly clustered table. Other-
wise, the optimizer may make poor choices of query plans.
There is another way to cluster data. The CLUSTER command reorders the original table using the ordering of the index you specify. This can
be slow on large tables because the rows are fetched from the heap in index order, and if the heap table is unordered, the entries are on
random pages, so there is one disk page retrieved for every row moved. (PostgreSQL has a cache, but the majority of a big table will not
fit in the cache.) The other way to cluster a table is to use
SELECT columnlist INTO TABLE newtable
FROM table ORDER BY columnlist
which uses the PostgreSQL sorting code in the ORDER BY clause to create the desired order; this is usually much faster than an index scan
for unordered data. You then drop the old table, use ALTER TABLE...RENAME to rename newtable to the old name, and recreate the table's
indexes. However, this approach does not preserve OIDs, constraints, foreign key relationships, granted privileges, and other ancillary
properties of the table --- all such items must be manually recreated.
USAGE
Cluster the employees relation on the basis of its ID attribute:
CLUSTER emp_ind ON emp;
COMPATIBILITY
SQL92
There is no CLUSTER statement in SQL92.
SQL - Language Statements 2002-11-22 CLUSTER(7)