Teradata Reference
Thursday, November 1, 2012
Teradata interview questions
How to extract numbers from strings in Teradata Sql?
how can we analyze the locks ?
If the script is aborted. why it is aborted and how can you identify ?
how do you handle ET and UV errors ?
If the query is NOT WRITTEN PROPERLY then what are the recommendations you can give to the developer ?
If RDBMS is halted what will you do ?
we have the num like this +91666666666......i want to remove 91 and i want lo load remaining data to the target table..
whinch function we can use in teradata?
what is meant by Hot amp?
What is meant by MATCHTAG in multiload utility?
Cursors in Teradata - simple example
/* Program to Revise the employees salaries and return count based on range for a particular department */
Create procedure emp_sal(IN deptno INTEGER,OUT vrow INTEGER)
Begin
Declare v_cur CURSOR FOR select empno,salary from emp where deptno=:deptno;
DEclare v_empno INTEGER;
Declare v_sal INTEGER;
Declare V_count INTEGER default 0;
Declare V_rowcount INTEGER;
Declare V_pcount INTEGER;
OPEN v_cur;
set v_rowcount=ACTIVITY_COUNT;
set v_pcount=v_rowcount;
Repeat
FETCH v_CUR into v_empno,v_sal;
set v_count =v_count+1;
if(v_sal<30000) then
set Rev_sal=v_sal+v_sal*10/100;
elseif
if(v_sal<50000) then
set Rev_sal=v_sal+v_sal*8/100;
else
set Rev_sal=v_sal+v_sal*5/100;
end if;
// to insert into other table
select current_date;
INSERT rev_emp_sal(v_empno,v_sal,rev_sal,:current_date);
// update the employee table
Update emp set sal=rev_sal where empno=v_empno;
v_pcount=v_pcount-1;
unit v_pcount=0;
set vrow=v_count;
close cur1;
end;
Tuesday, October 23, 2012
Teradata - Performace Tuning
Use group by instead of distinct because distinct occupies more spool space
Use EXISTS instead of IN because EXISTS stops the process once it finds the value
Join Columns of same datatype
Use UNION ALL instead of UNION
Remove secondary indexes when the data is being loaded,updated or deleted
Avoid correlated queries,cross join, product join
use Delete ALL - normal delete have rollback, for delete all there is no rollback(no transient journal overhead)
Use EXISTS instead of IN because EXISTS stops the process once it finds the value
Join Columns of same datatype
Use UNION ALL instead of UNION
Remove secondary indexes when the data is being loaded,updated or deleted
Avoid correlated queries,cross join, product join
use Delete ALL - normal delete have rollback, for delete all there is no rollback(no transient journal overhead)
Does SDLC changes when you use Teradata instead of Oracle ?
If Teradata is just a database then no change
IF we are using utilities then it changes
If the schema is in 3rd normal form then there won't be huge changes
Teradata vs Other RDBMS
Teradata: Shared nothing(Ex: Each VPROC is associated with one VDisk)
Other: Shared Everything
Process Million of Instructions per second
Process Thousands of Instructions per second
Stores billions of rows
stores millions of rows
unconditional parallelism(Each AMP works with its own drive)
Conditional Parallelism
Better storage and fast retrieval(using indexes)
fast retrieval only
bulk load utilities(BTEQ,FLOAD,MLOAD,TPUMP)
limited utilities
Other: Shared Everything
Process Million of Instructions per second
Process Thousands of Instructions per second
Stores billions of rows
stores millions of rows
unconditional parallelism(Each AMP works with its own drive)
Conditional Parallelism
Better storage and fast retrieval(using indexes)
fast retrieval only
bulk load utilities(BTEQ,FLOAD,MLOAD,TPUMP)
limited utilities
Teradata Questions - SQL Queries
Number of nodes in a system
select count(distinct(nodeid)) from dbc.resusagescpu
To find database size
select sum(currentPerm) from DBC.diskspace where databasename='mydb'
To find table size
select sum(currentperm) from DBC.tablesize where databasename='mydb' and tablename='mytable'
To find version of terdata
select * from dbc.dbcinfo
To find CPU time consumed
select username,accountname,sum(CPUTIME) from dbc.ampusage where username='xyz' group by 1,2
To find the space used by each table in MB's in a database
select tablename,sum(currentperm)/1024/1024 MB
from DBC.AllSpace
where databasename='mydb'
group by 1
To identify skewness
SELECT
DatabaseName,
TableName,
SUM(CurrentPerm) AS CurrentPerm ,
SUM(PeakPerm) AS PeakPerm,
(100 - (AVG(CurrentPerm)/MAX(CurrentPerm)*100)) AS SkewFactor
FROM DBC.TableSize
WHERE databasename = database
AND TableName IN ('SALES' , 'CUSTOMERS')
GROUP BY 1,2
ORDER BY SkewFactor DESC;
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