Teradata tips
14. March 2009 18:01A database may contain :
Tables – contain data
Views – are previously defined “windows” to the data
Macros – are stored SQL statements
Triggers – are SQL statements associated with a table
Join indexes – are user defined pre-joins or pre-aggregations
Stored-procedures – are pre-written SQL scripts with defined procedural processing using Stored procedures control statements
Definition of default database:
.logon irena
Password: abc123
The normal default database for this logon is irena until:
* User logs off
* A new database control is used
The database command used to change default database
You can easily verify you current default database:
Select database
Other build-in function:
Current_date
Current_time
Current_timestamp
Date
Profile
Role
Time
Bteq – is a front end tool for submitting SQL queries. Bteq stands for basic Teradata Query programs
There are many tools available to provide help for the Teradata Sql user or programmer
* Help command
Provides information on a specified database object.
There are many objects for which help may be requested.
Databases and users
HELP DATABASE
HELP USER
Database Objects
HELP TABLE – shows the name, data type and comment of all columns
HELP VIEW
HELP MACRO
HELP COLUMN
HELP INDEX
HELP STATISTICS
HELP CONSTRAINT
HELP VOLATILE TABLE
HELP JOIN INDEX
HELP HESH INDEX
HELP TRIGGER
HELP PROCEDURE
HELP FUNCTION
* Show command
SHOW TABLE – shows the most current definition of the table
SHOW VIEW
SHOW JOINT INDEX
SHOW PROCEDURE
Shoes how an object was created, intended as a convenience to the developer
* Explain feature
Shoes how a query will execute in Teradata
It’s recommended to use Explain modifier before the SQL request – to see the plan execution of SQL. Explain function returns the plan how the optimizer will execute the SQL.
For example if you see that you request cause Full-table scan on a big table or cause Cartesian product join without intention – it’s preferable to rewrite request and write more efficient joint.
Explain provides:
* Translation of AMP steps
* A row count and time estimation for comparison only
* Which indexes if any will be used
* Whether individual steps will be used in parallel
Email 
11/5/2009 11:30:38 AM
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