The secondary index is an index type that helps to reduce the size of mapping by introducing another level of indexing. Hashing algorithm hashes the USI value i.e. So NUSI subtable is AMP local. Once you define Last_Name as a NUSI, Teradata will hash the Last_Name value and stores the row-id along with the index value in the subtable of same AMP. The participating AMPs access the base table rows, which are located on the same AMP as the NUSI subtable (in this case, one row from AMP 1 and two rows from AMP 2). Like Primary Indexes,Secondary Indexes also two Types (USI or NUSI). The UNIQUE option creates a USI which, perhaps redundantly, prevents the … A Secondary Index (SI) is an alternate data access path. As USI column contains only unique values, no duplicate value is there in any subtable i.e. However, it is possible that the subtable row and base table row could end up being stored on the same AMP, because both are hashed separately. Each participating AMP locates the row IDs (row hash value plus uniqueness value) of the base rows corresponding to the hash value (in this case, the base rows corresponding to hash value 567 are 640, 222, and 115). secondary indexes are used as another form of access to the data. As we know that we can define one and only one primary index for any specific table and accessing that table will be lightning fast only if we use primary index column(s) in  where clause. It is used to avoid the full table scan while accessing the data in the table. Real-time usage. Teradata will create subtable on each amp once you create the USI on a column or group of columns. Secondary Index that is created on Columns having Unique set of Values is called Unique Secondary Index. This is what is meant by AMP Local. Secondary Index is an index that is created on set of columns which are not in Primary Index and are helpful in faster retrieval of the rows from database. The reason to create a Single-Table Join Index is so joins can be performed faster because no Redistributions or Duplication needs to occur. Each AMP will hold the secondary index values for their rows in the base table only. Ideally you would use a Pi for most access as it is the most efficient but if you have additional columns that you use to access data from the table you might want to try a secondary index on column. Using hash map, it will find the amp number where the SI value is stored. Teradata provides A multicolumn NUSI that specifies an ORDER BY clause counts as 2 consecutive indexes in this calculation. The hashing algorithm calculates a row hash value (in this case, 602). 16.20 - Unique and Nonunique Secondary Indexes - Teradata Vantage NewSQL Engine Teradata Vantage™ SQL Fundamentals prodname Teradata Database Teradata Vantage NewSQL Engine vrm_release 16.20 created_date March 2019 category Programming Reference featnum B035-1141-162K. The AMPs whose subtables contain that value become the participating AMPs in this request (in this case, AMP1 and AMP2). 34. I believe that a great website is never truly finished.This website will become the launching point for many new features will be rolling out in both the near and distant future. Before proceeding with the Secondary Index, it is recommended to learn about Primary Index in Teradata. As soon as you define USI, Teradata will create subtable for Contact_no on each AMP. SQL Fundamentals, B035-1141 provides an overview of secondary indexes, while Database Design, B035-1094 provides more detail. PRIMARY INDEX nupi_tab1(col1,col2,col3) INDEX (col2); By Kishore_1 , 13 Sep 2011 | Tagged: unique secondary index violation | 7 comments Unlike Primary Index which can only be defined at the time of table creation, a Secondary Index can be create/drop after the creation of the table also. This is true for both the USI and the NUSI. 1999 − Largest database in the world using Teradata with 130 Terabytes. Now you have defined unique secondary index on the column Contact_No as below: CREATE UNIQUE INDEX (Contact_No) on Mydb.student; Teradata will perform below steps to maintain USI: In this way Teradata create and maintain subtable. Make sure you test each SI after you create them (and collect stats) to ensure they are being used. 1984 − Release of first database computer DBC/1012. Secondary Index that is created on Columns having Unique set of Values is called Unique Secondary Index. Roll_No column has been defined as Primary index. 1979 − Teradata was incorporated. Syntax: CREATE INDEX () ON table name; If we are having tbl_employee with one of the columns like department, then the secondary index can be defined for that column as below: So table will be distributed as per Roll_No across the AMP. Secondary index is an alternate path to the rows of a table in Teradata. PPI allows you to reduce the number of rows to be processed by using partition elimination. A. Each Amp now start to match the hash value in their student subtable. Creating a secondary index causes Teradata Database to build a separate internal subtable to contain the index rows, thus adding another set of rows that requires updating each time a table row is inserted, deleted, or updated. 022-45875 and generates hash value. First AMP is used to fetch the base row-id from the subtable and second amp is  for the actual value from the base table. You can drop and recreate secondary indexes dynamically, as they are needed.Secondary Indexes are stored in separate subtables that requires additional disk space and maintenance which is handled automatically by the system. We use cookies to ensure they are being used AMPs are activated to find the base table row resides hash. Other column in where clause often improve system performance index in Teradata table privilege on same! 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