What is the use of join index in Teradata?
JOIN INDEX is a materialized view. Its definition is permanently stored and the data is updated whenever the base tables referred in the join index is updated. JOIN INDEX may contain one or more tables and also contain pre-aggregated data. Join indexes are mainly used for improving the performance.
What are the limitations of a primary index?
Disadvantages of Indexing Important drawbacks/cons of Indexing are: To perform the indexing database management system, you need a primary key on the table with a unique value. You can’t perform any other indexes in Database on the Indexed data. You are not allowed to partition an index-organized table.
What is a disadvantage of indexing?
There is some overhead to an index. The index itself occupies space on disk and memory (when used). So, if space or memory are issues then too many indexes could be a problem. When data is inserted/updated/deleted, then the index needs to be maintained as well as the original data.
When should indexes not be used?
Indexes should not be used on tables containing few records. Tables that have frequent, large batch updates or insert operations. Indexes should not be used on columns that contain a high number of NULL values. Indexes should not be used on the columns that are frequently manipulated.
What is Multi value compression?
Multivalue compression (MVC) compresses repeating values in a column when you specify the value in a compression list in the column definition.
What do you need to know about Teradata join index?
Teradata – JOIN Index 1 Single Table Join Index. Single Table Join index allows to partition a large table based on the different primary index columns than the one from the base table. 2 Multi Table Join Index. A multi-table join index is created by joining more than one table. 3 Aggregate Join Index.
When to use a single table join index?
A single table join index is used to create indexing structure for a single table but with different primary index. This improves the performance of joins as no distribution or duplication is needed. The user will query on the base table, but PE will decide whether to access base table or single table join index.
How are Join indexes similar to materialized views?
Join indexes are comparable to materialized views. Although the name indicates that join indexes are an index structure, they have to be considered more as an added layer of pre-joined, pre-aggregated or permanent tables with its own Primary Index, Secondary Indexes, and row-level partitioning.
How to hash a column combination in Teradata?
Teradata can hash this column combination in order to identify the AMP containing a row. Again, the rowids are used to access the base table. A message with the rowid is sent to the AMP in order to receive the required row. (2b) There is a USI on the base table available which matches the column set of the NUPI.