The largest VARCHAR in Teradata is VARCHAR(64000). This defines a column that can store up to 64,000 characters of varying length.
Understanding VARCHAR in Teradata
VARCHAR, also known as CHARACTER VARYING, is a fundamental data type in Teradata used to store character string data of varying lengths. Unlike fixed-length CHAR columns, VARCHAR columns consume only the amount of storage required by the actual data entered, plus a small overhead for length information. This makes them efficient for storing text where the length can differ significantly from row to row.
Maximum Lengths for VARCHAR
While VARCHAR(64000) represents the absolute maximum current Teradata versions can support for a single column, the capacity can vary or be referred to by different aliases:
- VARCHAR(n): The
nspecifies the maximum number of characters the column can hold. The largest permissible value fornis64000. - CHARACTER VARYING(n): This is a direct synonym for
VARCHAR(n)and also supports a maximumnof64000. - LONG VARCHAR: This is an older, convenient alias for a large
VARCHARcolumn. Its actual maximum length depends on the specific Teradata version your server is running. It can be equivalent toVARCHAR(32000)orVARCHAR(64000).
Here's a summary of common VARCHAR maximums and aliases:
| Type/Alias | Maximum Length (Characters) | Notes |
|---|---|---|
VARCHAR(n) |
64,000 | n specifies the maximum length |
CHARACTER VARYING(n) |
64,000 | Functionally identical to VARCHAR(n) |
LONG VARCHAR |
32,000 or 64,000 | Alias; actual length depends on Teradata version |
Practical Considerations for Large VARCHARs
While Teradata offers robust support for large VARCHAR columns, it's essential to consider their impact on database design and performance:
- Storage Efficiency: While
VARCHARsaves space compared toCHARby only storing actual data, defining a very large maximum (e.g., 64,000) when not truly needed can still have implications. Teradata allocates space based on the defined maximum during certain operations, and it can impact memory usage when rows are processed. - Performance: Columns with extremely large character data can affect query performance, especially during operations like:
- Sorting: Sorting on very long string columns can be resource-intensive.
- Indexing: Creating indexes on large
VARCHARcolumns might not always be efficient or recommended for the entire column. - Data Transfer: Moving large textual data across the network or between systems can increase latency.
- Column Design: It's generally best practice to define the
VARCHARlength as precisely as possible, based on the maximum expected data length. Over-allocating significantly can lead to less efficient memory utilization within the database engine during processing, even if storage on disk is optimized. - Use Cases: Large
VARCHARcolumns are ideal for storing:- Long textual descriptions
- Comments or notes
- Small XML or JSON documents
- Unstructured data snippets
By understanding the capabilities and considerations, you can effectively utilize VARCHAR columns up to their maximum 64,000 character limit in your Teradata environment.
