What happens to the underlying table data when a CLUSTER BY clause is added to a Snowflake table?
When aCLUSTER BYclause is added to a Snowflake table, it specifies one or more columns to organize the data within the table's micro-partitions. This clustering aims to colocate data with similar values in the same or adjacent micro-partitions. By doing so, it enhances the efficiency of query pruning, where the Snowflake query optimizer can skip over irrelevant micro-partitions that do not contain the data relevant to the query, thereby improving performance.
References:
Snowflake Documentation on Clustering Keys & Clustered Tables1.
Community discussions on how source data's ordering affects a table with a cluster key
Which Snowflake feature or tool helps troubleshoot issues in SQL query expressions that commonly cause performance bottlenecks?
The Snowflake feature that helps troubleshoot issues in SQL query expressions and commonly identify performance bottlenecks is the Query Profile. The Query Profile provides a detailed breakdown of a query's execution plan, including each operation's time and resources consumed. It visualizes the steps involved in the query execution, highlighting areas that may be causing inefficiencies, such as full table scans, large joins, or operations that could benefit from optimization.
By examining the Query Profile, developers and database administrators can identify and troubleshoot performance issues, optimize query structures, and make informed decisions about potential schema or indexing changes to improve performance.
References:
Snowflake Documentation on Query Profile: Using the Query Profile
A user wants to access files stored in a stage without authenticating into Snowflake. Which type of URL should be used?
References:[COF-C02] SnowPro Core Certification Exam Study Guide
When unloading data, which combination of parameters should be used to differentiate between empty strings and NULL values? (Select TWO).
When unloading data in Snowflake, it is essential to differentiate between empty strings and NULL values to preserve data integrity. The parameters FIELD_OPTIONALLY_ENCLOSED_BY and EMPTY_FIELD_AS_NULL are used together to address this:
FIELD_OPTIONALLY_ENCLOSED_BY: This parameter specifies the character used to enclose fields, which can differentiate between empty strings (as enclosed fields) and NULLs.
EMPTY_FIELD_AS_NULL: By setting this parameter, Snowflake interprets empty fields as NULL values when unloading data, ensuring accurate representation of NULLs versus empty strings.
These parameters are crucial when exporting data for systems that need explicit differentiation between NULL and empty string values.
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