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SELECT

Dremio supports querying using standard SELECT statements. You can query tables and views that are contained in Dremio’s space entity (including your home space) and in the sources that are connected to Dremio (such as Amazon S3 and Oracle).

When working with Apache Iceberg tables, you can query a table’s metadata as well as run queries by snapshot ID.

note:

For Apache Iceberg tables, Dremio supports only the copy-on-write storage mechanism and reads only the latest data files for each Iceberg v2 table that you run SQL commands against. Dremio does not support Iceberg v2 tables that have merge-on-read manifests.

Querying a Table’s Data

Syntax

[ WITH ... ] 
SELECT [ ALL | DISTINCT ] 

  {
    { * | <column_name1>, <column_name2>, ... } FROM { <table_name> | <view_name> | TABLE( <iceberg_metadata> ( '<table_name>' ) ) }
    [ { PIVOT | UNPIVOT } ( <expression> ) ]
    [ JOIN <expression> ]
    [ WHERE <condition> ]
    [ GROUP BY <expression> ]
    [ QUALIFY <expression> ]
    [ ORDER BY <column_name1>, <column_name2>, ... [ DESC ] ]
    [ LIMIT <count> ]

    [ AT {
      SNAPSHOT '<snapshot_id>'
      | <timestamp>
      }
    ]
  }

Parameters

Defines a common table expression (CTE), which is a named subquery. For more information, read WITH.

Specifies the result set that is returned. Similar to the asterisk (*), ALL returns all the values in the result set. DISTINCT eliminates duplicates from the result set. If you do not specify an option, the default is ALL.

Indicates that you want to query all columns in the table.

The name of the column(s) that you want to query.

The path to the source that you want to query a table in. The source can be in a space, your scratch directory, an Arctic catalog, or a data source.

For <iceberg_metadata>, Iceberg includes helpful system-table references which provide easy access to Iceberg-specific information on tables, including:

The data files for a table
The history of a table
The manifest files for a table
The snapshots for a table

Supported Iceberg metadata clauses include:

TABLE( table_files( '<table_name>' ) ): Query an Iceberg table's data file metadata using the table_files() function. Dremio returns records that have these fields:

Column	Data Type	Description
file_path	VARCHAR	Full file path and name
file_format	VARCHAR	Format, for example, PARQUET
record_count	BIGINT	Number of rows
file_size_in_bytes	BIGINT	Size of the file
column_sizes	VARCHAR	List of columns with the size of each column
value_counts	VARCHAR	List of columns with the number of records with a value
null_value_counts	VARCHAR	List of columns with the number of records as NULL
nan_value_counts	VARCHAR	List of columns with the number of records as NaN
lower_bounds	VARCHAR	List of columns with the lower bound of each
upper_bounds	VARCHAR	List of columns with the upper bound of each
key_metadata	VARCHAR	Key metrics
split_offsets	VARCHAR	Split offsets

TABLE( table_history( '<table_name>' ) ): Query an Iceberg table's history metadata using the table_history() function. Dremio returns records that have these fields:

Column	Data Type	Description
made_current_at	TIMESTAMP	The timestamp the Iceberg snapshot was made at
snapshot_id	VARCHAR	The Iceberg snapshot
parent_id	VARCHAR	The parent snapshot ID, null if not exists
is_current_ancestor	BOOLEAN	If the snapshot is part of the current history, shows abandoned snapshots

TABLE( table_manifests( '<table_name>' ) ): Query an Iceberg table's manifest file metadata using the table_manifests() function. Dremio returns records that have these fields:

Column	Data Type	Description
path	VARCHAR	Full path and name of the manifest file
length	BIGINT	Size in bytes
partition_spec_id	VARCHAR	ID of the partition
added_snapshot_id	VARCHAR	ID of the snapshot added to the manifest
added_data_files_count	BIGINT	Number of new data files added
existing_data_files_count	BIGINT	Number of existing data files
deleted_data_files_count	BIGINT	Number of files removed
partition_summaries	VARCHAR	Partition information

TABLE( table_snapshot( '<table_name>' ) ): Query an Iceberg table's snapshot metadata using the table_snapshot() function. Dremio returns records that have these fields:

Column	Data Type	Description
committed_at	TIMESTAMP	The timestamp the Iceberg snapshot was committed
snapshot_id	VARCHAR	The Iceberg snapshot ID
parent_id	VARCHAR	The parent snapshot ID, null if it does not exist
operation	VARCHAR	The Iceberg operation (for example, append)
manifest_list	VARCHAR	List of manifest files for the snapshot
summary	VARCHAR	Additional attributes (records added, etc.)

PIVOT converts a set of data from rows into columns. UNPIVOT converts a set of data from columns into rows. The expression can be one of the following:

pivot_clause: The query to aggregate the data on.
pivot_for_clause: Which columns to group and pivot on.
pivot_in_clause: Filters the values for the columns pivot_for_clause. Each of the values in this clause will be a separate column.

Note:

This keyword is applied to a SELECT statement. The syntax does not support an alias between the table/subquery and either the PIVOT or UNPIVOT clause. For example, SELECT name, dept FROM employees) <alias> PIVOT <query> is not supported.

Combines rows from two tables or views to create a new combined row that can be used in the query. Supported expressions are LEFT [OUTER] JOIN, RIGHT [OUTER] JOIN, FULL [OUTER] JOIN, INNER JOIN, CROSS JOIN.

Use the WHERE clause to filter your query and extract only the records that fulfill a specified condition. The following operators can be used: +, >, <, >=, <=, { <> | != }, BETWEEN, LIKE, IN. Additionally, <condition> can include logical operators, such as AND, OR, and NOT.

Groups rows with the same group-by-item expressions and computes aggregate functions (such as COUNT(), MAX(), MIN(), SUM(), AVG() ) for the resulting group. A GROUP BY expression can be one or more column names, a number referencing a position in the SELECT list, or a general expression.

Filters the results of window functions. To use QUALIFY, at least one window function must be present in either the SELECT statement or within the QUALIFY expression. The expression filters the result after aggregates and window functions are computed; it can also contain window functions. The boolean expression can be the result of a subquery.

Sort the result by a specific column. By default, the records are sorted in ascending order. Use DESC to sort the records in descending order.

Constrains the maximum number of rows returned by the query. Must be a non-negative integer.

Specifies a reference for the current SQL session. When this parameter is omitted, the current reference is used.

SNAPSHOT '<snapshot_id>': Applies to Apache Iceberg tables only. A time-travel query that enables you to specify an earlier version of a table to read. A snapshot ID is obtained either through the table_history() or table_snapshot() metadata function.
<timestamp>: Available for Iceberg table queries only. Changes the commit reference point to the most recent Iceberg snapshot as of the provided timestamp. <timestamp> may be any SQL expression that resolves to a single timestamp type value, for example: CAST( DATE_SUB(CURRENT_DATE,1) AS TIMESTAMP ) or TIMESTAMP '2022-07-01 01:30:00.000'.

Examples

Query an existing table in a data lake source

SELECT * 
FROM Samples."samples.dremio.com"."zips.json"

Query a specified column in an existing table

SELECT city 
FROM Samples."samples.dremio.com"."zips.json"

Query a table using the DISTINCT option to eliminate duplicates from the result set

SELECT DISTINCT city 
FROM Samples."samples.dremio.com"."zips.json"

Query a table and filter the results using the WHERE clause

SELECT * 
FROM Samples."samples.dremio.com"."zips.json"
WHERE state = 'MA' AND city = 'AGAWAM'

Query a table and group and order the result by the specified expression

SELECT COUNT(city), city, state
FROM Samples."samples.dremio.com"."zips.json"
GROUP BY state, CITY
ORDER BY COUNT(city) DESC

Query a table and filter the result using QUALIFY with window functions in the SELECT list

SELECT passenger_count, trip_distance_mi, fare_amount,
RANK() OVER (PARTITION BY passenger_count ORDER BY trip_distance_mi) AS pc_rank
FROM "NYC-taxi-trips"
QUALIFY pc_rank = 1

Query a table and filter the result using QUALIFY with window functions in the QUALIFY clause

SELECT passenger_count, trip_distance_mi, fare_amount
FROM "NYC-taxi-trips"
QUALIFY RANK() OVER (PARTITION BY passenger_count ORDER BY trip_distance_mi) = 1

Query a table using the PIVOT and UNPIVOT clauses

ALTER DATASET Samples."samples.dremio.com"."SF weather 2018-2019.csv" REFRESH METADATA auto promotion FORCE UPDATE;

SELECT * FROM (
    SELECT  EXTRACT(YEAR FROM CAST(F AS DATE)) as "YEAR",
            EXTRACT(MONTH FROM CAST(F AS DATE)) as "MONTH",
            K as MAX_TEMP
    FROM Samples."samples.dremio.com"."SF weather 2018-2019.csv"
    where F <> 'DATE'
)
PIVOT (
    max(MAX_TEMP) for "MONTH" in (1 as JAN, 2 as FEB, 3 as MAR, 4 as APR, 5 as MAY, 6 as JUN, 7 as JUL, 8 as AUG, 9 as SEP, 10 as OCT, 11 as NOV, 12 as "DEC")
)
UNPIVOT (
    GLOBAL_MAX_TEMP for "MONTH" in (JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, "DEC")
)
ORDER BY "YEAR", "MONTH";

Left join

SELECT
  c.c_nationkey,
  o.o_orderdate,
  o.o_shippriority
FROM
  (NAS2."customer.parquet" c
  left join
  NAS2."orders.parquet" as o
ON c.c_custkey = o.o_custkey)

Right join

SELECT
  c.c_nationkey,
  o.o_orderdate,
  o.o_shippriority
FROM
  (NAS2."customer.parquet" c
  right join
  NAS2."orders.parquet" as o
ON c.c_custkey = o.o_custkey)

Full join

SELECT
  c.c_nationkey,
  o.o_orderdate,
  o.o_shippriority
FROM
  (NAS2."customer.parquet" c
  full join
  NAS2."orders.parquet" as o
ON c.c_custkey = o.o_custkey)

Inner join

SELECT
  c.c_nationkey,
  o.o_orderdate,
  o.o_shippriority
FROM
  (NAS2."customer.parquet" c
  inner join
  NAS2."orders.parquet" as o
ON c.c_custkey = o.o_custkey)

Cross join

SELECT
  c.c_nationkey,
  o.o_orderdate,
  o.o_shippriority
FROM
  (NAS2."customer.parquet" c
  cross join
  NAS2."orders.parquet" as o)

Examples for Iceberg Tables

Time travel query on an Iceberg table using a timestamp

SELECT count(*) 
FROM my_table AT TIMESTAMP '2022-07-01 01:30:00.000'

Time travel query on an Iceberg table using a snapshot ID

SELECT * 
FROM myTable AT SNAPSHOT '5393090506354317772'

Query an Iceberg table using the table's history metadata and a snapshot ID

SELECT * 
FROM TABLE(table_history('myTable')) 
WHERE snapshot_id = 4593468819579153853

Query an Iceberg table to find the number of snapshots for a table

SELECT count(*) 
FROM TABLE(table_snapshot('myTable')) 
GROUP BY snapshot_id

Distributing Data Evenly Across Executor Nodes During Joins

You can use a BROADCAST hint if a query profile indicates that data involved in a join of two tables is heavily skewed and overloading one or more executor nodes. The hint forces an even distribution of the data across all executor nodes.

note:

These hints are ignored for nested-loop joins.

A BROADCAST hint must be used immediately after the name of a table.

Syntax of a BROADCAST hint

/*+ BROADCAST */

Example 1

SELECT * 
  FROM T1 /*+ BROADCAST */ 
  INNER JOIN t2 ON t1.key = t2.key 
  INNER JOIN t3 ON t2.key = t3.key

Example 2

SELECT * 
  FROM T1 
  INNER JOIN (select key, max(cost) cost from t2 /*+ BROADCAST */) T2 ON t1.key = t2.key 
  INNER JOIN t3 ON t2.key = t3.key

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