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SET VARIABLE and RESET VARIABLE Statements

DuckDB supports the definition of SQL-level variables using the SET VARIABLE and RESET VARIABLE statements.

SET VARIABLE

The SET VARIABLE statement assigns a value to a variable, which can be accessed using the getvariable call:

SET VARIABLE my_var = 30;
SELECT 20 + getvariable('my_var') AS total;
total
50

If SET VARIABLE is invoked on an existing variable, it will overwrite its value:

SET VARIABLE my_var = 30;
SET VARIABLE my_var = 100;
SELECT 20 + getvariable('my_var') AS total;
total
120

Variables can have different types:

SET VARIABLE my_date = DATE '2018-07-13';
SET VARIABLE my_string = 'Hello world';
SET VARIABLE my_map = MAP {'k1': 10, 'k2': 20};

Variables can also be assigned to results of queries:

-- write some CSV files
COPY (SELECT 42 AS a) TO 'test1.csv';
COPY (SELECT 84 AS a) TO 'test2.csv';

-- add a list of CSV files to a table
CREATE TABLE csv_files(file VARCHAR);
INSERT INTO csv_files VALUES ('test1.csv'), ('test2.csv');

-- initialize a variable with the list of csv files
SET VARIABLE list_of_files = (SELECT LIST(file) FROM csv_files);

-- read the CSV files
SELECT * FROM read_csv(getvariable('list_of_files'), filename := True);
a filename
42 test.csv
84 test2.csv

If a variable is not set, the getvariable function returns NULL:

SELECT getvariable('undefined_var') AS result;
result
NULL

The getvariable function can also be used in a COLUMNS expression:

SET VARIABLE column_to_exclude = 'col1';
CREATE TABLE tbl AS SELECT 12 AS col0, 34 AS col1, 56 AS col2;
SELECT COLUMNS(c -> c != getvariable('column_to_exclude')) FROM tbl;
col0 col2
12 56

Syntax

RESET VARIABLE

The RESET VARIABLE statement unsets a variable.

SET VARIABLE my_var = 30;
RESET VARIABLE my_var;
SELECT getvariable('my_var') AS my_var;
my_var
NULL

Syntax

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