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Star Expression

Examples

-- select all columns present in the FROM clause
SELECT * FROM table_name;
-- select all columns from the table called "table_name"
SELECT table_name.* FROM table_name JOIN other_table_name USING (id);
-- select all columns except the city column from the addresses table
SELECT * EXCLUDE (city) FROM addresses;
-- select all columns from the addresses table, but replace city with lower(city)
SELECT * REPLACE (lower(city) AS city) FROM addresses;
-- select all columns matching the given expression
SELECT COLUMNS(c -> c LIKE '%num%') FROM addresses;
-- select all columns matching the given regex from the table
SELECT COLUMNS('number\d+') FROM addresses;

Syntax

Star Expression

The * expression can be used in a SELECT statement to select all columns that are projected in the FROM clause.

SELECT *
FROM tbl;

The * expression can be modified using the EXCLUDE and REPLACE.

EXCLUDE Clause

EXCLUDE allows us to exclude specific columns from the * expression.

SELECT * EXCLUDE (col)
FROM tbl;

REPLACE Clause

REPLACE allows us to replace specific columns with different expressions.

SELECT * REPLACE (col / 1000 AS col)
FROM tbl;

COLUMNS Expression

The COLUMNS expression can be used to execute the same expression on multiple columns. Like the * expression, it can only be used in the SELECT clause.

CREATE TABLE numbers (id INT, number INT);
INSERT INTO numbers VALUES (1, 10), (2, 20), (3, NULL);
SELECT min(COLUMNS(*)), count(COLUMNS(*)) FROM numbers;
min(numbers.id) min(numbers.number) count(numbers.id) count(numbers.number)
1 10 3 2

The * expression in the COLUMNS statement can also contain EXCLUDE or REPLACE, similar to regular star expressions.

SELECT min(COLUMNS(* REPLACE (number + id AS number))), count(COLUMNS(* EXCLUDE (number))) FROM numbers;
min(numbers.id) min(number := (number + id)) count(numbers.id)
1 11 3

COLUMNS expressions can also be combined, as long as the COLUMNS contains the same (star) expression:

SELECT COLUMNS(*) + COLUMNS(*) FROM numbers;
(numbers.id + numbers.id) (numbers.number + numbers.number)
2 20
4 40
6 NULL

COLUMNS Regular Expression

COLUMNS supports passing a regex in as a string constant:

SELECT COLUMNS('(id|numbers?)') FROM numbers;
id number
1 10
2 20
3 NULL

COLUMNS Lambda Function

COLUMNS also supports passing in a lambda function. The lambda function will be evaluated for all columns present in the FROM clause, and only columns that match the lambda function will be returned. This allows the execution of arbitrary expressions in order to select columns.

SELECT COLUMNS(c -> c LIKE '%num%') FROM numbers;
number
10
20
NULL

STRUCT.*

The * expression can also be used to retrieve all keys from a struct as separate columns. This is particularly useful when a prior operation creates a struct of unknown shape, or if a query must handle any potential struct keys. See the STRUCT data type and nested functions pages for more details on working with structs.

-- All keys within a struct can be returned as separate columns using *
SELECT st.* FROM (SELECT {'x': 1, 'y': 2, 'z': 3} AS st);
x y z
1 2 3
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Last modified: 2024-03-02