Select

Picks and computes columns.

select [
  {name} = {expression},
  # or
  {column},
]
# or
select ![{column}]

Examples

PRQL

from employees
select name = f"{first_name} {last_name}"

SQL

SELECT
  CONCAT(first_name, ' ', last_name) AS name
FROM
  employees

PRQL

from employees
select [
  name = f"{first_name} {last_name}",
  age_eoy = dob - @2022-12-31,
]

SQL

SELECT
  CONCAT(first_name, ' ', last_name) AS name,
  dob - DATE '2022-12-31' AS age_eoy
FROM
  employees

PRQL

from employees
select first_name

SQL

SELECT
  first_name
FROM
  employees

PRQL

from e=employees
select [e.first_name, e.last_name]

SQL

SELECT
  first_name,
  last_name
FROM
  employees AS e

Excluding columns

We can use ! to exclude a list of columns. This can operate in two ways:

  • We use SELECT * EXCLUDE / SELECT * EXCEPT for the columns supplied to select ![] in dialects which support it.
  • Otherwise, the columns must have been defined prior in the query (unless all of a table’s columns are excluded); for example in another select or a group transform. In this case, we evaluate and specify the columns that should be included in the output SQL.

Some examples:

PRQL

prql target:sql.bigquery
from tracks
select ![milliseconds,bytes]

SQL

SELECT
  *
EXCEPT
  (milliseconds, bytes)
FROM
  tracks

PRQL

from tracks
select [track_id, title, composer, bytes]
select ![title, composer]

SQL

SELECT
  track_id,
  bytes
FROM
  tracks

PRQL

from artists
derive nick = name
select ![artists.*]

SQL

SELECT
  name AS nick
FROM
  artists

Note

In the final example above, the e representing the table / namespace is no longer available after the select statement. For example, this would raise an error:

from e=employees
select e.first_name
filter e.first_name == "Fred" # Can't find `e.first_name`

To refer to the e.first_name column in subsequent transforms, either refer to it using first_name, or if it requires a different name, assign one in the select statement:

PRQL

from e=employees
select fname = e.first_name
filter fname == "Fred"

SQL

WITH table_1 AS (
  SELECT
    first_name AS fname
  FROM
    employees AS e
)
SELECT
  fname
FROM
  table_1
WHERE
  fname = 'Fred'

`