PRQL 是用于转换数据的现代化语言，也是简单、强大、管道化的 SQL 替代品。

PRQL 全称是 Pipelined Relational Query Language，读作 "Prequel"（正好和 SQL/Sequel 相反）。跟 SQL 类似，PRQL 是可读和具有声明性的；但与 SQL 不同的是，它支持变量和函数等抽象概念，以及 PRQL 是线性转化的：每一行查询都在转换前一行的结果。

示例

from tracks
filter artist == "Bob Marley"                 # Each line transforms the previous result
aggregate {                                   # `aggregate` reduces each column to a value
  plays    = sum plays,
  longest  = max length,
  shortest = min length,                      # Trailing commas are allowed
}

from employees
filter start_date > @2021-01-01               # Clear date syntax
derive {                                      # `derive` adds columns / variables
  gross_salary = salary + (tax ?? 0),         # Terse coalesce
  gross_cost = gross_salary + benefits_cost,  # Variables can use other variables
}
filter gross_cost > 0
group {title, country} (                      # `group` runs a pipeline over each group
  aggregate {                                 # `aggregate` reduces each group to a value
    average gross_salary,
    sum_gross_cost = sum gross_cost,          # `=` sets a column name
  }
)
filter sum_gross_cost > 100_000               # `filter` replaces both of SQL's `WHERE` & `HAVING`
derive id = f"{title}_{country}"              # F-strings like Python
derive country_code = s"LEFT(country, 2)"     # S-strings allow using SQL as an escape hatch
sort {sum_gross_cost, -country}               # `-country` means descending order
take 1..20                                    # Range expressions (also valid here as `take 20`)