如何使用 python 在 spark SQL 中传递变量？

Question

I am writing spark code in python. How do I pass a variable in a spark.sql query?

    q25 = 500
    Q1 = spark.sql("SELECT col1 from table where col2>500 limit $q25 , 1")

Currently the above code does not work? How do we pass variables?

I have also tried,

    Q1 = spark.sql("SELECT col1 from table where col2>500 limit q25='{}' , 1".format(q25))

Answer 1

You need to remove single quote and q25 in string formatting like this:

Q1 = spark.sql("SELECT col1 from table where col2>500 limit {}, 1".format(q25))

Update:

Based on your new queries:

spark.sql("SELECT col1 from table where col2>500 order by col1 desc limit {}, 1".format(q25))

Note that the SparkSQL does not support OFFSET, so the query cannot work.

If you need add multiple variables you can try this way:

q25 = 500
var2 = 50
Q1 = spark.sql("SELECT col1 from table where col2>{0} limit {1}".format(var2,q25))

Answer 2

All you need to do is add s (String interpolator) to the string. This allows the usage of variable directly into the string.

val q25 = 10
Q1 = spark.sql(s"SELECT col1 from table where col2>500 limit $q25)

Answer 3

Another option if you're doing this sort of thing often or want to make your code easier to re-use is to use a map of configuration variables and the format option:

configs = {"q25":10,
           "TABLE_NAME":"my_table",
           "SCHEMA":"my_schema"}
Q1 = spark.sql("""SELECT col1 from {SCHEMA}.{TABLE_NAME} 
                  where col2>500 
                  limit {q25}
               """.format(**configs))

Answer 4

A really easy solution is to store the query as a string (using the usual python formatting), and then pass it to the spark.sql() function:

q25 = 500

query = "SELECT col1 from table where col2>500 limit {}".format(q25)

Q1 = spark.sql(query)

Answer 5

Using f-Strings approach (PySpark):

table = 'my_schema.my_table'

df = spark.sql(f'select * from {table}')