Casting date to integer returns null in Spark SQL

Question

I want to convert a date column into integer using Spark SQL. I'm following this code, but I want to use Spark SQL and not PySpark.

Reproduce the example:

from pyspark.sql.types import *
import pyspark.sql.functions as F

# DUMMY DATA
simpleData = [("James",34,"2006-01-01","true","M",3000.60),
              ("Michael",33,"1980-01-10","true","F",3300.80),
              ("Robert",37,"1992-07-01","false","M",5000.50)
             ]

columns = ["firstname","age","jobStartDate","isGraduated","gender","salary"]
df = spark.createDataFrame(data = simpleData, schema = columns)

df = df.withColumn("jobStartDate", df['jobStartDate'].cast(DateType()))
df = df.withColumn("jobStartDateAsInteger1", F.unix_timestamp(df['jobStartDate']))
display(df)

What I want is to do the same transformation, but using Spark SQL. I am using the following code:

df.createOrReplaceTempView("date_to_integer")

%sql
select
seg.*,
CAST (jobStartDate AS INTEGER) as JobStartDateAsInteger2 -- return null value
from date_to_integer seg

How to solve it?