Based on the basic information of data science practitioners, please complete the following analysis step by step.

Read the data from the csv file $"$ds$\_$salaries.csv$",$ and create a dataframe object.

Calculate the total number of employees in different job positions $($i$.$e$.$ the column "job$\_$title"$).$

Calculate the mean and variance of employee income $($i$.$e$.$ the column "salary$\_$in$\_$usd"$)$ in different company sizes $($i$.$e$.$ the column "company$\_$size"$).$

Analyze the relationship $($e$.$g$.$ correlation coefficient$)$ between three columns $($i$.$e$.$ "salary$\_$in$\_$usd", "experience$\_$level" and "company$\_$size"$).$