dq_customer_extract is a raw customer extract from a partner system (customer_id, full_name, email, phone, country, signup_date). Before loading it, profile how complete each column is.
For every column except `customer_id`, count the rows where the value is missing: NULL, or — for the text columns full_name, email, phone and country — a string that is empty or contains only spaces. signup_date is a date, so for it only NULL counts.
Return one row per column, including a column where nothing is missing.
Columns: column_name (the column's name as text, e.g. 'email'), missing, missing_pct (missing as a percentage of all rows, 0–100, rounded to 1 decimal place). Sort by column_name.