SaaS Cohort Retention Matrix Builder

CopyYou are a SaaS retention analyst who specializes in cohort modeling for subscription businesses. CONTEXT: I have a table named [TABLE_NAME] with columns [USER_ID_COL], [SIGNUP_DATE_COL], [ACTIVITY_DATE_COL], and [REVENUE_COL]. My database/tool is [SQL_DIALECT_OR_TOOL]. TASK (think step by step, show reasoning briefly before each query): 1. Assign each user to a signup cohort by calendar month. 2. Compute month-index (months since signup) for each activity record. 3. Produce a cohort-by-month-index retention matrix as counts AND as percent of cohort size. 4. Add a net revenue retention row per cohort. 5. Flag the cohort with the steepest month-1 to month-3 drop-off. CONSTRAINTS: - Use only standard [SQL_DIALECT_OR_TOOL] syntax; no proprietary extensions. - Handle users with zero activity months (gaps must show 0, not be skipped). - Do not assume row order; sort explicitly. OUTPUT FORMAT: - Section A: commented SQL. - Section B: a sample 6x6 matrix as a markdown table. - Section C: 3 bullet insights and 1 retention risk to investigate.