{
    "action": "tool_call",
    "reasoning": "The previous query returned 0 rows, which means it was looking for missing values in a way that found none. However, from the inspect_columns result (step-0), I can see that many columns show 'nulls=0', but I also see columns with range starting with '..MISSING..' which suggests a different representation of missing data. I need to check the actual data to understand how missing values are represented - they might be stored as the string 'MISSING' or empty strings rather than SQL NULLs. Let me query a sample of rows to see the actual data format.",
    "tool": "query_sql",
    "purpose": "Sample actual data from adsl to understand how missing values are represented",
    "args": {
        "sql": "SELECT RFSTDTC, RFENDTC, DTHDTC, DTHFL, DMDY FROM raw.adsl LIMIT 10",
        "purpose": "Check how missing values are actually stored in the data"
    }
}