{
    "action": "tool_call",
    "reasoning": "I've already identified several data quality issues from the evidence: (1) AESTDTC has 7 pre-2000 values (min 1977), (2) 473 rows have end dates before start dates, (3) 26 rows have bad AESTDTC format, (4) 473 rows have bad AEENDTC format, (5) all AEENDTC values are missing. Now I need to examine the specific problematic values to characterize these issues more precisely. Let me look at the pre-2000 start dates and the format issues.",
    "tool": "query_sql",
    "args": {
        "sql": "SELECT USUBJID, AESEQ, AESTDTC, AEENDTC, AEDTC, AESTDY, AEENDY FROM raw.ae WHERE CAST(AESTDTC AS VARCHAR) < '2000' OR LENGTH(AESTDTC) != 10 OR AESTDTC NOT LIKE '____-__-__' ORDER BY AESTDTC LIMIT 50",
        "purpose": "Examine the pre-2000 dates and format issues in AESTDTC to characterize the data quality problems",
        "source": "raw"
    }
}