{
    "action": "tool_call",
    "reasoning": "I need to compute null counts and percentages for all 39 columns in raw.ae. Rather than a long UNION ALL chain, I'll use a more efficient approach with UNPIVOT or multiple aggregates in one query. Let me write a single SELECT with COUNT(*) and COUNT(column) for each column to get null counts, then filter to only columns with nulls.",
    "tool": "query_sql",
    "args": {
        "sql": "WITH null_stats AS (SELECT COUNT(*) as total_rows, COUNT(*) - COUNT(STUDYID) as STUDYID_nulls, COUNT(*) - COUNT(DOMAIN) as DOMAIN_nulls, COUNT(*) - COUNT(USUBJID) as USUBJID_nulls, COUNT(*) - COUNT(AESEQ) as AESEQ_nulls, COUNT(*) - COUNT(AESPID) as AESPID_nulls, COUNT(*) - COUNT(AETERM) as AETERM_nulls, COUNT(*) - COUNT(AELLT) as AELLT_nulls, COUNT(*) - COUNT(AELLTCD) as AELLTCD_nulls, COUNT(*) - COUNT(AEDECOD) as AEDECOD_nulls, COUNT(*) - COUNT(AEPTCD) as AEPTCD_nulls, COUNT(*) - COUNT(AEHLT) as AEHLT_nulls, COUNT(*) - COUNT(AEHLTCD) as AEHLTCD_nulls, COUNT(*) - COUNT(AEHLGT) as AEHLGT_nulls, COUNT(*) - COUNT(AEHLGTCD) as AEHLGTCD_nulls, COUNT(*) - COUNT(AEBODSYS) as AEBODSYS_nulls, COUNT(*) - COUNT(AEBDSYCD) as AEBDSYCD_nulls, COUNT(*) - COUNT(AESOC) as AESOC_nulls, COUNT(*) - COUNT(AESOCCD) as AESOCCD_nulls, COUNT(*) - COUNT(AESEV) as AESEV_nulls, COUNT(*) - COUNT(AESER) as AESER_nulls, COUNT(*) - COUNT(AEACN) as AEACN_nulls, COUNT(*) - COUNT(AEREL) as AEREL_nulls, COUNT(*) - COUNT(AEOUT) as AEOUT_nulls, COUNT(*) - COUNT(AESCAN) as AESCAN_nulls, COUNT(*) - COUNT(AESCONG) as AESCONG_nulls, COUNT(*) - COUNT(AESDISAB) as AESDISAB_nulls, COUNT(*) - COUNT(AESDTH) as AESDTH_nulls, COUNT(*) - COUNT(AESHOSP) as AESHOSP_nulls, COUNT(*) - COUNT(AESLIFE) as AESLIFE_nulls, COUNT(*) - COUNT(AESOD) as AESOD_nulls, COUNT(*) - COUNT(AEDTC) as AEDTC_nulls, COUNT(*) - COUNT(AESTDTC) as AESTDTC_nulls, COUNT(*) - COUNT(AEENDTC) as AEENDTC_nulls, COUNT(*) - COUNT(AESTDY) as AESTDY_nulls, COUNT(*) - COUNT(AEENDY) as AEENDY_nulls, COUNT(*) - COUNT(_ingestion_timestamp) as ingestion_timestamp_nulls, COUNT(*) - COUNT(_batch_id) as batch_id_nulls, COUNT(*) - COUNT(_source_file) as source_file_nulls, COUNT(*) - COUNT(_source_system) as source_system_nulls FROM raw.ae) SELECT 'AESPID' as column_name, AESPID_nulls as null_count, ROUND(100.0 * AESPID_nulls / total_rows, 2) as pct_missing FROM null_stats WHERE AESPID_nulls > 0 UNION ALL SELECT 'AEENDTC', AEENDTC_nulls, ROUND(100.0 * AEENDTC_nulls / total_rows, 2) FROM null_stats WHERE AEENDTC_nulls > 0 UNION ALL SELECT 'AESTDY', AESTDY_nulls, ROUND(100.0 * AESTDY_nulls / total_rows, 2) FROM null_stats WHERE AESTDY_nulls > 0 UNION ALL SELECT 'AEENDY', AEENDY_nulls, ROUND(100.0 * AEENDY_nulls / total_rows, 2) FROM null_stats WHERE AEENDY_nulls > 0 ORDER BY null_count DESC",
        "purpose": "Find all columns with missing values and calculate their null counts and percentages",
        "source": "raw"
    }
}