text:   --
    -- Prepare dbSNP for the JOIN.
    --
    -- http://varianttools.sourceforge.net/Annotation/DbSNP
    -- Multiple alternate alleles sometimes correspond to the same rsid.
    -- Some variants have multiple rsids.
    --
    dbSNP AS (
    SELECT
      reference_name,
      start,
      `end`,
      reference_bases, -- on the + strand
      alternate_bases, -- on the + strand
      names AS rs_names,
      RS,
      -- Used to check for correctness of the JOIN.
      CONCAT('rs', CAST(RS AS STRING)) AS dbSNP_rsid
    FROM
      `{{ DBSNP_TABLE }}` v,
      v.alternate_bases alternate_bases )
  