DataHandle

-- In the SQL the table is called data; each ? takes the next value.
local sql = "SELECT SUM(loaves) AS total FROM data WHERE item = ?"
local buns = sales:query(sql, { "Buns" })
for _, row in buns:rows() do
    print(row.total) --> 54
end

-- A table per row, keyed by column; columns picks which to read.
for i, row in sales:rows({ columns = { "item", "loaves" } }) do
    print(i, row.item, row.loaves, row.day) --> 1 Bread 12 nil
    break
end

-- Columns of up to size rows at a time; get counts from 1 in each.
local total = 0
for _, batch in sales:batches({ size = 3 }) do
    local loaves = batch:column("loaves")
    for i = 1, batch:len() do
        total = total + loaves:get(i)
    end
end
print(total) --> 75

local schema = sales:schema()
print(schema:len(), schema:field("loaves"):dtype()) --> 3 int64

-- A mark bound to the view draws its rows downsampled to the
-- pixel budget.
local lines = { "t,v" }
for t = 1, 1000 do
    lines[#lines + 1] = t .. "," .. math.sin(t / 50)
end
local wave = datumhue.bytes(table.concat(lines, "\n")):csv()
local view =
    wave:view({ x_column = "t", y_column = "v", pixel_width = 100 })
print(view:range().x_max) --> 1000.0

local tuesday =
    sales:query("SELECT item, loaves FROM data WHERE day = 'Tue'")
local encoded = tuesday:encode_csv()
print(encoded:text()) --> item,loaves Bread,9 Buns,24

-- A query runs when first read; ready runs it now, and raises if it
-- fails.
local typo = sales:query("SELECT loaf FROM data")
print(typo.state) --> pending
local ok = pcall(function()
    typo:ready()
end)
print(ok, typo.state) --> false failed