Kepler: Using a Database

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There is a few libraries to access databases with Lua out there, but only [LuaSQL](http://www.keplerproject.org/luasql/)provides uniform access to different databases.

Here is a simple example of how to use LuaSQL:

-- Initialization (1)
    require"luasql.postgres"
    local env = luasql.postgres ()
    local conn = assert (env:connect ("lpg"))
    
    -- Building SQL statement (2)
    course_list = { "Music", "Literature", }
    for i, course in ipairs (course_list) do
        course_list[i] = "'"..course.."'"
    end
    local c_list = table.concat (course_list, ",")
    local stmt = [=[
        select a.id, a.name
            from alumn a inner join course c on (a.course_id = c.id)
            where c.name in (]=]..c_list..")"
    
    -- SQL execution and error handling (3)
    local cur, err = conn:execute (stmt)
    if not cur then
        error (err.." SQL = [=["..stmt.."]=]")
    end
    
    -- Iteration loop (4)
    local id, name = cur:fetch ()
    while id do
        cgilua.put (string.format ("<tr><td>id = %%s<td>name = %%s</tr>", id, name))
        id, name = cur:fetch ()
    end

However, it would be better to define an iterator in order to use it inside a LuaPage:

function lines (stmt)
        local cur = assert (conn:execute(stmt))
        return function ()
            return cur:fetch()
        end
    end

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