本文共 4108 字，大约阅读时间需要 13 分钟。
原文地址： http://www.cnblogs.com/bluefrog/archive/2012/05/16/2504625.html
本来是项目合作的，可是你却一而再再而三的使用这招，我处理愤怒了，自己来。先学习下 mnesia 的操作先：
-module(test_mnesia).-compile(export_all).-include_lib("stdlib/include/qlc.hrl").%% 定义记录结构-record(shop,{item,quantity,cost}).-record(cost,{name,price}).-record(design,{id,plan}).start() -> mnesia:start(), %% 等待表的加载 mnesia:wait_for_tables([shop,cost,design],20000).%% 初始化mnesia表结构init() -> mnesia:create_schema([node()]), mnesia:start(), %% 表创建 mnesia:create_talbe(TableName,[Args]) %% {type,Type} set,ordered_set,bag 表类型 %% {ram_copies,NodeList} NodeList每个节点都有内存备份 默认为这个{ram_copies,[node()]} %% {disc_copies,NodeList} NodeList每个节点都有内存备份和磁盘备份 %% {disc_only_copies,NodeList} NodeList每个节点有磁盘备份 %% {attributes,AtomList} 要保存的列名称 一般和record有关 record_info(fields,RecordName) mnesia:create_table(shop,[{attributes,record_info(fields,shop)}]), %% 创建shop表 mnesia:create_table(cost,[{attributes,record_info(fields,cost)}]), mnesia:create_table(design,[{attributes,record_info(fields,design)}]), mnesia:stop().%% 加载测试数据reset_tables() -> mnesia:clear_table(shop), mnesia:clear_table(cost), F = fun() -> lists:foreach(fun mnesia:write/1,example_tables()) end, mnesia:transaction(F).%% 测试数据example_tables() -> [ %% shop table {shop,apple,20,2.3}, {shop,orange,100,3.8}, {shop,pear,200,3.6}, {shop,banana,420,4.5}, {shop,potato,2456,1.2}, %% cost table {cost,apple,1.5}, {cost,orange,2.4}, {cost,pear,2.2}, {cost,banana,1.6}, {cost,potato,0.6} ].%%== 查询 =============================================================do(Q) -> F = fun() -> qlc:e(Q) end, {atomic,Val} = mnesia:transaction(F), Val.%% SELECT * FROM shop%% 选取所有列demo(select_shop) -> do(qlc:q([X || X <- mnesia:table(shop)]));%% SELECT item,quantity FROM shop%% 选取指定列demo(select_some) -> do(qlc:q([{X#shop.item, X#shop.quantity} || X <- mnesia:table(shop)]));%% SELECT * FROM shop WHERE shop.quantity < 250%% 选取指定条件的数据demo(where) -> do(qlc:q([X || X <- mnesia:table(shop), X#shop.quantity < 250 ]));%% 关联查询%% SELECT shop.* FROM shop,cost wHERE shop.item = cost.name AND cost.price < 2 AND shop.quantity < 250demo(join) -> do(qlc:q([X || X <- mnesia:table(shop), X#shop.quantity < 250, Y <- mnesia:table(cost), X#shop.item =:= Y#cost.name, Y#cost.price < 2 ])).%% == 数据操作 ===============================================%% 增加一行add_shop_item(Name,Quantity,Cost) -> Row = #shop{item = Name,quantity = Quantity, cost = Cost}, F = fun() -> mnesia:write(Row) end, mnesia:transaction(F).%% 删除一行remove_shop_item(Item) -> Oid = {shop,Item}, F = fun() -> mnesia:delete(Oid) end, mnesia:transaction(F).%% 取消一个事务former(Nwant) -> F = fun() -> %% find the num of apples [Apple] = mnesia:read({shop,apple}), Napples = Apple#shop.quantity, %% update the database NewApple = Apple#shop{quantity = Napples + 2 * Nwant}, mnesia:write(NewApple), %% find the num of oranges [Orange] = mnesia:read({shop,orange}), Noranges = Orange#shop.quantity, if Noranges >= Nwant -> %% update the database Num = Noranges - Nwant, NewOrange = Orange#shop{quantity = Num}, mnesia:write(NewOrange); true -> %% no enough oranges 取消事务 mnesia:abort(oranges) end end, mnesia:transaction(F).%% 保存复杂数据add_plans() -> D1 = #design{ id = {joe,1}, plan = {circle,10} }, D2 = #design{ id = fred, plan = {rectangle,[10,5]} }, F = fun() -> mnesia:write(D1), mnesia:write(D2) end, mnesia:transaction(F).%% 获复杂数据get_plans(PlanId) -> F = fun() -> mnesia:read({design,PlanId}) end, mnesia:transaction(F).