{"id":126,"date":"2008-05-01T17:28:23","date_gmt":"2008-05-01T17:28:23","guid":{"rendered":""},"modified":"2008-05-01T17:28:23","modified_gmt":"2008-05-01T17:28:23","slug":"126","status":"publish","type":"post","link":"https:\/\/www.poloo.org\/?p=126","title":{"rendered":"LINQ\u4f53\u9a8c(7)\u2014\u2014LINQ to SQL\u8bed\u53e5\u4e4bGroup By\/Having\u548cExists"},"content":{"rendered":"

Group By\/Having\u64cd\u4f5c\u7b26<\/font><\/h1>\n

\u9002\u7528\u573a\u666f<\/strong>\uff1a\u5206\u7ec4\u6570\u636e\uff0c\u4e3a\u6211\u4eec\u67e5\u627e\u6570\u636e\u7f29\u5c0f\u8303\u56f4\u3002<\/p>\n

\u8bf4\u660e<\/strong>\uff1a\u5206\u914d\u5e76\u8fd4\u56de\u5bf9\u4f20\u5165\u53c2\u6570\u8fdb\u884c\u5206\u7ec4\u64cd\u4f5c\u540e\u7684\u53ef\u679a\u4e3e\u5bf9\u8c61\u3002\u5206\u7ec4\uff1b\u5ef6\u8fdf<\/p>\n

1.\u7b80\u5355\u5f62\u5f0f\uff1a<\/h2>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect <\/span>g;<\/pre>\n
\u8bf4\u660e\uff1afrom p in db.Products \u8868\u793a\u4ece\u8868\u4e2d\u5c06\u4ea7\u54c1\u5bf9\u8c61\u53d6\u51fa\u6765\u3002group p by p.CategoryID into g\u8868\u793a\u5bf9p\u6309CategoryID\u5b57\u6bb5\u5f52\u7c7b\u3002\u5176\u7ed3\u679c\u547d\u540d\u4e3ag\uff0c\u4e00\u65e6\u91cd\u65b0\u547d\u540d\uff0cp\u7684\u4f5c\u7528\u57df\u5c31\u7ed3\u675f\u4e86\uff0c\u6240\u4ee5\uff0c\u6700\u540eselect\u65f6\uff0c\u53ea\u80fdselect g\u3002\u5f53\u7136\uff0c\u4e5f\u4e0d\u5fc5\u91cd\u65b0\u547d\u540d\u53ef\u4ee5\u8fd9\u6837\u5199\uff1a<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID;<\/pre>\n
\u6211\u4eec\u7528\u793a\u610f\u56fe\u8868\u793a\uff1a
\n\"\"<\/p>\n
 <\/p>\n
\u5982\u679c\u60f3\u904d\u5386\u67d0\u7c7b\u522b\u4e2d\u6240\u6709\u8bb0\u5f55\uff0c\u8fd9\u6837\uff1a<\/p>\n
foreach <\/span>(var <\/span>gp in <\/span>q)\r\n{\r\nif <\/span>(gp.Key == 2)\r\n{\r\nforeach <\/span>(var <\/span>item in <\/span>gp)\r\n{\r\n\/\/do something\r\n<\/span>}\r\n}\r\n}<\/pre>\n
2.Select\u533f\u540d\u7c7b\uff1a<\/h2>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{ CategoryID = g.Key, g }; <\/pre>\n
\u8bf4\u660e\uff1a\u5728\u8fd9\u53e5LINQ\u8bed\u53e5\u4e2d\uff0c\u67092\u4e2aproperty\uff1aCategoryID\u548cg\u3002\u8fd9\u4e2a\u533f\u540d\u7c7b\uff0c\u5176\u5b9e\u8d28\u662f\u5bf9\u8fd4\u56de\u7ed3\u679c\u96c6\u91cd\u65b0\u8fdb\u884c\u4e86\u5305\u88c5\u3002\u628ag\u7684property\u5c01\u88c5\u6210\u4e00\u4e2a\u5b8c\u6574\u7684\u5206\u7ec4\u3002\u5982\u4e0b\u56fe\u6240\u793a\uff1a\"\"<\/p>\n
 <\/p>\n
\u5982\u679c\u60f3\u904d\u5386\u67d0\u533f\u540d\u7c7b\u4e2d\u6240\u6709\u8bb0\u5f55\uff0c\u8981\u8fd9\u4e48\u505a\uff1a<\/p>\n
foreach <\/span>(var <\/span>gp in <\/span>q)\r\n{\r\nif <\/span>(gp.CategoryID == 2)\r\n{\r\nforeach <\/span>(var <\/span>item in <\/span>gp.g)\r\n{\r\n\/\/do something\r\n<\/span>}\r\n}\r\n}<\/pre>\n
3.\u6700\u5927\u503c<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u5224\u65ad\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u4e2d\u5355\u4ef7\u6700\u5927\u7684Products\u3002\u53d6\u51faCategoryID\u503c\uff0c\u5e76\u628aUnitPrice\u503c\u8d4b\u7ed9MaxPrice\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nMaxPrice = g.Max(p => p.UnitPrice)\r\n};<\/pre>\n
4.\u6700\u5c0f\u503c<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u5224\u65ad\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u4e2d\u5355\u4ef7\u6700\u5c0f\u7684Products\u3002\u53d6\u51faCategoryID\u503c\uff0c\u5e76\u628aUnitPrice\u503c\u8d4b\u7ed9MinPrice\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nMinPrice = g.Min(p => p.UnitPrice)\r\n};<\/pre>\n
5.\u5e73\u5747\u503c<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u53d6\u51faCategoryID\u503c\u548c\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u4e2d\u5355\u4ef7\u7684\u5e73\u5747\u503c\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nAveragePrice = g.Average(p => p.UnitPrice)\r\n};<\/pre>\n
6.\u6c42\u548c<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u53d6\u51faCategoryID\u503c\u548c\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u4e2d\u5355\u4ef7\u7684\u603b\u548c\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nTotalPrice = g.Sum(p => p.UnitPrice)\r\n};<\/pre>\n
7.\u8ba1\u6570<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u53d6\u51faCategoryID\u503c\u548c\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u7684\u6570\u91cf\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nNumProducts = g.Count()\r\n};<\/pre>\n
8.\u5e26\u6761\u4ef6\u8ba1\u6570<\/h2>\n
\u8bf4\u660e\uff1a\u5148\u6309CategoryID\u5f52\u7c7b\uff0c\u53d6\u51faCategoryID\u503c\u548c\u5404\u4e2a\u5206\u7c7b\u4ea7\u54c1\u7684\u65ad\u8d27\u6570\u91cf\u3002 Count\u51fd\u6570\u91cc\uff0c\u4f7f\u7528\u4e86Lambda\u8868\u8fbe\u5f0f\uff0cLambda\u8868\u8fbe\u5f0f\u4e2d\u7684p\uff0c\u4ee3\u8868\u8fd9\u4e2a\u7ec4\u91cc\u7684\u4e00\u4e2a\u5143\u7d20\u6216\u5bf9\u8c61\uff0c\u5373\u67d0\u4e00\u4e2a\u4ea7\u54c1\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nselect new <\/span>{\r\ng.Key,\r\nNumProducts = g.Count(p => p.Discontinued)\r\n};<\/pre>\n
9.Where\u9650\u5236<\/h2>\n
\u8bf4\u660e\uff1a\u5728\u7ffb\u8bd1\u6210SQL\u8bed\u53e5\u65f6\uff0c\u5728\u6700\u5916\u5c42\u5d4c\u5957\u4e86Where\u6761\u4ef6\u3002<\/p>\n
var <\/span>q =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by <\/span>p.CategoryID into <\/span>g\r\nwhere <\/span>g.Count() >= 10\r\nselect new <\/span>{\r\ng.Key,\r\nProductCount = g.Count()\r\n};<\/pre>\n
\u8bed\u53e5\u63cf\u8ff0\uff1a\u6839\u636e\u4ea7\u54c1\u7684\u2015ID\u5206\u7ec4\uff0c\u67e5\u8be2\u4ea7\u54c1\u6570\u91cf\u5927\u4e8e10\u7684ID\u548c\u4ea7\u54c1\u6570\u91cf\u3002<\/p>\n
10.Multiple Columns<\/h2>\n
\u8bf4\u660e\uff1a\u65e2\u6309\u4ea7\u54c1\u7684\u5206\u7c7b\uff0c\u53c8\u6309\u4f9b\u5e94\u5546\u5206\u7c7b\u3002\u5728by\u540e\u9762\uff0cnew\u51fa\u6765\u4e00\u4e2a\u533f\u540d\u7c7b\u3002\u8fd9\u91cc\uff0cKey\u5176\u5b9e\u8d28\u662f\u4e00\u4e2a\u7c7b\u7684\u5bf9\u8c61\uff0cKey\u5305\u542b\u4e24\u4e2aProperty\uff1aCategoryID\u3001SupplierID\u3002\u7528g.Key.CategoryID\u53ef\u4ee5\u904d\u5386CategoryID\u7684\u503c\u3002<\/p>\n
var <\/span>categories =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by new\r\n<\/span>{\r\np.CategoryID,\r\np.SupplierID\r\n}\r\ninto <\/span>g\r\nselect new\r\n<\/span>{\r\ng.Key,\r\ng\r\n};<\/pre>\n
11.Expression(\u8868\u8fbe\u5f0f)<\/h2>\n
\u8bf4\u660e\uff1a\u6309\u4ea7\u54c1\u5355\u4ef7\u662f\u5426\u5927\u4e8e10\u5206\u7c7b\u3002\u5176\u7ed3\u679c\u5206\u4e3a\u4e24\u7c7b\uff0c\u5927\u4e8e\u7684\u662f\u4e00\u7c7b\uff0c\u5c0f\u4e8e\u53ca\u7b49\u4e8e\u4e3a\u53e6\u4e00\u7c7b\u3002<\/p>\n
var <\/span>categories =\r\nfrom <\/span>p in <\/span>db.Products\r\ngroup <\/span>p by new <\/span>{ Criterion = p.UnitPrice > 10 } into <\/span>g\r\nselect <\/span>g;<\/pre>\n
Exists\/In\/Any\/All\/Contains\u64cd\u4f5c\u7b26<\/h1>\n
\u9002\u7528\u573a\u666f<\/strong>\uff1a\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u5143\u7d20\uff0c\u8fdb\u4e00\u6b65\u7f29\u5c0f\u8303\u56f4\u3002<\/p>\n
Any<\/h1>\n
\u8bf4\u660e\uff1a\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u662f\u5426\u6709\u5143\u7d20\u6ee1\u8db3\u67d0\u4e00\u6761\u4ef6\uff1b\u4e0d\u5ef6\u8fdf\u3002\uff08\u82e5\u6761\u4ef6\u4e3a\u7a7a\uff0c\u5219\u96c6\u5408\u53ea\u8981\u4e0d\u4e3a\u7a7a\u5c31\u8fd4\u56deTrue\uff0c\u5426\u5219\u4e3aFalse\uff09\u3002\u67092\u79cd\u5f62\u5f0f\uff0c\u5206\u522b\u4e3a\u7b80\u5355\u5f62\u5f0f\u548c\u5e26\u6761\u4ef6\u5f62\u5f0f\u3002<\/p>\n
1.\u7b80\u5355\u5f62\u5f0f\uff1a<\/h2>\n
var <\/span>q =\r\nfrom <\/span>c in <\/span>db.Customers\r\nwhere <\/span>!c.Orders.Any()\r\nselect <\/span>c;<\/pre>\n
\u751f\u6210SQL\u8bed\u53e5\u4e3a\uff1a<\/p>\n
Select <\/span>[t0].[CustomerID], [t0].[CompanyName], [t0].[ContactName],\r\n[t0].[ContactTitle], [t0].[Address], [t0].[City], [t0].[Region],\r\n[t0].[PostalCode], [t0].[Country], [t0].[Phone], [t0].[Fax]\r\nFROM <\/span>[dbo].[Customers] AS <\/span>[t0]\r\nWhere NOT <\/span>(EXISTS<\/span>(\r\nSelect NULL AS <\/span>[EMPTY] FROM <\/span>[dbo].[Orders] AS <\/span>[t1]\r\nWhere <\/span>[t1].[CustomerID] = [t0].[CustomerID]\r\n))<\/pre>\n
2.\u5e26\u6761\u4ef6\u5f62\u5f0f\uff1a<\/h2>\n
var <\/span>q =\r\nfrom <\/span>c in <\/span>db.Categories\r\nwhere <\/span>c.Products.Any(p => p.Discontinued)\r\nselect <\/span>c;<\/pre>\n
\u751f\u6210SQL\u8bed\u53e5\u4e3a\uff1a<\/p>\n
Select <\/span>[t0].[CategoryID], [t0].[CategoryName], [t0].[Description],\r\n[t0].[Picture] FROM <\/span>[dbo].[Categories] AS <\/span>[t0]\r\nWhere EXISTS<\/span>(\r\nSelect NULL AS <\/span>[EMPTY] FROM <\/span>[dbo].[Products] AS <\/span>[t1]\r\nWhere <\/span>([t1].[Discontinued] = 1) AND\r\n<\/span>([t1].[CategoryID] = [t0].[CategoryID])\r\n)<\/pre>\n
All<\/h1>\n
\u8bf4\u660e\uff1a\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u6240\u6709\u5143\u7d20\u662f\u5426\u90fd\u6ee1\u8db3\u67d0\u4e00\u6761\u4ef6\uff1b\u4e0d\u5ef6\u8fdf<\/p>\n
1.\u5e26\u6761\u4ef6\u5f62\u5f0f<\/h2>\n
var <\/span>q =\r\nfrom <\/span>c in <\/span>db.Customers\r\nwhere <\/span>c.Orders.All(o => o.ShipCity == c.City)\r\nselect <\/span>c;<\/pre>\n
Contains<\/h1>\n
\u8bf4\u660e\uff1a\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u662f\u5426\u5305\u542b\u6709\u67d0\u4e00\u5143\u7d20\uff1b\u4e0d\u5ef6\u8fdf\u3002\u5b83\u662f\u5bf9\u4e24\u4e2a\u5e8f\u5217\u8fdb\u884c\u8fde\u63a5\u64cd\u4f5c\u7684\u3002<\/p>\n
string<\/span>[] customerID_Set =\r\nnew string<\/span>[] { "AROUT"<\/span>, "BOLID"<\/span>, "FISSA" <\/span>};\r\nvar <\/span>q = (\r\nfrom <\/span>o in <\/span>db.Orders\r\nwhere <\/span>customerID_Set.Contains(o.CustomerID)\r\nselect <\/span>o).ToList();<\/pre>\n
\u8bed\u53e5\u63cf\u8ff0\uff1a\u67e5\u627e"AROUT", "BOLID" \u548c "FISSA" \u8fd9\u4e09\u4e2a\u5ba2\u6237\u7684\u8ba2\u5355\u3002\u5148\u5b9a\u4e49\u4e86\u4e00\u4e2a\u6570\u7ec4\uff0c\u5728LINQ to SQL\u4e2d\u4f7f\u7528Contains\uff0c\u6570\u7ec4\u4e2d\u5305\u542b\u4e86\u6240\u6709\u7684CustomerID\uff0c\u5373\u8fd4\u56de\u7ed3\u679c\u4e2d\uff0c\u6240\u6709\u7684CustomerID\u90fd\u5728\u8fd9\u4e2a\u96c6\u5408\u5185\u3002\u4e5f\u5c31\u662fin\u3002 \u4f60\u4e5f\u53ef\u4ee5\u628a\u6570\u7ec4\u7684\u5b9a\u4e49\u653e\u5728LINQ to SQL\u8bed\u53e5\u91cc\u3002\u6bd4\u5982\uff1a<\/p>\n
var <\/span>q = (\r\nfrom <\/span>o in <\/span>db.Orders\r\nwhere <\/span>(\r\nnew string<\/span>[] { "AROUT"<\/span>, "BOLID"<\/span>, "FISSA" <\/span>})\r\n.Contains(o.CustomerID)\r\nselect <\/span>o).ToList();<\/pre>\n
Not Contains\u5219\u53d6\u53cd\uff1a<\/p>\n
var <\/span>q = (\r\nfrom <\/span>o in <\/span>db.Orders\r\nwhere <\/span>!(\r\nnew string<\/span>[] { "AROUT"<\/span>, "BOLID"<\/span>, "FISSA" <\/span>})\r\n.Contains(o.CustomerID)\r\nselect <\/span>o).ToList();<\/pre>\n
1.\u5305\u542b\u4e00\u4e2a\u5bf9\u8c61\uff1a<\/h2>\n
var <\/span>order = (from <\/span>o in <\/span>db.Orders\r\nwhere <\/span>o.OrderID == 10248\r\nselect <\/span>o).First();\r\nvar <\/span>q = db.Customers.Where(p => p.Orders.Contains(order)).ToList();\r\nforeach <\/span>(var <\/span>cust in <\/span>q)\r\n{\r\nforeach <\/span>(var <\/span>ord in <\/span>cust.Orders)\r\n{\r\n\/\/do something\r\n<\/span>}\r\n}<\/pre>\n
2.\u5305\u542b\u591a\u4e2a\u503c\uff1a<\/h2>\n
string<\/span>[] cities =\r\nnew string<\/span>[] { "Seattle"<\/span>, "London"<\/span>, "Vancouver"<\/span>, "Paris" <\/span>};\r\nvar <\/span>q = db.Customers.Where(p=>cities.Contains(p.City)).ToList();<\/pre>\n
\u603b\u7ed3\u4e00\u4e0b\u8fd9\u7bc7\u6211\u4eec\u8bf4\u660e\u4e86\u4ee5\u4e0b\u8bed\u53e5\uff1a<\/p>\n\n\n\n\n\n\n
Group By\/Having<\/td>\n\u5206\u7ec4\u6570\u636e\uff1b\u5ef6\u8fdf<\/td>\n<\/tr>\n
Any<\/td>\n\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u662f\u5426\u6709\u5143\u7d20\u6ee1\u8db3\u67d0\u4e00\u6761\u4ef6\uff1b\u4e0d\u5ef6\u8fdf<\/td>\n<\/tr>\n
All<\/td>\n\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u6240\u6709\u5143\u7d20\u662f\u5426\u90fd\u6ee1\u8db3\u67d0\u4e00\u6761\u4ef6\uff1b\u4e0d\u5ef6\u8fdf<\/td>\n<\/tr>\n
Contains<\/td>\n\u7528\u4e8e\u5224\u65ad\u96c6\u5408\u4e2d\u662f\u5426\u5305\u542b\u6709\u67d0\u4e00\u5143\u7d20\uff1b\u4e0d\u5ef6\u8fdf<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n","protected":false},"excerpt":{"rendered":"
Group By\/Having\u64cd\u4f5c\u7b26 \u9002\u7528\u573a\u666f\uff1a\u5206\u7ec4\u6570\u636e\uff0c\u4e3a\u6211\u4eec\u67e5\u627e...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13],"tags":[],"class_list":["post-126","post","type-post","status-publish","format-standard","hentry","category-NET"],"_links":{"self":[{"href":"https:\/\/www.poloo.org\/index.php?rest_route=\/wp\/v2\/posts\/126","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.poloo.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.poloo.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.poloo.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.poloo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=126"}],"version-history":[{"count":0,"href":"https:\/\/www.poloo.org\/index.php?rest_route=\/wp\/v2\/posts\/126\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.poloo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=126"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.poloo.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=126"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.poloo.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=126"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}