Linq to SQL Like Operator(×ªÔØ)
As a response for customer's question, I decided to write about using Like Operator in Linq to SQL queries.
Starting from a simple query from Northwind Database;
var query = from c in ctx.Customers
where c.City == "London"
select c;
The query that will be sent to the database will be:
SELECT CustomerID, CompanyName, ...
from dbo.Customers
WHERE City = [London]
There are some ways to write a Linq query that reaults in using Like Operator in the SQL statement:
1. Using String.StartsWith or String.Endswith
Writing the following query:
var query = from c in ctx.Customers
where c.City.StartsWith("Lo")
select c;
will generate this SQL statement:
SELECT CustomerID, CompanyName, ...
from dbo.Customers
WHERE City LIKE [Lo%]
which is exactly what we wanted. Same goes with String.EndsWith.
But, what is we want to query the customer with city name like "L_n%"? (starts with a Capital 'L', than some character, than 'n' and than the rest of the name). Using the query
var query = from c in ctx.Customers
where c.City.StartsWith("L") && c.City.Contains("n")
select c;
generates the statement:
SELECT CustomerID, CompanyName, ...
from dbo.Customers
WHERE City LIKE [L%]
AND City LIKE [%n%]
which is not exactly what we wanted, and a little more complicated as well.
2. Using SqlMethods.Like method
Digging into System.Data.Linq.SqlClient namespace, I found a little helper class called SqlMethods, which can be very usefull in such scenarios. SqlMethods
Ïà¹ØÎĵµ£º
ÉÁ»Ø
1 ÌØÕ÷
ÉÁ»ØÊý¾Ý¿âÖ»ÊÇÂß¼Êý¾ÝÔâµ½ÆÆ»µÊ±µÄÊֶΡ£
ÉÁ»ØÊý¾Ý¿âÈÕÖ¾±ØÐëÔÚÊý¾Ý¿â»Ö¸´ÇøÖд´½¨¡£
ÉÁ»ØÈÕÖ¾²»ÐèÒª¹éµµ£¬²»ÄÜÓÃÓÚÎïÀí»Ö¸´¡£
Ö´ÐÐÉÁ»ØÊý¾Ý¿â²Ù×÷ʱ£¬±³¾°½ø³ÌRVWR¾ÍÆô¶¯ÁË¡£
2 ʹÓÃÉÁ»ØÊý¾Ý¿â
3ÖÖ¹¤¾ß£¬SQL*Plus£¬RMAN£¬OEM¡£
£¨1£©ÒªÇó
ΪÁËʹÓÃÉÁ»ØÊý¾Ý¿â£¬Êý¾Ý¿â±ØÐë´¦Óڹ鵵ÈÕ־ģʽ¡ ......
1.¼¯ºÏ²Ù×÷
ѧϰoracle
Öм¯ºÏ²Ù×÷µÄÓйØÓï¾ä£¬
ÕÆÎÕunion,union
all,minus,interestµÄʹÓÃ,Äܹ»ÃèÊö½áºÏÔËË㣬²¢ÇÒÄܹ»½«¶à¸ö²éѯ×éºÏµ½Ò»¸ö²éѯÖÐÈ¥£¬Äܹ»¿ØÖÆÐзµ»ØµÄ˳Ðò¡£
°üº¬¼¯ºÏÔËËãµÄ
²éѯ³ÆÎª¸´ºÏ²éѯ¡£¼û±í¸ñ1-1
±í1-1
Operator Returns &nb ......
SQLÓï¾äµÄ´¦Àí
ps£ºMSDNÕª
ÓÅ»¯ ÔÚ»ù´¡±íÉÏ£¨²»ÒýÓÃÊÓͼ»òÔ¶³Ì±í£©µÄ SELECT Óï¾ä:SELECT Óï¾äÊǷdzÌÐòÐÔµÄ,ÕâÒâζ×ÅÊý¾Ý¿â·þÎñÆ÷±ØÐë·ÖÎöÓï¾ä£¬ÒÔ¾ö¶¨ÌáÈ¡ËùÇëÇóÊý¾ÝµÄ×îÓÐЧ·½·¨
´¦ÀíÉÏÃæ²½ÖèµÄ×é¼þ³ÆÎª“²éѯÓÅ»¯Æ÷”£º
ÊäÈ룺²éѯ¡¢Êý¾Ý¿â·½°¸£¨±íºÍË÷ÒýµÄ¶¨Ò壩ÒÔ¼°Êý¾Ý¿âͳ¼ÆÐÅÏ¢
& ......
¡¾AUTOTRACE¡¿SQLÓÅ»¯µÄÖØÒª¹¤¾ß--AUTOTRACE
Ìáµ½SQLÓÅ»¯£¬²»Äܲ»ÌáAUTOTRACEµÄÇ¿´ó¹¦ÄÜ¡£Ê¹ÓÃÆðÀ´·Ç³£±ã½Ý£¬²»¹ýÔÚÊÇʹÓÃ֮ǰ£¬ÐèÒª×öһЩÅäÖõŤ×÷¡£¼òÒªµÄÃèÊöÒ»ÏÂÕâ¸ö¹ý³Ì£¬¹©Ã»ÓÐʹÓùýµÄÅóÓѲο¼¡£
1.ʹÓÃsysÓû§Ö´ÐÐplustrce½Å±¾
sys@ora10g> @?/sqlplus/admin/plustrce
sys@ora10g> drop role plustrace ......