learning sql o reilly

to be completely isolated, a bit of concurrency ...). Therefore, SQL Server's default read commited is a good choice to strike a balance between isolation and concurrency.SQL Server passes the lock, just like a traffic light at a crossroads, to tell all concurrent connections that at the same time those resources can be read and those resources can be modified. As mentioned earlier, the query itself is not a gentleman, so it needs to be supervised. W

Label:Stored procedures: SQL Server Stored Procedures Blog Park on an article, explained in very detailed, there are test code, very practical. Execute dynamic SQL statements in SQL Server stored procedures The curse and blessings of the dynamically SQL stored procedures and Cursors

Label:1.DISTINCT DISTINCT This keyword is used to filter out redundant duplicate records to keep only one, but it is often used only to return the number of distinct records, rather than using it to return all values that are not re-recorded. The reason is that distinct only with double-loop query to solve, and so for a very large number of stations, will undoubtedly directly affect the efficiency. The 2.ORDER by order BY statement is used to sort the result set based on the specified column. T

Label:1.Top Query Statements SELECT TOP n Used to get the number of data bars returned by the rule. SELECT TOP N PERCENT 2.LIKE operator Query the records in the database by using a wildcard character. _ Denotes matching with any single character % indicates a match to a string containing one or more characters [] matches any single character in a specific range (for example, [a-f]) or a specific set (for example, [abcdef]). [^] or [!] Matches any single character other than a specific range (

table As a table example select E.emono,e.ename from (SELECT * from where deptno=30) E gave the table an alias E As a condition there are several situations Single-column: You can use =,>, A multiline column (collection) can be Single-row multi-column (object) is a row, like an object, what property has Multiline multiple columns: Multiple rows and columns are always used as tables from behind Single-row Example: SELECT * from emp where sal > (select

(cp.qty,0), NVL (fp.qty,0), Cast (Decode (TAB1.QTY*100,0,0,NVL (tab1.qty,0)/tmm. FQTY*100) as number (18,2)), Cast (Decode (TMM). fqty*100,0,0,100-tbh.fgoodrates-(NVL (bp.qty,0)/tmm. fqty*100+ NVL (cp.qty,0)/tmm. FQTY*100+NVL (fp.qty,0)/tmm. FQTY*100)) as number (18,2)), To_char (TMM. Fcreatetime, ' Yyyy-mm-dd '), To_char (Add_months (TMM. fcreatetime,1), ' Yyyy-mm-dd '), Cbc.cfparticlecount, T5.SL, T6.SL, Case when To_char (Add_months (TMM. fcreatetime,1), ' Yyyy-mm-dd ') , Decode (Tmm.fbasest

Tags: search command LandingMONGO 192.168.0.134:27017 View GalleryShow DBS Building a libraryUse testDb.createcollections ("command") To view a table in a libraryShow collections; Insert statementDb.command.insert ({name: "SSH", decriptions: "This is login Remote host command"})Db.command.insert ({name: "Ifconfig", Decriptions: "It can search for IP"})Db.user.insert ({name: "Zhangsan", Age: "20"})Db.user.insert ({name: "Lisi", Age: "21"})Db.user.insert ({name: "Zhaowu", Age: "30"})Db

), -)+'1') --3. The first or last day of the month in which the specified date is located --A. First day of the monthSelectconvert (datetime,CONVERT(Char(8),@dt, -)+'1') --B. The last day of the monthSelectdateadd ( Day,-1,CONVERT(Char(8),DATEADD(Month,1,@dt), -)+'1') --C. Last day of the month (easy-to-use error method)Selectdateadd (Month,1,DATEADD( Day,- Day(@dt),@dt)) --4. Any day of the week on which the specified date is locatedSelectdateadd ( Day,@number-DATEPART(Weekday,@d

privatesqlsessionsqlsession;private persondaopersondao;privateloggerlog= logger.getlogger (junittest.class); @Before publicvoidsetup () throwsException{ sqlsession=sqlsessionfactoryutil.opensession (); persondao=sqlsession.getmapper (Persondao.class);} @After publicvoidteardown () throws Exception{sqlsession.close (); } @Test publicvoidfinduser () { Map additions and deletions are returned by the affected line number /***by usage */@ Testpublicvoidfinduser2 () { Map Where Usage

unique (name)4. Invalidating a constraintThe Emp3 table has a unique constraint that invalidates it, but does not deletesql> ALTER TABLE Emp3 2 disable constraint emp3_email_uk;5. Effective, if the data of the column should conform to the constraints of the constrained constraint, such as the unique constraint, in order to be effective, it is necessary to ensure that the data of this column cannot be duplicated.sql> ALTER TABLE Emp3 2 enable constraint Emp3_email_uk; 6. Query constraintsSEL

results of multiple SELECT statements together, in which case it is necessary to combine the results of several SELECT statements, for example, to query all the employee information of company A and Company B, and then merge the results of the two queries together. The Union and UNION ALL keywords are used for the merge operation. Format: SELECT statement 1 UNION | UNION All SELECT statement 2 UNION | UNION All ............ Example: Query the value of the d_id field from the Department table a

usingSystem;usingSystem.Data.SqlClient;namespaceconsoleapplication{classProgram {Static voidMain (string[] args) {SqlConnection con=NewSqlConnection ("Server=.\\sqlexpress;uid=sa;pwd=123456;database=studb"); Con. Open (); SqlCommand com=con. CreateCommand (); Com.commandtext="SELECT * from Stuinfo"; SqlDataReader Reader=com. ExecuteReader (); while(reader. Read ()) Console.WriteLine (reader["Stuname"]. ToString () + reader["Stuage"]. ToString () + reader["Stusex