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again: "If I only have name is not NULL, then this SQL does not become the update set name = #{name}, where ...?" The comma behind your name will cause an error! ”Yes, at this time, you can use MyBatis to provide us with the set tag. The following is modified by the set label: This trim can be expressed as:Where is the prefixoverrides (prefix) used, set is the use of the suffixoverrides (suffix), see it!5. Foreach: You have for, I have foreach, don't think just you dick!There is a for in

, 3);Select mid (' ABCDEFG ', 2,2);(13) function to match the starting position of a substringLOCATE (STR1,STR),POSITION (str1 in str2) and INSTR (STR,STR1) 3 functions are the same. Returns the starting position of the substring str1 in the string strSelect locate (' Ball ', ' football '), position (' ball ' in ' Football '), InStr (' Football ', ' Ball ');(14) Inverse string function reverse (s)Select reverse (' 12345 ');(15) Returns a string function at the specified positionELN (N, string 1,

ImportOrg.apache.log4j.Logger;4 5 ImportCom.mongodb.BasicDBObject;6 ImportCom.mongodb.DBObject;7 8 Public classMain {9 Ten Public Static voidMain (string[] args) { OneLogger Logger = Logger.getlogger (Main.class); A - for(inti = 0; i ) { -DBObject Bson =NewBasicdbobject (); theBson.put ("name", "Ryan" +i); - Logger.debug (Bson); - } - } +}Main.java6, in step 5, we performed 10 million log insertions, the data structure is as follows:The defaul

replicate.　　　　　　(4) View the user table on Maste select * from Mysql.user \g, see a more of the user we just specified, see the reppc:y of this record, that the user has the rights to copyAt this point, Master has been configured OK, check the status: Show Master status;　　　　(5) Restart slave first:　　　　(6) View salve status show slave status:　　　　Slave-io-running:yes,slave-sql-running:yes appears, the master-slave configuration succeeds!Five. Testing(1) Add a new record in the student table in Ma

points small there is a mistake, the whole is still satisfactory. But I don't know if you remember what I said before, K-means has a priori condition that the data satisfies the Gaussian distribution of the same variance, so we deliberately make the variance of the data to see if the clustering effect will be greatly affected.#方差不等数据data2, Y2=ds.make_blobs (n,centers=centers,cluster_std= (2,2,5,8), random_state=0) Plt.scatter (data2[:,0], DATA2[:,1],C=Y2,CMAP=CM) plt.title (U ' raw data distrib

length exceeds maxframelength, immediately report the toolongframeexception exception, false, read the entire frame and then report the exception */P Ublic customdecoder (int maxframelength, int lengthfieldoffset, int lengthfieldlength, int lengthadjustment, int Initialbytestostrip, Boolean failFast) {super (maxframelength, Lengthfieldoffset, Lengthfieldlength, Lengthadjustment, Initialbytesto Strip, FailFast); } @Override protected Object decode (Channelhandlercontext ctx, bytebuf in) thro

parameters of the fixed MessageBox.Show method, using it to pop up the dialog, the alert method implementation is very simple, just need the following sentence code:　　MessageBox.Show (null, message," informational hint ", messageboxbuttons.ok,messageboxicon.information);Where the message is a parameter accepted by the alert method.In 3 button click events, the program code to implement the corresponding data update operations, these operations are explained in detail before, here is no longer m

SELECT AVG (DISTINCT as avg_price from dbo.) Products WHERE='DLL01'; -- because the DISTINCT parameter is used, the average value only takes into account the various prices 　　"Attention" DISTINCT cannot be used for count (*), but can be used for count (column)　　the hint is available for MIN () and MAX (), but it has no real value 9.3 combined aggregate function select count (* ) as Num_items, min (prod_price) as Price_min, Span style= "color: #ff00ff;" >max (prod_price) as

UDFs are similar to stored procedures, where a user-defined function is an ordered set of T-SQL statements that are pre-optimized and compiled, and can be used as a unit to test calls. The main difference between UDFs and stored procedures is the way the results are returned, and in order to support more return values, UDFs are more restrictive than stored procedures.UDF basic syntax: CREATE FUNCTION RETURNS As Begin/* code */ENDThe simplest thing to try is a UDF:CREATE FUNCTION Fun_getdatediff

UDFs are similar to stored procedures, where a user-defined function is an ordered set of T-SQL statements that are pre-optimized and compiled, and can be used as a unit to test calls. The main difference between UDFs and stored procedures is the way the results are returned, and in order to support more return values, UDFs are more restrictive than stored procedures.UDF basic syntax: CREATE FUNCTION RETURNS As Begin/* code */ENDThe simplest thing to try is a UDF:CREATE FUNCTIONFun_getdatediff (

through select execution. In order to avoid = is treated as a relational operator at this time, use: = instead. (The Set statement can use = and: =). Select @var: =; Select @v1: =id, @v2=name from T1 limit 1; Select * from Tbl_name where @var: =; Select into can assign data from a query in a table to a variable. -| Select Max (height) into @max_height from TB; --Custom variable name to avoid a user-defined variable in a SELECT statement that conflicts with a system identifier (usually a

achieve mutual exclusion by locking a specific area of a file. SQLite mainly contains 4 kinds of locks, shared_lock (Shared Lock), (reserved_lock) reserved lock, (Pending_lock) pending lock and (Exclusive_lock) exclusive lock, where shared lock and exclusive lock in the same area of the file. Reserved_lock is mainly used to write and write mutually exclusive, Pending_lock is mainly used for reading and writing mutual exclusion, and has the effect of delaying mutual exclusion. About the lock con

, has been introduced mariadb; Column Storage Engine: Infobright: Currently more famous column engine, suitable for Yu Hai volume data storage scenarios, such as PB level, designed for data analysis and data warehouse design; Infinidb MonetDB Luciddb 10. Open Source Community Storage engine Aria: Formerly Maria, can be understood as an enhanced version of MyISAM (support for post-crash security recovery, support data caching); Groona: Full-text indexin

MongoDB projection means to select only the necessary data instead of selecting the entire data for a file. If a document has 5 fields, you need to display only 3, and then select only 3 fields.Find () methodMongoDB's Find () method, which is interpreted in the MongoDB query document, accepts the second optional parameter that is the list of fields to retrieve. In MongoDB, when the Find () method is executed, it displays all fields of a document. To limit this, you need to set the field List val

: set transaction read only; For example, there are two user system, Scott each with Sqlplus Landing, operation as follows: The first step: Use the System user login Sqlplus, set the read-only transaction. sql> SET transaction read only; Transaction set. Step two: Log in sqlplus with the Scott user, as follows: Sql> Select COUNT (*) from EMP;--Query the total number of records for the EMP table COUNT (*) -------- -- sql> INSERT INTO EMP values (7777, ' Zhangsan ', ' MANAGER ',

Label:1. Use of indexes --Create a table Create TableT_user (Idint Primary Key Identity(1,1), UNonvarchar(Ten), UNamenvarchar(Ten), Uageint ) --Create an index (to index a field uname) Create IndexIdx_user_name onT_user (UName)--Delete Index Drop IndexIdx_user_name onT_user 2. What is an index Index is a data structure that helps MSSQL efficiently get 3. Why use an index A. Uniqueness of the index, which guarantees the uniqueness of each row of data B. Greatly accelerate the speed of data re

3select* fromdba_sourceunion 4select*fromdba_ sourceunion 5select*fromdba_sourceunion 6select*fromdba_sourceunion 7 select*fromdba_sourceunion 8select *fromdba_sourceunion 9select*from dba_sourceunion 10select*fromdba_sourceunion 11select*fromdba_source); sql> shutdown Abort ORACLE instance shut down.5. We'll go to the 11GRAC1 and see the results of step 3rd.Sql> Select Inst_id,sid from gv$session where username= ' SCOTT '; inst_id SID -------------------- 1 64Scott's connection has shifted f

": 1}, "shard0001": {"ns": "Test.kk", "Count": 32852, "size": 3679424, "avgobjsize": "Numextents" : 6, "storagesize": 11182080, "lastextentsize": 8388608, "Paddingfactor": 1, "paddingfactornote": "Padding Factor is unused and unmaintained in 3.0. It remains hard coded to 1.0 for compatibility only. "," userflags ": 1," capped ": false," nindexes ": 2," tot Alindexsize ": 3343984," indexsizes ": {" _id_ ": 1389920," id_hashed ": 1954064}," OK ": 1}," Shar D0002 ": {" ns ":" Test.kk "," Count ":

statement is used to delete the index "commodity _index" in the "commodity information" of the Database "reseller". If you want to delete an index, but cannot determine whether the index exists, you can also add a simple judgment statement to judge first. For example, delete the "Customer Information sheet _index" index in the "Customer information sheet" of the Database "reseller". 5. Learning Summary As for the learning summary of this chapter of the index, I feel that I have learned a

datasource. It exists between the data source and the business layer, encapsulating the details of access to the data, such as database connections, sending execution SQL statements, and closing the connection resources. The primary purpose of DAO is to completely separate the underlying data access operations from the high-level business logic operations, providing transparent data access services to the business layer and enhancing the flexibility of the program. The DAO component encapsulate