Programmer Group

summary on must be used with join SQL1 finds all the information of the latest employee select*from employees order by hire_date desc limit 1; select * from employees where hire_date = (select max(hire_date) from employees); ORDER BY sorts the result set according to the specified column. By default, ORDER BY DESC is in ascending ...

analysis ● 1. Observe and run for at least one day to see the slow production ● 2. Start the slow query log, set the threshold value, for example, slow SQL is more than 5 seconds, and grab it ● 3.explain + slow SQL analysis ● 4.show profile ● 5. Optimize the parameters of SQL database server (O & M or DBA) summary ● 1. Enable and capture ...

MyBatis framework dynamic Sql Dynamic SQL: judge the conditions through various tags provided by MyBatis to realize dynamic splicing of SQL statements. The expression used for conditional judgment here is OGNL expression. The commonly used dynamic SQL tags are,,, and so on. The dynamic SQL statement of MyBatis is very similar to the stat ...

1. Course introduction first day: 1.Oracle concept and installation 2. Basic query 3. Condition query 4. Functions in Oracle the second day: 1. Multi table query (mysql also has the same concept, different syntax and important aspect) 2. Sub query (it also exists in mysql, with the same concept, different syntax and important aspect) on th ...

introduction With the rapid development of office automation and e-commerce, enterprises rely more and more on information system. Database, as the core of information system, plays an important role. Database backup is an important means to recover important data in time and prevent data loss in case of data loss. A reasonable database ...

Oracle create table Oracle table is the core of Oracle database and the logical basis for storing data. Oracle table is a two-dimensional data structure. The data with column fields and corresponding columns constitute a data storage structure. You can simply look at a two-dimensional table in rows and columns. Columns represent Oracle columns ...

Chapter 56 SQL command INSERT OR UPDATE Add a new row to the table or update an existing row in the table. outline INSERT OR UPDATE [%keyword] [INTO] table SET column = scalar-expression {,column2 = scalar-expression2} ... | [ (column{,column2} ...) ] VALUES (scalar-expression {,scalar-expression2} ...) | ...

Variable parameters The location of method parameters in java supports one syntax Method name ([type]... Variable name) The above expression is variable parameter //Declare a method with variable parameters public void sum(int... nums){ //Parameter... Indicates that the variables specified by this parameter are processed as an array ...

Chapter 55 SQL command INSERT (4) Embedded SQL and dynamic SQL examples The following embedded SQL example creates a new table SQLUser.MyKids. The following example uses INSERT to populate this table with data. After inserting the sample, an example of deleting SQLUser.MyKids is provided. ClassMethod Insert2() { &sql( CREA ...

2021SC@SDUSC Continue the analysis of AbstractSQLConfig last week. The following code is @ override @Override public boolean isExplain() { return explain; } @Override public AbstractSQLConfig setExplain(boolean explain) { this.explain = explain; return this; } @Override public List<Join> getJoinList() { return joinList ...