Programmer Group

1, Index overview 1. Introduction An index is a structure that sorts the values of one or more columns in a database table. Using an index can quickly access specific information in a database table. For example, index: if a certain page in the database is regarded as a book, the index is like a book directory. You can quickly find the locat ...

1, Hive's architecture design and SQL statement review summary 1.1. Data warehouse The definition put forward by Bill Inmon, the father of data warehouse, in his book "Building the Data Warehouse" published in 1991 is widely accepted. (DW for short) (DM) Data Warehouse is a Subject Oriented, Integrated, non volatile and Time V ...

Use the SELECT statement for basic queries in the studentsdb database. (1) In the student_info table, query each student's school number, name, birth date information. SELECT School Number,Full name,Date of birth FROM `student_info`; (2) Query the names and home addresses of students whose student_info form number is 0002. SELECT Full name ...

Hello, I'm the elder brother of Chinese menong green tea. Welcome to my personal WeChat official account: 8 Kangyuan road! Mybatis-demo 1. Explanation of professional terms 1.1 Dao Dao layer is called data access layer and persistence layer, and its full name is Data access object. It is a kind of bottom-level and basic operation. It is sp ...

1, Column attribute problem auto_ The increment dimension must be a primary key When creating a table, once you use auto_ For the increment description field, after a single piece of data corresponding to the primary key field is deleted, no data can be added to the corresponding content of this primary key field. As shown in the following f ...

Database and table building --Build database create database test; --Build table create table student(s_id string,s_name string,s_birth string,s_sex string) row format delimited fields terminated by '\t'; create table course(c_id string,c_name string,t_id string) row format delimited fields terminated by '\t'; create table teacher(t_id string ...

JDBC core knowledge points 1. What is JDBC? JDBC is a set of specifications proposed by SUN company, which provides unified access to a variety of relational databases. 2. What are the components of JDBC? JDBC is composed of a set of interfaces proposed by SUN company and implementation classes (driver jars) provided by various database man ...

1, Data We talked about the log before the database drop. Today, it's very troublesome to analyze the data drop. But the principle is the same. In the previous analysis, we can clearly know that in MySql, no matter what kind of data, it enters the cache first, and then drops the disk to save. In the database, what is the most important? Of cou ...

Original website: JPA--SpringBoot -- custom SQL -- Integration / method / how / how / instance / example / actual combat / tutorial -- spring data JPA_ CSDN blog brief introduction explain         When JPA customizes SQL, all additions, deletions and queries are annotated with @ Query, except that the statements inside a ...

0. Test data set and description 0.1 preparation of test data [test data 1] WITH Temp1 AS ( SELECT 'Zhang San' AS Name, 'chinese' AS Subject, one hundred AS Scores UNION ALL SELECT 'Zhang San' AS Name, 'mathematics' AS Subject, ninety AS Scores UNION ALL SELECT 'Zhang San' AS Name, 'English' AS Subject, eighty AS Scores UNION ALL SELECT 'Li ...