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1. Multi table query: 1. Query syntax: select Column name list from Table name list where.... 2. Prepare sql Create department table CREATE TABLE dept( id INT PRIMARY KEY AUTO_INCREMENT, NAME VARCHAR(20) ); INSERT INTO dept (NAME) VALUES ('Development Department'),('Marketing Department'),('Finance Department'); Create employee tabl ...

multi-table queryMulti table query, also known as association query, refers to two or more tables completing the query operation together.Prerequisite: these tables queried together are related (one to one, one to many). There must be an associated field between them. This associated field may or may not have a foreign key. For example: employe ...

DML language Data operation language: Inserting: insert ing Modify: update Delete: delete 1, Insert statement Mode 1: Syntax: insert into table name (column name...) Values (value 1,...); Features: it supports inserting multiple rows and querying subsets SELECT * FROM beauty; 1. The type of the inserted value should be consistent or com ...

Chapter 15 stored procedures and functions MySQL supports stored procedures and functions from version 5.0. Stored procedures and functions can encapsulate complex SQL logic. Applications do not need to pay attention to the complex SQL logic inside stored procedures and functions, but simply call stored procedures and functions. Overview of s ...

MySQL UPDATE multi table Association update 1.MySQL can UPDATE data based on multi table query. For the UPDATE operation of multiple tables, you need to be careful. It is recommended to use the SELECT statement to query and verify whether the updated data is consistent with your expectations before updating. Build two tables, one for prod ...

SQL Statement Review 1.Data Definition Construct 1.1 Create table Construct 1.1.1 table creation statement create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8,2) ); ----------------------------------- create table r ( A1 D1, A2 D2, ... An,Dn, (integrity-constraint_k) ); 1 ...

Dynamic SQL introduce In the mapping file of Mybatis, our SQL is relatively simple. Sometimes when the business logic is complex, our SQL changes dynamically. At this time, our SQL can not meet the requirements in the previous study. The official document on dynamic SQL reference is described as follows: Previous problems Example of mult ...

Lock List Shared and Column Exclusive LocksIntent LockRecord LockGap lockNext-Key LockInsert Intent LockAUTO-INC lock This time we will only discuss and experiment with intent locks. Gap lock Gap locks are also index records of locks, locking values that do not exist in gaps. What is gap lock? Gap locks are locks on gaps between index rec ...

backgroundIn our daily development, one kind of data we will come into contact with is hierarchical data. What is tiered data? Business organization chart, content management category, RBAC permission management, product category, etc. These are hierarchical data. The following is the product category hierarchy of an e-store:In this paper, we w ...

Supplement 4 When the connection is closed by default, we will submit it automatically, Each rollback is rolled back to the previous submission Transfer operation without considering database transactions When we finished the first transaction, we committed. As a result, an exception occurred, resulting in a direct exit. The subsequent t ...