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Transfer from Explain MySQL data types in detail , the content is slightly modified. integer data type Number of bytes Signed minimum Signed maximum Unsigned minimum Unsigned maximum TINYINT 1 -128 127 0 255 SMALLINT 2 -32768 32767 0 65535 MEDIUMINT 3 -8388608 8388607 0 16777215 INT 4 -2147483648 2147483647 0 4294967295 BIGINT 8 ...

introduction In actual business development, data interaction between multiple tables is often involved. At this time, single table query can no longer meet complex business requirements, so multi table connection query is needed; Connection query is mainly divided into the following three types: Inner connection Equivalent connectionNon ...

premise Process multiple business modules at the same time. Multiple business modules may need to transfer data to each other or need synchronous control. Two entities need to communicate with each other and must have resources that can be shared. Files on disk: -- > IO processing is slow and out of sync. Application scenario of process co ...

trigger 1. Define trigger CREATE TRIGGER Syntax format CREATE TRIGGER <Trigger Name > {BEFORE | AFTER} <Trigger event> ON <Table name> REFERENCING NEW|OLD ROW AS<variable> FOR EACH {ROW | STATEMENT} [WHEN <Trigger condition>]<Trigger action body> When a specific system e ...

Multi table query classificationCategory 1: equivalent connection vs non equivalent connection1. Equivalent connectionSELECT employees.employee_id, employees.last_name, employees.department_id, departments.department_id, departments.location_id FROM employees, departments WHERE employees.department_id = departments.department_ ...

1, Questions for each course Use an SQL statement to query the student table and the names of students with more than 80 points in each course. Solution 1: having Idea: if the minimum course score is greater than 80 points, then all his course scores must be greater than 80 points! code implementation SELECT name FROM xuesheng GROUP BY n ...

How to understand progressive framework Progressive framework means that if you are developing a small application, you can use vue's core library for easy development. If you are developing a large application, you can add vue's plug-in library for development. In other words, it can be selected according to the size of the application, so as ...

Overview of Servlet event listener In the development of relationship, it is often necessary to monitor some events, such as mouse click events and key press events. At this time, you need to use event listener. There are several important components in the listener: (1) Event: a user action (2) Event source: the object that generated the ...

Comparison operator= <=> <> != < <= > >= The comparison operator is used to compare the operands on the left and right of the expression. If the comparison result is true, it will return 1, if the comparison result is false, it will return 0, and in other cases, it will return NULL.Comparison operators are often us ...

1. in and exists In is a hash connection between the outer table and the inner table, while exists is a loop loop loop for the outer table. Each loop loop loop queries the inner table. It has always been inaccurate to say that exists is more efficient than in. If the two tables of the query are of the same size, there is little difference b ...