there is a composite index A where B condition Backx does not take the index why why it has something to do with the order of its fields can you answer from the underlying b-tree principle of the index? ...
I am learning the database. Most of them look up the database on the Internet, and the contents are all the same . create table Student(Sno char(3) primary key not null, Sname char(8) not null, Ssex char(2) not ...
$courseDetail = M( course ) ->field( c.course_id,c.name,from_unixtime(c.time) as course_time,c.room_id,tu.teacher_id,tu.relname as teacher_name, tu.mobile as teacher_mobile,su.student_id,su.nickname as student_name,su.mobile as student_...
because batch update operations are always involved recently, I don t know if batch operations can be performed, so we can only update, one by one in the loop , so I d like to ask whether there is a sql statement in the sql database that enables updat...
there are two insert statements in the mysql trigger. How to implement the second inert with the result of the first insert DELIMITER $$ USE `nightclub`$$ DROP TRIGGER *!50032 IF EXISTS * `create_histroy_room_statuses`$$ CREATE *!50017 DEFIN...
this sql statement, under thinkphp5.17 tp there is another problem. My sql statement is executed incorrectly. I can t see the error statement in the tract panel or runtime log. I want to see what I did wrong and what I think. ...
I am using SSMS2017, this version (perhaps earlier version has) has a function, that is, after the cursor is punctuated to something (variable, field, table name, etc.), the same string nearby will be highlighted, such as figure: " " >> similar func...
have the following two sample tables order amount is equal to orderinfo price*count in the table, and each order has more than one item. how can I get the top 10 users with the total amount of orders through the SQL statement? add: each user m...
for example, if the database has a field type of enum ( axiomagementific database ), can you change this field to enum when there are millions of data in the database? will it be slow? ...
how does sql write from the database table to the display of the page? requirement: the first-level classification needs sorting, the first-level classification shows its subcategories, and the subcategories also need sorting. ...
background: 1. I am a java programmer 2. Recently interviewed for a senior development position 3. The previous project mainly used less oracle,mysql, and the companies interviewed basically used mysql s 4. I am weak in the database 5. Recently, I...
MySQL database, the navicat software code used is as follows INSERT INTO EMP (EMPNO,ENAME,JOB) VALUES (9999 Zhang Zero , Software engineer ); error message [SQL] INSERT INTO EMP (EMPNO,ENAME,JOB) VALUES (9999 Zhang Zero, "Software engineer ")...
subject table, which can be understood as a classification table. The course and source_book tables are associated with subject now use the subject table as the main table to query how many courses and books are under this category. query statemen...