Can't this data be read? - Codes Helper - Programming Question Answer

Can't this data be read?

use lyb;

< table > < thead > < tr > < th > show tables; < / th > < / tr > < / thead > < tbody > < tr > < td > Tables_in_lyb < / td > < / tr > < tr > < td > _ link < / td > < / tr > < tr > < td > admin < / td > < / tr > < tr > < td > author < / td > < / tr > < tr > < td > cart < / td > < / tr > < tr > < td > city < / td > < / tr > < tr > < td > link < / td > < / tr > < tr > < td > lyb < / td > < / tr > < tr > < td > lyb1 < / td > < / tr > < tr > < td > messages < / td > < / tr > < tr > < td > news < / td > < / tr > < tr > < td > province < / td > < / tr > < tr > < td > route < / td > < / tr > < tr > < td > shop < / td > < / tr > < / tbody > < / table >

13 rows in set (0.00 sec)

MariaDB [lyb] > select * from link;
ERROR 1932 (42S02): Table "lyb.link" doesn"t exist in engine

in this database file, there are

ls / var/lib/mysql/lyb
admin.frm city.frm link.frm lyb1.frm messages.MYD province.frm
author.frm db.opt link.MYD lyb.frm messages.MYI route.frm
cart.frm _ link.frm link.MYI messages.frm news.frm shop.frm

Jun.04,2021

in ORACLE, field names or table names can begin with an underscore, but they must be enclosed in double quotation marks. It's a bit weird to try not to start with an underscore.

example:

SQL > create table T1 (_ col1 number,_col2 number);

create table T1 (_ col1 number,_col2 number)

invalid ORA-00911: characters

SQL > create table T1 ("_ col1" number, "_ col2" number);

Table created

Previous: Is it because the array is treated as a pointer that the cPP array does not report an error when it is out of bounds?

Next: Chai syntax expect ([2]) .to.be.grammar ([2]) Why failed?

Php mariadb sum divided by if there is no value, can NAN, be shown as 0?
$selectTip = $pdo->query("SELECT * FROM `tips_rate` WHERE `tip_id` = ".$row[ id ]." " ); $selecttotal = mysqli_num_rows($selectTip); $rate = $pdo->query("SELEC...

Mysqli mariadb php

Feb.26,2021
What is the relationship between transactions at different levels of isolation?
for example, the isolation level of transaction An is repeatable read my understanding is that a read sql statement of transaction An is the same as the result repeated many times, regardless of whether or not other transactions have changed the data ...

Database mysql

Feb.26,2021
About the problem of the sudden downmachine of the mysql master from one of the parties.
I know that mysql master and slave have been configured, but I don t know what to do if one of them dies: 1. If there is only one master and one slave, do you want to upgrade the master manually in case the master dies? (it seems that you can t call...

Read-write-separation master-slave-backup master-slave-replication mysql

Feb.26,2021
SQL statement, JOIN multiple table join table query problem
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...

Mysql sql

Feb.26,2021
Check-in function, data storage time, year, month, day, why use varchar
do a check-in function `create_time` decimal(20,3) NOT NULL, `create_date_ymd` varchar(15) NOT NULL COMMENT , `create_date_ym` varchar(15) NOT NULL, `create_date_y` int(4) NOT NULL, `create_date_m` int(2) NOT NULL, `create_date_d` int(2) ...

Php mysql

Feb.26,2021
Mysql fetches segmented data before the current time
as shown in the following figure the current time is 16 41 00. I want to take this section of data every two hours. How should sql write ? ...

Mysql

Feb.27,2021
How mysql queries specified data in multiple tables
1. Problem description assume that there are n game order tables in the database, and the table name is game_ [0-9a-z] + _ order. . It is known that there is an order number 18demo000001. How can we efficiently find out which game table this order is i...

Mysql

Feb.27,2021
The optimization problem of group by sentence in mysql and how to find the train of thought
I want to optimize a sentence about group by. I don t know where to start. I want to find a train of thought . SELECT adv_id, network_id, SUM(re_click) AS clk, SUM(deny_click) AS dny_clk, SUM(re_conver) AS re_ins, SUM(mat_conver) AS mat_ins, SUM(def_...

Mysql php

Feb.27,2021
On the Database query Optimization of java programmers in interview
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...

Oracle mysql sql java

Feb.27,2021
Does mysql support whether the query condition is an object?
like this SELECT * FROM material WHERE {key:value} limit 1 ...

Axios node.js express php mysql

Feb.27,2021
MySQL statement to ask for help
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. ...

Sql mysql

Feb.27,2021
The problem of computing sorting in mysql query
check-in table: fields include user id userid check-in time signtime timestamp type int check-in type type is divided into 0 and 1 for check-in and check-out, respectively. A user can sign twice a day, once check-in and one check-out. Check-in and ch...

Mysql

Feb.27,2021
Why can I still insert null values when not null, is set in mysql?
Table structure ...

Mysql

Feb.27,2021
Annotation invalidation of dao interface using mybatis @ CacheNamespace cache
use mybatis to configure custom secondary cache. Using xml annotation can use < cache type= "com.test.dao.MybatisRedisCache " > to successfully use custom cache, but using @ CacheNamespace (implementation = MybatisRedisCache.class) on the dao i...

Java spring mybatis redis mysql

Feb.27,2021
The correct limit and take in the Larave with () function
class essay extends Model { public function comment() { return $this->hasMany( App comment ) } } class comment extends Model { public function essay() { return $this->belongsTo( App essay ) } } ...

Mysql laravel

Feb.27,2021
The time-consuming problem of batch storage of a large amount of data in Mysql:, why does the speed decline so fast when the amount of data is large?
mybatis+mysql for java projects int batchAmount = 20000; for (int startIndex = 0; startIndex < size; startIndex += batchAmount) { int endIndex = startIndex + batchAmount; endIndex = (endIndex &...

Mysql java

Feb.27,2021
Mysql master-slave server, master database build table slave database not Synchronize
Master and Slave built by mysql5.6, the newly created table is not backed up to the slave library master and slvae data can both correspond to can t the test library be automatically backed up to the slave library when establishing a master-slav...

Linux mysql

Feb.27,2021
PHP MYSQL loops to output a single piece of data sequentially
I want to do a circular sequence to output pictures. Don t know how to write this code? Table structure for example, now the field ID of key=1 is 1, 2, 5, 7, 10, 11, 6 fields I want to output one at a time in order. output id 1 field for t...

Php mysql

Feb.27,2021
Is it convenient to modify data items when there is a lot of data in the mysql enum type?
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? ...

Mysql sql

Feb.28,2021
Please help me convert this native SQL statement into TP5 thank you!
ask God to help me translate this native SQL statement into TP5 thank you! It is Db:: ( name )-> this kind of chained operation select a.id, a.titlerect a. Createwriting time as answer_count from fa_question a. Isometric solvepaper count (b.qid) as ...

Thinkphp5 mysql php

Feb.28,2021

Menu