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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.
...
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Mysql trigger
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...
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How does Mysql merge two tables
ask how to write the sql statement
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How do Mysql: select nonclustered index columns, clustered index columns, unindexed columns and * compare performance?
has always thought that index optimization is effective in where is useless in select but it seems that there is a performance difference between select nonclustered index columns, clustered index columns, unindexed columns and select *? ...
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MySQL writes queries and asks for help?
Table T_USER
T_ROLE
:
the following is the table creation and data script
drop table if exists T_USER;
CREATE TABLE T_USER(
USER_ID INT,
USER_NAME VARCHAR(25)
);
INSERT INTO T_USER VALUES(1, USER_A );
INSERT INTO T_USER VALUES(2, USER_B )...
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Regular expressions in MYSQL
in mysql, set a regular expression to filter strings ending in number select number from test where number REGEXP xxxxxxxxx . ...
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Mysql query statement
A
a_id a_title a_key a_desc a_pid
1 A A A 1
B
b_id b_title b_key b_desc b_pid
1 b 2
C
c_id c_title c_key c_desc c_pid
1
$title= Ctitile || ...
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Can I use System.nanoTime () as the primary key ID?
for stand-alone service, the primary key ID is a long integer, which needs to be non-continuous. For example, self-increment cannot be implemented because it is continuous. I thought of using System.nanoTime () to do ID, because I haven t practiced it...
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SQL query COUNT is slow.
query the COUNT of a sentence (1), JOIN IN has 4 tables. The total number of records is 3800, and it takes 43 seconds this is SQL:
select count(1) from (
SELECT a.id AS "id", a.batch_id AS "batchId", a.product_type AS "product...
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How to print data through curl?
my mysql database has two pieces of data
when I print_r, it looks like this:
[{"errno":"1","errstr":"2","errfile":"3","errline":"4"},{"errno":"12",...
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The usage of as in sql query statement;
is currently self-learning mysql,. When querying, sometimes you need to use as aliases, but after adding as aliases to the following two query statements, why is it incorrect?
1, select cat_id,goods_name,shop_price from goods where shop_price in (sele...
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A SQL sentence burns the brain logic problem-ask the boss for guidance
as shown in the figure: the fields that reply_article is " 69 " and reply_type is " 0 " and reply_aims_user is null are required.
then! Here s the point. Use the reply_id in the previous query field as the primary key to associate the ...
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Perform a second screening from the result set
as shown in the figure, this association query is different in that it is associated with the same table
indicates that table_test
requirement: first query the result set of the field whose reply_type is 0, and then use the reply_id of the resul...
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Database Operation usage of HIbernate
Which method of HIbernate is more appropriate to use in the SQL statement select name,sex from db, for example: public T findByID (ID id, I dbName) throws Exception;
public List<T> findAll(I dbName) throws Exception;
public List<T> findBy...
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Realize the if judgment of where of mysql
how to realize the if judgment of mysql. There is now a table with two key fields SELECT * FROM house WHERE price= 8500 OR shoufu= 30 I think, when the $price passed in by php is empty, the sql search statement is SELECT * FROM house WHERE s...
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The realization scheme of the top of the article
problem description: a blog system is being developed that needs to achieve the top of an article, and then the foreground will display the article (or more than one) at the top. What I want is to add a new field to determine whether it is a top article...
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The problem of obtaining values from multiple tables with SQL statements in thinkphp
Table 1 fields are as follows
2
3
1event_description_description_id2id1cel_order_item_order_item_id3id
123idnull
id
ask the boss for advice
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What does the MySQL collation mean?
I have found many articles on utf8_unicode_ci, utf8_general_ci and utf8_bin collation on the Internet, and I generally know that ci is case ignore, etc., but I didn t mention what other collations mean .
what does the utf8mb4_polish_ci collation her...
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Mysql merge two query results are overwritten
uses union all to merge query results when doing a comprehensive statistical function, but the result set obtained by the query is found to be overwritten
sql:
SELECT
studyCenterName,
grade,
weiji,
done,
zong
FROM
(
...
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Case insensitivity of like query in MySQL5.7
for example, I like % R% answer, the query results include not only R, but also r, which is not what I want, I want to be case-sensitive. I guess it has something to do with the proofreading rules of the table. My table uses utf8mb4 encoding, and the pr...
