how to use order by

Cases The code is as follows Copy Code SELECT cat. ' Name ', class. ' Title 'From ' Cat ', ' class 'WHERE cat. ' id ' = class. ' Cat 'and cat. ' ID ' =2LIMIT 0, 30DELETE cat, class from Cat, Class WHERE cat. ' ID '

First, table design1. Library name, table name, field name use lowercase letters, "_" split.2. The Library name, table name, field name is not more than 12 characters.3. The Library name, table name, field name are known, try to use nouns rather

1.Sub-querySubqueries are also called nested clause queries.1.1.GrammarSyntax for running usage rules:L subqueries ( inner query, nested clauses ) are executed one time before the main query. (Sub-query executes first)the results of the subquery are

In the past, I always remember how to use GROUP BY, how to use order by, when to use Group by, when to use order by, when the two are used together, how to use, who first who, now, we say together Select from where groupby the things that have order

ObjectiveIn the previous section we briefly described the 4 types of table expressions, which we talked about using the view restrictions, short content, in-depth understanding, always to review the basics.Avoid using order by in viewsIn the

We have previously introduced the INSERT and REPLACE statements in MySQL database UPDATE statements. Today we will introduce the UPDATE, DELETE, and TRUNCATETABLE statements, and introduces the practical application functions of these statements.

How does MySQL simplify external Union? In many cases, the expression of a table in the FROM clause can be simplified. During the analysis phase, queries with right Outer Join Operations are converted to equivalent queries that only contain left

1. insert: (1) Insert multiple records simultaneously Insert into tab (col1, col2, col3) values (a1, a2, a3), (b1, b2, b3), (c1, c2, c3); compared to multiple insert records, this method reduces the number of SQL Analysis and Optimization times,

There are two ways to delete data in MySQL: one is the delete statement and the other is the truncate TABLE statement. You can use the WHERE clause to select the record to be deleted. However, using truncate table will delete all records in the

MySQL database insert and update statementsThe SQL statements used to operate databases are generally divided into two types: Query statements, SELECT statements, and update statements, which are also called data operation statements. The

Randomly recommended 10 users can use ORDER by rand (), but a large amount of data will affect efficiency $sql='select uid from member order by rand() limit 10'; Or a random uid, and then look from the UID, eg: for($i=0;$i The problem is that the

How does MySQL simplify external Union?In many cases, the expression of a table in the FROM clause can be simplified.During the analysis phase, queries with right outer join operations are converted to equivalent queries that only contain left join

Temporary Summary of Oracle databases-1 I haven't published a blog for a long time. I have learned mysql before learning oracle. I thought it would be much easier to learn oracle. However, I was wrong, oracle is more difficult than mysql, mainly in

The previous articles have provided the basic idea of diagnosing all aspects of the database from the whole ... Maybe it's very useful to you, maybe you feel too far away from yourself. So today we are going to make an introduction from some of the

In the past, I always remember how to use GROUP BY, how to use order by, when to use Group by, when to use order by, when the two are used together, how to use, who first who, now, let's go together. Select from where group By having an order by,

1. Aggregation functions (Aggregate function)MySQL (5.7) the list of aggregate functions given in the official documentation (image) is as follows:Click https://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html for details.Unless otherwise

SQL language is a very simple language, write SQL as long as you understand its execution logic can write the correct SQL statement!The most obvious difference between SQL statements and other programming languages is the order in which code is

Multiple table Updatesin MySQL 3.23, you can use LIMIT # to make sure that only a given number of record rows is changed. if an ORDER BY clause is used (supported from MySQL 4.0.0), the record row is updated in the specified order. This is actually

Many programmers view SQL as a scourge. SQL is one of the few declarative languages that run in a way that is completely different from the command-line language we know, the object-oriented programming language, or even the functional language

MySQL Injection module#coding:gb2312ImportUrllibImportstringImportBinasciiImportReclassmysqlinject ():def __init__(Self,url): Self.db='database ()'Self.url=url#URLs to be testedSelf.dblen=0#the length of the databaseSelf.counts=0#Number of