how to write distinct query in sql

In fact, this is also a problem at work. To tell the truth, I am not willing to do it myself. I also want to write statements for queries, but I have not thoroughly studied this kind of information,Write SQL statements in JavaProgramAt the same time, I chose to be lazy. First, if it is golden, of course there is no need to say that the Direct

Ah, content Ah, subtitle Ah, xxoo on those things, and then, even the table is not built, directly with the entity class can generate tables, additions and deletions to check. In the show, using an ORM query, even SQL injection is automatically to you, it looks really good. Yes, it's good. But here is a very serious problem, the article input is of course no problem, but in the article List page, the prob

Except those who do not know what paging is, most people think of a word called LIMIT. Unfortunately, DB2 does not support this keyword, so how do I write the DB2 paging query? As long as you have learned OLAP functions, paging query is very simple. Even if you do not use OLAP functions, follow the following SQL Except

]);$data = $query->all();$data = $query->one(); In fact, there are many database query methods in the yii framework, such: $data = JdCrmSmsUserModel::find()->where([ 'vender_id' => [ $venderId ] ])->all(); Or use findBySql (), findOne (), findAll (), and so on to replace find () for

; count (); // obtain the total number of users.$ Arr = $ m-> where ("username = 'gege'")-> count (); // place the string $ M = M ('user ');$ Data ['username'] = 'gege'; // place an array$ C = $ m-> where ($ data)-> count (); // The array operation is more standard. III. SQL direct query. A. The primary number of queries processes the data read. The result set is returned successfully. if the

relationship. Ii. statistical query: Count // obtain the numberMax // obtain the maximum numberMin // obtain the minimum numberAvg // obtain the averageSum // get the sum The Code is as follows: $ M = M ('user ');$ Arr = $ m-> count (); // obtain the total number of users.$ Arr = $ m-> where ("username = 'gege'")-> count (); // place the string $ M = M ('user ');$ Data ['username'] = 'gege'; // place an array$ C = $ m-> where ($ data)-> count (); //

[Zhuantang learning notes] basic SQL query statements (single-Table query and multi-Table query)SQLQueryBasic1. Single Table query It is also called projection. Basic query statement Structure Select column from table * Not all ot

SQL two simple paging query methods, SQL paging Query Method In the past, we may have used the skip and take method of linq for paging queries, but few of them write SQL paging queries by themselves, because most of the time, we

' --true display, false --where birthday> ' 1990-01-01 ' SELECT sex from info WHERE SEX was not NULL SELECT SNAME from info WHERE SNAME like '% Month ' ------back up INFO table to Info--bak --1 Info_bak -- 2 Insert query Data Select *into Intfo_bak from INFO-two functions to create a new table Insert query data --note constraint does not back up identity property backup (Identity) SELECT * into Inf

; count (); // obtain the total number of users.$ Arr = $ m-> where ("username = 'gege'")-> count (); // place the string $ M = M ('user ');$ Data ['username'] = 'gege'; // place an array$ C = $ m-> where ($ data)-> count (); // The array operation is more standard. III. SQL direct query. A. The primary number of queries processes the data read. The result set is returned successfully. if the

After sqlserver2005, MSSQL began to use the recursive query method. Compare the methods for writing stored procedures or functions at the beginning. This method is simpler and more flexible. Oracle also has its own tree structure recursive query method, connect Next I will write a piece of SQL code by myself, and b

. How to make the database use indexes as we mean involves the concept of scan parameters (SARG. In the query and analysis stage, the database engine uses the query optimizer to analyze each stage of the query (for example, different query stages exist for an SQL statement w

My Date The first date format we get is this: 2009-2-12 or 2009-3-3 or 2009-10-12, we can do this by combining SQL statements: (three examples) The code is as follows Copy Code @1select * from user where birthday> ' 2009-2-3 ' and birthday This allows us to find all user information that includes 2009-2-3 and is greater than 2009-2-3. @2 If that's how we mix it. The code is as follows Copy Code

$c = $m->where ($data)->count (); Array Operations Compare specifications three, SQL direct query , very flexible can do more operations. A, query main number processing read data, successfully returned the result set of data, failed to return Boolean false Copy Code code as follows: $m =m (); $result = $m->

; where ($ data)-> count (); // The array operation is more standard. You can use SQL to directly query and perform more operations flexibly. A. The primary number of queries processes the data read. The result set is returned successfully. if the query fails, the return value is boolean false. $ M = M (); $ Result = $ m->

Analyzer is considered to be two different SQL statements, must be parsed two times. Generate 2 execution plans. So as a programmer, you should ensure that the same query statements everywhere are consistent, one more space is not! 3. Do not write SQL statements too complex I often see a

considered to be two different SQL statements, must be parsed two times. Generate 2 execution plans. So as a programmer, you should ensure that the same query statements everywhere are consistent, one more space is not!3. Do not write SQL statements too complexI often see a SQL