assign value to variable in sql select statement

Scenario: Update A field value with Update, which is made up of another field and a string in the same table SQL statement: The code is as follows Copy Code Update ' tablename ' Set Field1=concat (' tablename '. Field2, "str");

", we need to add a WHERE clause to the SELECT statement:WHERE City=‘Beijing‘"Persons" table LastName FirstName Address City Year Adams John Oxford Street London 1970 Bush George Fifth Avenue New York 1975 Carter Thomas Changan Street Beijing 1980 Gates Bill Xuanwumen 10 Beijing

Sometimes we need to calculate the average value every half hour, so we need to refer to the following SQL statement table structure: Create table 'instance' ('id' int (11) unsigned not null AUTO_INCREMENT, 'timestamp' int (10) unsigned default null, 'CPU' decimal (8, 3) default null, primary key ('id') ENGINE = InnoDB; Calculate the average

SELECT statement The SELECT statement is already useful in the previous tutorial. It is described in detail in the tutorial in this section. The SELECT statement is the core of SQL, and

where is used for the first query, and the having statement is used for two queries.Order clauseORDER by Col_name [asc| DESC]Col_name indicates which field to sort[asc| The DESC]:ASC represents a sort in ascending order, and Desc is sorted in descending order. The default is to sort in ascending order.Limit clauseLIMIT [Offset,] countLimit at the end of the statement, play the role of restricting entriesOf

Label:1. First, select top usage:Reference question the difference between select top N * FROM and select * FROM Select * from table--Fetch all data, return unordered collection Select top n * from table -Returns an unordered collection based on the first n of the data

The SELECT statement is used to select data from the table. The result is stored in a result table (called a result set). SQL SELECT syntaxSelect Column name from table name and: SELECT * FROM table name NOTE:

Label:Like statements in SQL have irreplaceable important role, the following will introduce you to the SQL statement in the details of the use of a, I hope you can help.The syntax format for the LIKE statement is: SELECT * from table name where field name like corresponding

Lee 490 85 953 Wang 588 75 90The converted table structure:ID Name Account Score1 in three languages 802 Zhang Three Mathematics 903 three English 704 John Doe Language 905 John Doe Mathematics 806 John Doe English 997 Harry Language 858 Harry Mathematics 969 Harry English 88Table of horizontal Tables SQL example:SELECT name, ' language ' as subject, language as score from test_h2z UNION allSELECT name, ' Math ' as subject, math as score from test_h2

-------------100302070901105040801060Rows selectedSQL Statement and sql*plus command Structural Query LanguageSql?A language?ANSI Standard?Keywords cannot be abbreviated?Use statements to control the definition information of tables in a database and the data in a tableSql*plus?An environment?One of the features of Oracle?Keywords can be abbreviated Desc EMPLOYEES,DESC is the keyword of

SQL Single Table/multiple table query removal duplicate record single table distinct multiple table group byGroup byMust be placed inOrder byand limit before the error will be************************************************************************************1, duplicate records in the lookup table are judged by a single field (Peopleid) .Select * frompeoplewherePeopleidinch(SelectPeopleid fromPeopleGrou

Label:Select date_format (server_time, '%h:%i '), (sum (flow_value)-max (flow_value)-min (Flow_value))/7 from t Able_name where server_time >= ' Date9 00:00:00 ' and Server_time SQL (MYSQL) statement for the average of the same time for the last 9 days (minus the maximum, minimum value)

Label:SQL SELECT DISTINCT StatementIn the table, duplicate values may be included. That's not a problem, but sometimes you might want to just list different values (distinct). Keyword DISTINCT is used to return only different values.Grammar:SELECT DISTINCT (directory field) column name from table name (AA)Using DISTINCT KeywordsIf you want to pick all the values from the company column, we need to use the SELECT