SELECT Statements: SyntaxNOTE: SQL commands are not case sensitive. The above SELECT statement can also be written as"select first_name from students_details;" You can also retrieve data from more than one column. For example, to select first name and last name of all the students. ...
UNION运算符可以将两个或两个以上上SELECT语句的查询结果集合合并成一个结果集合显示,即执行联合查询。UNION的语法格式为: select_statement UNION [ALL] selectstatement [UNION [ALL] selectstatement][…n] 其中selectstatement为待联合的SELECT查询语句。 ALL选项表示将所有行合并到结果集合中。不指定该项时,被联合...
数据查询语言(DQL,Data Query Language):用于从表中获得数据,关键字是SELECT 实际应用中,我们通常是编写SQL语句,提交给数据库或大数据系统来执行,然后获取执行结果;有几个容易搞迷糊的概念如下: Statement:语句,通常指整个SQL文本 Clause:子句,通常指SQL文本中的一部分,如From子句、Where子句、Group By子句 Query:查询...
select_statement union [all] select_statement all代表最终的结果集中将包含所有的行,而不能删除重复行。 示例: SELECT Name FROM Person_1 UNION SELECT Name FROM Person_2 生成的结果为: 注意到重复记录,孙权与周瑜仅仅显示了一个。下面来将UNION替换成UNION ALL看看是什么结果: SELECT Name FROM Person_1 U...
Select statement union | union all Select statement; 1.2.intersect交集操作 相交运算 用相交运算返回多个查询中所有的公共行。 无重复行。 原则 ?在查询中被 SELECT 语句选择的列数和数据类型必须与在查询中所使用的所有的 SELTCT 语句中的一样,但列的名字不必一样。
statement selectsallrowsifthereisnoWHEREclause.IntheWHEREexpression, you canuseanyofthe functionsandoperators that MySQL supports,exceptforaggregate (summary) functions. See http://dev.mysql.com/doc/refman/8.0/en/expressions.html,andhttp://dev.mysql.com/doc/refman/8.0/en/functions.html.SELECTcan ...
The following query uses the SELECT statement to get all the last names from the lastname column in the employees table: SELECT lastname FROM employees;Code language: SQL (Structured Query Language) (sql) To specify multiple columns, you use a comma (,) like this: SELECT lastName, firstNam...
The SELECT statement is a common SQL statement. You’ll use it all the time. It can be as simple as selecting a few columns from a table, or it can include joins, functions, and grouping. You can also use subqueries and other more advanced features with it....
SELECT UnitPrice, OrderQty, UnitPrice * OrderQty AS Total FROM Purchasing.PurchaseOrderDetail The bit ” UnitPrice * OrderQty” says to multiply UnitPrice by Quantity. SQL Distinct So far we have used the select statement to retrieve all the records in a table regardless if some values repea...
Select ALL columns If you want to return all columns, without specifying every column name, you can use theSELECT *syntax: Example Return all the columns from the Customers table: SELECT*FROMCustomers; Try it Yourself » Video: SQL SELECT Statement ...