标签：
1. Single-relation queries 2. Multi-relation queries 3. Subqueries 4. Grouping and Aggregation
（1）SELECT - FROM - WHERE statements
SELECT ... (desired attributes)
From ... （one or more tables）
WHERE ...（ condition about tuples of the tables）
EX: Using Beers(name, manf), what beers are made by Busch?
SELECT name, FROM Beers, WHERE manf = ‘Busch‘
（2）When there is one relation in the FROM clause, SELECT * clause stands for “all attributes of this relation.”
（3）If you want the result to have different attribute names, use “AS <new name>” to rename an attribute.
EX:Example based on Beers(name, manf):
SELECT name AS beername, manf FROM Beers WHERE manf = ‘Busch’
（4）SQL allows duplicates in relations as well as in query results.
To force the elimination of duplicates, insert the keyword distinct after select.
Find the names of all branches in the loan relations, and remove duplicates
select distinct branch_name from loan
The keyword all specifies that duplicates not be removed.
select all branch_name from loan
(5)Any expression that makes sense can appear as an element of a SELECT clause.
SELECT bar, beer, price * 6 AS priceInYuan FROM Sells;
（6）function 查询全体学生的姓名、出生年份和所有系，要求用小写字母表示所有系名。
SELECT Sname，2006-Sage AS ‘Year of Birth: ‘ ， LOWER(Sdept) FROM Student；
(7)What we can use in select clause :
expressions
constants
functions
Attribute alias
（8）What you can use in WHERE:
attribute names of the relation(s) used in the FROM.
comparison operators: =, <>, <, >, <=, >=, between, in
apply arithmetic operations: stockprice*2
operations on strings (e.g., “||” for concatenation).
Lexicographic order on strings.
Pattern matching: s LIKE p
Special stuff for comparing dates and times.
（9）Range comparison: between
查询年龄在20~23岁（包括20岁和23岁）之间的学生的姓名、系别和年龄。
SELECT Sname，Sdept，Sage FROM Student WHERE Sage BETWEEN 20 AND 23；
（10）Set operator: in
使用谓词： IN <值表>, NOT IN <值表>
<值表>： 用逗号分隔的一组取值
[例]查询信息系（IS）、数学系（MA）和计算机科学系（CS）学生的姓名和性别。
SELECT Sname，Ssex FROM Student WHERE Sdept IN ( ‘IS‘，‘MA‘，‘CS‘ );
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原文地址：http://www.cnblogs.com/zpfbuaa/p/5358035.html
