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首页第22讲 SQL语言高级06--子查询.PPT
第22讲 SQL语言高级06--子查询.PPT
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第22讲 SQL语言高级06--子查询.PPT第22讲 SQL语言高级06--子查询.PPT第22讲 SQL语言高级06--子查询.PPT第22讲 SQL语言高级06--子查询.PPT
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Subqueries

6-2
Objectives
After completing this lesson, you should be able to
do the following:
•
Describe the types of problem that subqueries can
solve
•
Define subqueries
•
List the types of subqueries
•
Write single-row and multiple-row subqueries

6-3
Using a Subquery
to Solve a Problem
Who has a salary greater than Abel’s?
Which employees have salaries greater
than Abel’s salary?
Main Query:
?
?
What is Abel’s salary?
?
?
Subquery

6-4
Subquery Syntax
•
The subquery (inner query) executes once before the main query.
•
The result of the subquery is used by the main query (outer
query).
SELECT select_list
FROM table
WHERE expr operator
(SELECT select_list
FROM table);
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