oracle学习笔记2-Restricting and sorting data
2005-12-17 21:23
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Objectives:
After completing this lesson,you should be a able to do the following:
Limit the rows retrieved by a query
Sort the rows retrieved by a query
Limiting the rows selected:
Restrict the rows returned by using the WHERE clasue.
e:select * from table where ;
The WHERE clasue follows the FROM clause.
Character strings and dates:
Character strings and date values are enclosed in single quotation marks.
Character values are case sensitive,and date values are format sensitive.
The default date format is DD-MON-RR.
Comparison conditions:
equal to,greater than,not equal to,....
Other comparison conditions:
Between ..and....
e:select * from sales where qty
between 10 and 50;
In(set)
e:select * from sales
where name_id in('zhou','fa');
like,is null,
Using the LIKE condition:
Use the LIKE condition to perform wildcard searches of valid search string values.
Search conditions can contain either literal characters or numbers:
@% denotes zero or many characters.
e:select * from sales
where name_id like 'B%';
@_denotes one character.
Logical conditions:
and,or,not;
Rules of precedence:
arithmetic perators,concatenation conditions,comparison conditions.
not ,and, or
ps:if change rules of precedence,can use ().
Order by clause:
Sort rows with order by clause
@ASC:asceding order,default
e:select * from sales
order by name_id;
@DESC:descending order
e:select * from sales
order by name_id desc;ps:(must write parm)
The order by clause comes last in the SELECT statement.
Sorting by cloumn alias
Sorting by multiple columns:
The order of ORDER BY list if the order of sort.
e:select * from sales
order by name_id ,(salary desc);
After completing this lesson,you should be a able to do the following:
Limit the rows retrieved by a query
Sort the rows retrieved by a query
Limiting the rows selected:
Restrict the rows returned by using the WHERE clasue.
e:select * from table where ;
The WHERE clasue follows the FROM clause.
Character strings and dates:
Character strings and date values are enclosed in single quotation marks.
Character values are case sensitive,and date values are format sensitive.
The default date format is DD-MON-RR.
Comparison conditions:
equal to,greater than,not equal to,....
Other comparison conditions:
Between ..and....
e:select * from sales where qty
between 10 and 50;
In(set)
e:select * from sales
where name_id in('zhou','fa');
like,is null,
Using the LIKE condition:
Use the LIKE condition to perform wildcard searches of valid search string values.
Search conditions can contain either literal characters or numbers:
@% denotes zero or many characters.
e:select * from sales
where name_id like 'B%';
@_denotes one character.
Logical conditions:
and,or,not;
Rules of precedence:
arithmetic perators,concatenation conditions,comparison conditions.
not ,and, or
ps:if change rules of precedence,can use ().
Order by clause:
Sort rows with order by clause
@ASC:asceding order,default
e:select * from sales
order by name_id;
@DESC:descending order
e:select * from sales
order by name_id desc;ps:(must write parm)
The order by clause comes last in the SELECT statement.
Sorting by cloumn alias
Sorting by multiple columns:
The order of ORDER BY list if the order of sort.
e:select * from sales
order by name_id ,(salary desc);
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