1、简单查询:
SQL:
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SELECT
* FROM
[Clients] WHERE
Type=1 AND
Deleted=0 ORDER
BY
ID
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//Func形式
var
clients = ctx.Clients.Where(c => c.Type == 1 && c.Deleted == 0)
.OrderBy(c => c.ID)
.ToList();
//Linq形式
var
clients = from
c in
ctx.Clients
where
c.Type == 1 && c.Deleted==0
orderby
c.ID
select
c;
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2、查询部分字段:
SQL:
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SELECT
ID, Name
FROM
[Clients] WHERE
Status=1
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//Func形式
var
clients = ctx.Clients.Where(c => c.Status == 1)
.Select(c => new
{ c.ID, Name = c.ComputerName })
.ToList();
//Linq形式
var
clients = from
c in
ctx.Clients
where
c.Status == 1
select
new
{ c.ID, Name = c.ComputerName }; :
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3、查询单一记录:
SQL:
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SELECT
* FROM
[Clients] WHERE
ID=100
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//Func形式
var
client = ctx.Clients.FirstOrDefault(c => c.ID == 100);
//Linq形式
var
client = ( from
c in
ctx.Clients
where
c.ID = 100
select
c).FirstOrDefault();
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4、LEFT JOIN 连接查询
SQL:
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SELECT
c.ID ,
c.ComputerName ,
g. Name
GroupName
FROM
[Clients] c
LEFT
JOIN
[Groups] g ON
c.GroupID = g.ID
WHERE
c.Status = 1
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//Func形式
var
clients = ctx.Clients.Where(c => c.Status == 1)
.Select(c => new
{
c.ID,
c.ComputerName,
GroupName = ctx.Groups.FirstOrDefault(g => g.ID == c.GroupID).Name
})
.ToList();
//Linq形式
var
clients = from
c in
ctx.Clients
where
c.Status == 1
select
new
{
c.ID,
c.ComputerName,
GroupName = ( from
g in
ctx.Groups
where
g.ID == c.GroupID
select
g.Name).FirstOrDefault()
};
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5、INNER JOIN 连接查询:
SQL:
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SELECT
c.ID ,
c.ComputerName ,
g. Name
GroupName
FROM
[Clients] c
INNER
JOIN
[Groups] g ON
c.GroupID = g.ID
WHERE
c.Status = 1
ORDER
BY
g. Name
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//Func形式
var
clients = ctx.Clients.Where(c => c.Status == 1)
.Join(ctx.Group, c => c.GroupID, g => g.ID, (c,g) =>
{
c.ID,
c.ComputerName,
GroupName = g.Name
})
.OrderBy(item => item.GroupName)
.ToList();
//Linq形式1
var
clients = from
c in
ctx.Clients
from
g in
ctx.Groups
where
c.GroupID == g.ID
orderby
g.Name
select
new
{
c.ID,
c.ComputerName,
GroupName = g.Name
};
//Linq形式2
var
clients = from
c in
ctx.Clients
where
c.Status == 1
join
g in
ctx.Group
on
c.GroupID equals
g.ID into
result
from
r in
result
order by
r.Name
select
new
{
c.ID,
c.ComputerName,
GroupName = r.Name
};
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6、分页
SQL:
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-- 方案1
SELECT
TOP
10
*
FROM
[Clients]
WHERE
Status = 1
AND
ID NOT
IN
( SELECT
TOP
20
ID
FROM
[Clients]
WHERE
Status = 1
ORDER
BY
ComputerName )
ORDER
BY
ComputerName
--方案2
SELECT
*
FROM
( SELECT
* ,
ROW_NUMBER() OVER ( ORDER
BY
ComputerName ) AS
RowNo
FROM
[Clients]
WHERE
Status = 1
) t
WHERE
RowNo >= 20
AND
RowNo < 30
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//Func形式
var
clients = ctx.Clients.Where(c => c.Status=1)
.OrderBy(c => c.ComputerName)
.Skip(20)
.Take(10)
.ToList();
//Linq形式
var
clients = ( from
c in
ctx.Clients
orderby
c.ComputerName
select
c).Skip(20).Take(10);
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7、分组统计:
SQL:
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SELECT
Status ,
COUNT (*) AS
Cnt
FROM
[Clients]
GROUP
BY
Status
ORDER
BY
COUNT (*) DESC
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//Func形式
var
result = ctx.Clients.GroupBy(c => c.Status)
.Select(s => new
{
Status = s.Key,
Cnt = s.Count()
})
.OrderByDescending(r => r.Cnt);
//Linq形式
var
result = from
c in
ctx.Clients
group
c by
c.Status into
r
orderby
r.Count() descending
select
new
{
Status = r.Key,
Cnt = r.Count()
};
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