1. join
tips:
(1). inner join 同 join
selectalias_name1.column_name, alias_name2.column_name
from table_name1 as
alias_name1
inner
join table_name2 as
alias_name2
on alias_name1.column3 =
alias_name2.column4
order
by alias_name1.column_name1
(2). left join, 即使右表沒有匹配,也返回左表所有行
selectalias_name1.column_name, alias_name2.column_name
from table_name1 as
alias_name1
left
join table_name2 as
alias_name2
on alias_name1.column_name3 =
alias_name2.column_name4
order
by alias_name1.column_name1
(3). right join, 即使左表沒有匹配,也返回右表所有行
selectalias_name1.column_name, alias_name2.column_name
from table_name1 as
alias_name1
right
join table_name2 as
alias_name2
on alias_name1.column_name3 =
alias_name2.column_name4
order
by alias_name1.column_name1
(4). full join, 返回所有行
selectalias_name1.column_name, alias_name2.column_name
from table_name1 as
alias_name1
full
join table_name2 as
alias_name2
on alias_name1.column_name3 =
alias_name2.column_name4
order
by alias_name1.column_name1
2. union 合併多個select 語句的結果
tips:
select 語句必須有相同數量的列,且有相似的資料型別,列的順序也必須相同
union 預設返回不同的值
union all 允許返回重複的值
結果中的列名為第乙個select 語句中的列名
select column_name(s) fromtable_name1
union
select column_name(2) from table_name2
3. select into 從乙個表選資料插入另乙個表, 常用於備份復件或存檔記錄
select*into
new_table_name
from old_table_name
tips:
(1). 從externaldatabase 選
select*into
new_table_name
from externaldatabase_name.dbo.table_name
(2). 如果表2已經存在,則用 insert into
insertinto
table2_name(column1, column2,…)
select table1_column1,table1_column2,… from table1_name
4. constraint 約束
(1). not null
(2). unique 約束唯一,每個錶可有多個unique
可以不設定unique 名,系統有預設值,但是建議設定,方便使用; 可以同時設定多列
altertable table_name add
unique
(column_name)
alter
table table_name add
constraint uq_name unique
(column_name1,column_name2)
alter
table table_name drop
constraint uq_name
(3). primary key 約束唯一,每個表只有乙個primary key
altertable table_name add
constraint pk_name primary
key(column_name1,column_name2)
alter
table table_name drop
constraint pk_name
(4). foreign key
altertable table_name1 add
constraint fk_name foreign
key(column_name1) references
table_name2(column_name2)
alter
table table_name drop
constraint fk_name
(5). check 約束列中值的取值範圍
altertable table_name add
constraint chk_name check (column_name1 >
3and column_name2 like
'%abc%')
alter
table table_name drop
constraint chk_name
(6). default 設定預設值
altertable table_name add
constraint df_name default
'dafult_value
'for
column_name
alter
table table_name drop
constraint df_name
查詢表是否有default 約束
select*from sys.default_constraints where sys.default_constraints.parent_object_id=
object_id('
table_name
')
檢視表中的約束
exec sp_helpconstraint 'table_name
'
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