SQL SERVER 基礎語句學習 三

1. join

tips:

(1). inner join 同 join

select

alias_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

select

alias_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

select

alias_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

select

alias_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) from

table_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

insert

into
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

alter

table 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

alter

table table_name add
constraint pk_name primary
key(column_name1，column_name2)
alter
table table_name drop
constraint pk_name

(4). foreign key

alter

table 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

alter

table 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

alter

table 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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