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Summary of common SQL statements
2020-11-06 21:19:00 【Irving the procedural ape】
One 、 Basics Sql sentence
1、 Create database :Create DataBase dbName;
2、 Delete database :Drop DataBase dbName;
3、 Create new table :Create Table tabName(col1 type1 [not null] [primary key] ,col2 type2 [not null ], ........);
There are two ways to create a new table from an existing table :A:Create Table tab_new like tab-old;
B:Create Table tab_new as Select col1,col2,....from tab_old definition only;
4、 Delete new table :Drop Table tabName;
5、 Add a column to the table :Alter Table tabName add column col type;
6、 Add and delete primary keys for tables : Add primary key :Alter Table tabName add primary key(col);
Delete primary key :Alter Table tabName drop primary key(col);
7、 Create and drop indexes for tables : Create index :Create [unique] index indexName on tabName(col ....)
Delete index :Drop index indexName;
8、 Create and delete views : Create view :Create view viewName as Select statement;
Delete view :Drop view viewName;
9、 Basic sql sentence : Inquire about :Select * from Table where Range ;Select * from Table where field1 like ‘%value1%'( Fuzzy query )
Insert :Insert into Table(field1,field2,...) values(value1,value2,.....);
Delete :Delete from Table where Range ;
· to update :Update Table set field1=value1 where Range ;
Sort :Select * from Table order by field1 Desc【 Descending 】| Asc【 Ascending 】;
total :Select count as TotalCount from Table ;
Sum up :Select sum(field1) as sumVaule from Table;
Average :Select avg(field1) as avgValue from Table;
Maximum :Select max(field1) as maxValue from Table;
Minimum :Select min(field1) as minVaule from Table;
10、Sql Several high-level query operation words in :
A: UNION Operator
UNION Operator by combining the other two result tables ( for example TABLE1 and TABLE2) And eliminate any duplicate rows in the table to derive a result table . When ALL along with UNION When used together ( namely UNION ALL), Don't eliminate duplicate lines . In both cases , Each row of the derived table does not come from TABLE1 Is from TABLE2.
B: EXCEPT Operator
EXCEPT Operator by including all in TABLE1 But not in TABLE2 The result table is derived by eliminating all duplicate rows . When ALL along with EXCEPT When used together (EXCEPT ALL), Don't eliminate duplicate lines .
C: INTERSECT Operator
INTERSECT The passage of the character only includes TABLE1 and TABLE2 The result table is derived by eliminating all duplicate rows . When ALL along with INTERSECT When used together (INTERSECT ALL), Don't eliminate duplicate lines .
notes : The result lines of several queries using operands must be consistent .
11、 Connect with the table :
(1) Internal connection (Inner Join):Inner Join TableName ON condition;
(2) Unequal value connection : Unequal value join means that less than can be used in the condition of connection (<)、 Greater than (>)、 It's not equal to (<>) Equal operator , It can also be used LIKE、BETWEEN AND Equal operator , You can even use functions . Example :Select field1,field2 from table1 Inner Jion table2 on table1.field1=table2.field1 where table1.field3<table2.field4
(3) Cross connect : Implicit :Select t1.field1,t2.field3 from table1 as t1,table2 as t2;
Explicit :Select t1.field1,t2.field3 from table1 as t1 cross Jion table2 as t2;
(4) External connection :A:Left outer Join ( The left outer join ( Left connection ): The result set includes both the matching rows of the join table , It also includes all the rows of the left join table );
B:Right outer Join ( Right connection ( The right connection ): The result set includes both the matching join rows of the join table , It also includes all rows of the right join table );
C:Full outer Join( Full outer join : Not only the matching rows of the symbolic join table , It also includes all the records in the two connection tables );
12、 Usage grouping Group by:
Example :Select Category , Abstract ,sum(field2) as sumValue from tableName Group by Category ;
notes : A watch , Once the grouping is complete , Only group related information can be obtained after query . Group related information :( Statistics ) count,sum,max,min,avg Criteria for grouping ); stay SQLServer In the middle group : Can't use text,ntext,image Fields of type are grouped by ; stay select Fields in statistical functions , It can't be put together with normal fields . In the use of Group by When you implement grouping , If there is where Filter conditions , Must be written in Group by Before .
13、Having Use :
For example, filter some groups , It needs to be used Having, Because aggregate functions can no longer Where Use in statement , So we have to use Having Instead of .
notes : Use Having When clause , It should be located in Group by after , also Having Statement cannot contain ungrouped column names .
Two 、 complex Sql sentence
1、 Copy table ( Copy only table structure ):Select * into b from a where 1<>1;Select top 0 * into b from a;
2、 Copy table ( Copy the data ):Insert into b(a,b,c) Select d,e,f from a;
3、 Subquery :
SELECT Statements can be nested in other statements , such as SELECT,INSERT,UPDATE as well as DELETE etc. , These are nested SELECT Statements are called subqueries , It can be said that subqueries can be used when a query depends on the results of another query . There are two types of subqueries , One is to return a single value subquery , It can be used in a place where a single value can be used , In this case, the subquery can be regarded as a function with a return value ; Another type of query is the return of a sub column , In this case, the subquery can be regarded as a temporary data table in memory .
(1) Single value subquery :
The syntax of single valued subquery and common SELECT There is no difference in the statement , The only limitation is that the return value of a subquery must have only one row of records , And there can only be one column . Such subqueries are also called scalar subqueries , Scalar subqueries can be used in SELECT In the list of statements 、 Expression 、WHERE The sentence is medium in many occasions . (2).........版权声明
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