Summary of common SQL statements

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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）.........