Mssqlserver SQL basics

1. Description: create a database
Create DATABASE database-name
2. Description: Delete a database.
Drop database dbname
3. Description: create a new table
Create table tabname (col1 type1 [not null] [primary key], col2 type2 [not null],...)
Create a new table based on an existing table:
A: create table tab_new like tab_old (use the old table to create A new table)
B: create table tab_new as select col1, col2... From tab_old definition only
4. Description: delete a new table.
Drop table tabname
5. Description: add a column.
Alter table tabname add column col type
Note: columns cannot be deleted after they are added. After columns are added to DB2, the data type cannot be changed. The only change is to increase the length of the varchar type.
6. Description: add a primary key: Alter table tabname add primary key (col)
Delete a primary key: Alter table tabname drop primary key (col)
7. Description: create an index: create [unique] index idxname on tabname (col ....)
Delete index: drop index idxname
Note: The index cannot be changed. To change the index, you must delete it and recreate it.
8. Description: create view viewname as select statement
Delete view: drop view viewname
9. Description: several simple basic SQL statements
Select: select * from table1 where range
Insert: insert into table1 (field1, field2) values (value1, value2)
Delete: delete from table1 where range
Update: update table1 set field1 = value1 where range
Search: select * from table1 where field1 like '% value1 %'
Sort: select * from table1 order by field1, field2 [desc]
Total: select count as totalcount from table1
Sum: select sum (field1) as sumvalue from table1
Average: select avg (field1) as avgvalue from table1
Max: select max (field1) as maxvalue from table1
Min: select min (field1) as minvalue from table1
10. Description: several advanced query operators
A: UNION operator
The UNION operator combines two other result tables (such as TABLE1 and TABLE2) and removes any duplicate rows from the table to generate a result table. When ALL is used together with UNION (that is, union all), duplicate rows are not eliminated. In either case, each row of the derived table is from either TABLE1 or Table2.
B: random T operator
The distinct T operator derives a result table by including all rows in Table 1 but not in table 2 and eliminating all repeated rows. When ALL is used with distinct T (distinct t ALL), duplicate rows are not eliminated.
C: INTERSECT operator
The INTERSECT operator derives a result table by only including the rows in TABLE1 and TABLE2 and eliminating all repeated rows. When ALL is used with INTERSECT (intersect all), duplicate rows are not eliminated.
Note: the query results of several computation words must be consistent.
11. Note: Use external connections
A. left outer join:
Left outer join (left join): the result set contains the matched rows in the connected table, and all rows in the left connected table.
SQL: select a. a, a. B, a. c, B. c, B. d, B. f from a left out join B ON a. a = B. c
B: right outer join:
Right outer join (right join): the result set includes both matched join rows in the connection table and all rows in the right join table.
C: full outer join:
Full outer join: includes not only matching rows in the symbolic join table, but also all records in the two join tables.