Query for SQL tables

Select *  from  as T1 Select *  from dbo. Table_1  T1

As distinguished name \ All columns, partial columns

Query the first n part of the data:
Top N Column Name: Indicates the first n rows to view
Top N Percent Column name: Indicates the data for the first few percent of view

 select  *   From  dbo. Table_2--  Look at table 2nd, all data  select  top  3  *  from  dbo. Table_2--  No. 2nd table top three data  select  top  3  percent  *  from  dbo. Table_2--  2nd data before table 3 
  

Sort: Order By column name 1 asc|desc, column name 1 ASC|DESC ... desc descending asc Ascending row

Select *  from dbo. table_2orderbydescdesc-- check all data in table 2nd, sorted by Sid Descending, secondary to CID descending

Eliminate duplicate rows: Distinct

Select distinct  from dbo. Table_2-- Check table 2nd and delete duplicate rows in classid column

Where condition

Write in the Where: Filter the row, return a value of type bool, or join the result set if the column data in a row satisfies the condition

Comparison operators: =,>,>=,<,<=,!= or <>

Select  from where sid>2-- student number greater than 2 for all student names

Between ... Expressed in a contiguous range

Select  from where between 2  and 3 -- Student number 2 to 3 for all student names

In means within a discontinuous range

Select *  from where inch (3,1,6) -- Student number 1,3,6 all students

Logical operators: And,or,not

Select *  from where sid=3or sid=4-- student number 1,4 all students
SELECT * FROM dbo. table_2 where Sid not in (3,4,5)--student number not 3,4,5 all students

Fuzzy query: A value used to handle string types, including: like% _ []

Select *  fromTable_2whereSname like '%e%'--Check the information in the name of table 2nd with ESelect *  fromTable_2whereSname like 'q%'--Query the information in the name of table 2nd with the beginning of QSelect *  fromTable_2whereSphone like '1[5-9]%'--for information on mobile phone number 15~19 in table 2ndSelect *  fromTable_2whereSphone like '1[^5-9]%'--Check the phone number in table 2nd is not 15~19 information

% with _ written in [] means that the meaning of itself in [] indicates that a contiguous range can be written in [] at the beginning of the []-^, indicating that no internal characters are used

The LIKE keyword% represents 0 to more arbitrary characters _ an arbitrary character "^ non"

NULL judgment: null is used when computed with other values, NULL is considered to be the smallest when evaluated with IS NULL or is not NULL

Select *  from where  is NULL -- Query number 2nd number in the table is null information Select *  from where  is  not NULL -- Query the phone number in table 2nd is not null information

Query for SQL tables