SQL Server database design -- select statement 2

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In the last article, I introduced SQL SERVER Of SELECT Simple use of statements 《​ ​SQL Server Database design --SELECT sentence ​​》, This article continues to introduce other commonly used query methods .

First of all , Used in query results LIKE And wildcards

The figure above shows 4 How to use wildcards in . The following is a practical example
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       ' When using Chinese in query , Sometimes data cannot be queried , There are corresponding records in the actual records , It's usually 
       
       
' Due to coding problems , Chinese characters can be prefixed with N, Such as : N‘ Li %’
       
       
' Use wildcards %, Inquire about StudentName The first word in is Li , Follow any number or one word 
       
       
SELECT StudentName, phone, Address, IDENTITYcard
       
       
FROM Student WHERE StudentName LIKE ‘ Li %’
       
       
' Use wildcards _, Inquire about StudentName The first word in is Li , Any word after 
       
       
SELECT StudentName, phone, Address, IDENTITYcard
       
       
FROM Student WHERE StudentName LIKE ‘ Li _’
       
       
' Use wildcards [], Inquire about StudentName The first word in is any character of Zhang Wang Li , Any number of words after 
       
       
SELECT StudentName, phone, Address, IDENTITYcard
       
       
FROM Student WHERE StudentName LIKE ‘[ Zhang Wang Li ]%’
       
       
' Use wildcards [^], Inquire about StudentName The first word in is not in any character of Zhang Wang Li 
       
       
SELECT StudentName, phone, Address, IDENTITYcard
       
       
FROM Student WHERE StudentName LIKE ‘[^ Zhang Li ]%’
      
      
      
      

       
       
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second , Use operators in queries

The meaning of commonly used operators is introduced in the figure above . The following is a practical example
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（1） The operator BETWEEN ... AND Select a data range between two values . Value can be numeric 、 Text or date .

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       SELECT * FROM Result WHERE Result BETWEEN 50 AND 90
       
       
SELECT * FROM Result WHERE Result NOT BETWEEN 50 AND 90
      
      
      
      

       
       
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（2） Use of comparison , It doesn't mean there are two ：<>, !=
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       SELECT * FROM Result WHERE (Result > 50) AND (Result 
       
       < 
       
       80)
      
      
      
      

       
       
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（3） The operator IN Allow in WHERE Multiple values specified in clause . You can also use NOT IN
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       SELECT StudentName,phone, Address, IDENTITYcard
       
       
FROM Student WHERE StudentName IN (N' Li lei ',N' Li Mochou ')
      
      
      
      

       
       
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（4） Sort query results （ASC: Ascending ,DESC: Descending ）
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       SELECT * FROM Result ORDER BY Result ASC -- Default ascending order , No addition ASC
       
       
SELECT * FROM Result WHERE Result > 50 ORDER BY Result DESC
       
       
SELECT * FROM Student ORDER BY [ID] ASC, [IDENTITYcard] DESC -- Multi column sorting 
      
      
      
      

       
       
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（5） Use IS NULL Query null value , Out of commission ” =NULL ”

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       SELECT * FROM Student WHERE phone IS NULL -- Inquire about phone Empty record 
       
       
SELECT * FROM Student WHERE phone IS NOT NULL -- Inquire about phone Not empty record 
      
      
      
      

       
       
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Don't go away , The next article will continue to introduce more advanced query functions .

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Author's brief introduction

Sword control Lao Luo

have 10 In the field of industrial automation SCADA,DCS,PLC And other project implementation experience , Familiar with petrochemical industry , Oilfield digitization industry , Familiar with multiple brands PLC,HMI,SCADA, Database etc. .

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