Fuzzy query of SQL

When making a database query , There are complete query and fuzzy query .

General fuzzy query statements are as follows ：
 

SELECT Field FROM surface WHERE A field Like Conditions

It's about conditions ,SQL Four matching patterns are provided ：

1,% ： Express arbitrarily 0 Characters or more . Matches characters of any type and length , In some cases, it's Chinese , Please use two percent signs （%%） Express .

such as SELECT * FROM [user] WHERE u_name LIKE '% 3、 ... and %'

It will put u_name by “ Zhang San ”,“ Zhang maosan ”、“ Three legged cat ”,“ Tang Sanzang ” Wait, there are “ 3、 ... and ” I've got all my records .

in addition , If you need to find out u_name There is already “ 3、 ... and ” And then there is “ cat ” The record of , Please use and Conditions
SELECT * FROM [user] WHERE u_name LIKE '% 3、 ... and %' AND u_name LIKE '% cat %'

If you use SELECT * FROM [user] WHERE u_name LIKE '% 3、 ... and % cat %'
Although we can find out “ Three legged cat ”, But you can't find the right ones “ Zhang maosan ”.

2,_ ： Represents any single character . Match a single arbitrary character , It is often used to limit the character length of an expression ：

such as SELECT * FROM [user] WHERE u_name LIKE '_ 3、 ... and _'
Just find out “ Tang Sanzang ” such u_name It's three words and the middle word is “ 3、 ... and ” Of ;

Another example SELECT * FROM [user] WHERE u_name LIKE ' 3、 ... and __';
Just find out “ Three legged cat ” such name It's three words and the first word is “ 3、 ... and ” Of ;


3,[ ] ： Represents one of the characters listed in brackets （ Like regular expressions ）. Specify a character 、 String or range , Require the matched object to be any of them .

such as SELECT * FROM [user] WHERE u_name LIKE '[ Zhang liwang ] 3、 ... and '
Will find out “ Zhang San ”、“ Li San ”、“ The king of the three ”（ instead of “ Zhang Li, Wang San ”）;

Such as [ ] There's a series of characters in it （01234、abcde And so on. ） It can be abbreviated as “0-4”、“a-e”
SELECT * FROM [user] WHERE u_name LIKE ' The old [1-9]'
Will find out “ The old 1”、“ The old 2”、……、“ The old 9”;

4,[^ ] ： Represents a single character that is not listed in parentheses . Its value and [] identical , But it requires the matched object to be any character other than the specified character .

such as SELECT * FROM [user] WHERE u_name LIKE '[^ Zhang liwang ] 3、 ... and '
Will find out the last name “ Zhang ”、“ Li ”、“ king ” Of “ Zhao San ”、“ Sun San ” etc. ;

SELECT * FROM [user] WHERE u_name LIKE ' The old [^1-4]';
Will exclude “ The old 1” To “ The old 4”, seek “ The old 5”、“ The old 6”、……

5, When the query contains wildcards

Because of wildcards , Causes us to query for special characters “%”、“_”、“[” The statement cannot be implemented properly , And use special characters with “[ ]” You can query it normally . So let's write the following function ：
 

function sqlencode(str) str=replace(str,"[","[[]") ' This sentence must come first str=replace(str,"_","[_]") str=replace(str,"%","[%]") sqlencode=str end function

Before querying, the string to be queried can be processed by this function , And when you connect to a database on a web page and use such query statements, you should pay attention to ：

Such as Select * FROM user Where name LIKE ' The old [^1-4]'; above 《'》 The old [^1-4]《'》 It has to have single quotation marks , Don't forget , I often forget ！

 

access

Write in recent days Web The program uses Access Fuzzy query of , stay Acces I can't find any records in the code , Later, I got up. It turned out Acess and SqlServer Fuzzy query has special
Conditions : Lookup table A Of Name The field includes "B" Remember when
stay Access Code in :

1 Select * from a where name like '*b*'Sql Server Query analyzer code
Select * from a where name like '%b%' Then you will find Access Relevant records can be found in , But put '*' Bi Cheng '%' I can't find , as a result of Access The fuzzy query is '?','*'
and Sql server Dissimilarity
The above is just the code in the database , If you want to write it in the program, you can't use .'*' 了 , Still need to use '%'
Program :
strSql="select * from a where name like '%b%'" So if a friend likes to test the code in the database as much as I do , Then pay attention !!

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SQL Fuzzy query , Use like Compare keywords , add SQL The wildcards in , Please refer to the following ：
1、LIKE'Mc%' Will search with letters Mc All strings at the beginning （ Such as McBadden）.
2、LIKE'%inger' Will search with letters inger All strings at the end （ Such as Ringer、Stringer）.
3、LIKE'%en%' Will search to include letters anywhere en All strings of （ Such as Bennet、Green、McBadden）.
4、LIKE'_heryl' Will search with letters heryl All six letter names at the end （ Such as Cheryl、Sheryl）.
5、LIKE'[CK]ars[eo]n' The following string will be searched ：Carsen、Karsen、Carson and Karson（ Such as Carson）.
6、LIKE'[M-Z]inger' Search as string inger ending 、 From the M To Z All names beginning with any single letter of （ Such as Ringer）.
7、LIKE'M[^c]%' Will search with letters M start , And the second letter is not c All the names of （ Such as MacFeather）.
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Next The query string of face is what I wrote before , According to the variable zipcode_key In the zip code table zipcode Query the corresponding data in , This sentence is a judgment variable zipcode_key Query statement when it is non numeric , use % To match any length of string , Address from table 、 City 、 Save three columns to query all data items containing keywords , And by province 、 City 、 Address sorting . This is a simple example , As long as you understand the method, you can write more Complex query statements .

sql = "select * from zipcode where (address like'%" & zipcode_key & "%') or (city like'%" & zipcode_key & "%') or (province like'%" & zipcode_key & "%') order by province,city,address

Examples of using fuzzy queries in stored procedures ：

SELECT * FROM Questions where QTitle like ' % [ '+ @KeyWord +' ] % ' and IsFinish = @IsFinsih

Pairs of square brackets in a statement   Is the key to writing format .