如何使用正则表达式验证 SQL 查询？

通常，一行数据将由电子邮件地址、电话号码、字母/字母数字/数字值等组成，通常，前端验证用于验证电子邮件地址/电话号码等，在本文中，我们将了解如何在编写 SQL 查询时使用正则表达式对其进行验证。因为在后端传递相关数据总是好的。每当数据中出现错误时，正则表达式会快速验证并通知用户是成功还是失败。

第一步：创建数据库

询问：

SELECT * FROM sys.databases WHERE name = 'GEEKSFORGEEKS'
    BEGIN
    CREATE DATABASE [GEEKSFORGEEKS]
    END

第 2 步：在“GEEKSFORGEEKS”数据库下创建“GeekAuthors”表

询问：

use GEEKSFORGEEKS
CREATE TABLE GeekAuthors (
    ID INT IDENTITY NOT NULL PRIMARY KEY,
    AuthorName VARCHAR(255) NOT NULL,
    AuthorEmail VARCHAR(255) NOT NULL,
    Age INT,
    Skillsets VARCHAR(255),
    NumberOfPosts INT
);
GO

由于 AuthorEmail 是一个 varchar 列，因此在“GeekAuthors”表中输入了错误无效的电子邮件地址。我们的任务是找出获得无效电子邮件地址的行。

第 3 步：为了实现这一点，让我们将样本数据放在每一行中

INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Rachel','rachel@gmail.com',25,'Java,Python,.Net',5);
INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Phoebe','phoebegmailcom',22,'Android,Python,.Net',15);
INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Monica','monica@gmailcom',23,'IOS,GO,R',10);
INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Joey','joey@.com',24,'Java,Python,GO',5);
INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Chandler','chandler@gmail',23,'IOS,GO,R',10);
INSERT INTO GeekAuthors (AuthorName,AuthorEmail,Age,Skillsets,NumberOfPosts) 
VALUES ('Ross','ross@gmail.com',24,'Java,Python,GO',5);

第 4 步：现在我们验证电子邮件地址。

我们需要验证输入的电子邮件地址是否正确。为此，我们可以轻松实现

询问：

-- Get all email address
SELECT AuthorEmail FROM GeekAuthors
-- Get ValidEmail Address
SELECT AuthorEmail AS ValidEmail
FROM GeekAuthors
WHERE AuthorEmail LIKE '%_@__%.__%'
        AND PATINDEX('%[^a-z,0-9,@,.,_,\-]%', AuthorEmail) = 0
GO
-- use NOT condition in the WHERE clause and select all the invalid emails as well.
SELECT AuthorEmail AS NotValidEmail
FROM GeekAuthors
WHERE NOT AuthorEmail LIKE '%_@__%.__%'
        AND PATINDEX('%[^a-z,0-9,@,.,_,\-]%', AuthorEmail) = 0
GO

输出：

第 5 步：用于使用正则表达式从给定值中定位数值。可以通过两种方式找到

我们的输入表达式可能由字母数字值组成。为了找出数值在数据中的位置，我们可以使用下面的格式。

询问：

--pattern to check is: Not of  A-Z (both A-Z and a-z(search pattern))
-- in the input string and 
--finding the position of the non-matching pattern
-- As we are checking numeric values, it checks for numeric value position 
--and it is displaying position of the character
Way 1 :
SELECT 'GeekPremierLeague2022' as ContestName,
PATINDEX('%[^A-Za-z]%', 'GeekPremierLeague2022') as
NumericCharacterPosition;
Way 2 :
SELECT 'GeekPremierLeague2022' as ContestName, 
PATINDEX('%[0-9]%', 'GeekPremierLeague2022') as
NumericCharacterPosition;

输出：

如果数字不可用，我们将得到 0 作为答案

输出：

第 6 步：在少数情况下，我们可能只需要从输入字符串中提取字母 (az)。

可以通过组合 2 个函数，即 PATINDEX 和 STUFF 来实现。

必须在 PATINDEX 上应用正则表达式。使用上面的查询，我们将获得数字位置
通过使用 STUFF函数，我们可以替换所有数值。

询问：

-- At the 18th position, one character is replaced. 
We need to remove numeric value. 
-- Hence STUFF function is used
1st Param -- Input string
 2nd Param -- Start location . As numeric is present
  at 18th location, here it is given
 3rd Param -- Number of characters to be replaced 
 4th Param - Replacing value
SELECT STUFF('GeekPremierLeague2022', 18, 1, '' ); 
-- One character is replaced at the index 18
-- If we want to remove all the numeric above
SELECT STUFF('GeekPremierLeague2022', 18, 4, '' ); 
-- Four characters are replaced starting from  the index 18

输出：

因此，通过同时应用 PATINDEX 和 STUFF，我们可以删除给定字符串中的数值：

询问：

-- Below code will produce only alpha text only
-- Scenario: A column is created in a table to accept
   only alphabets. As there is no direct way available, 
-- we can use this approach and extract the alphabets alone
DECLARE @inputData NVARCHAR(MAX) = 'GEEKS PREMIER LEAGUE 2022'       
--input string
DECLARE @intPosition INT    
 --get the position of the integer from the input string   
SET @intPosition = PATINDEX('%[^A-Za-z]%', @inputData) 
-- We can use PATINDEX('%[0-9]%') also
print @intPosition
--run loop until no integer is found in the input string
WHILE @intPosition > 0                                     
  BEGIN  
     --remove the integer from that position
    SET @inputData = STUFF(@inputData, @intPosition, 1, '' )   
    --PRINT @inputData 
    SET @intPosition = PATINDEX('%[^A-Za-z]%', @inputData )
    --Again get the position of the next integer in the input string
    --PRINT @intPosition 
END  
SELECT 'GEEKS PREMIER LEAGUE 2022' as InputString, @inputData AS AlphabetsOnly

输出：

第 7 步：单独获取数值假设当数据馈送发生时，包括员工姓名、电话号码、地址和电子邮件 id，我们可以使用以下方法检索下面的电话号码（即数值）方式。

询问：

DECLARE @inputString  VARCHAR(MAX)
DECLARE @validchars VARCHAR(MAX)

SET @inputString  = 'GeekAuthor1 123456789 Address1 geek@gmail.com'
--We are going to take continuous set of numbers
 and it should not have any spaces also in between
SET @validchars = '[0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]'
DECLARE @idx INT
SET @idx = PATINDEX('%'+ @validchars +'%',@inputString )
IF @idx > 0 AND 
    (@idx = LEN(@inputString )-8
    OR PATINDEX(SUBSTRING(@inputString ,@idx+9,1),'[0-9]')=0)
    SET @inputString =SUBSTRING(@inputString,
    PATINDEX('%'+ @validchars +'%',@inputString ), 9)
ELSE SET @inputString  = ''
SELECT @inputString as NumericAlone

因此，正则表达式在许多地方用于验证电子邮件、地址、单独验证 alpha 或单独验证数字。