mysql查找重復字段的兩種方法。

為了查找字段是否重復的字段內容。

SELECT `Formats_text_url`, COUNT(*) as count FROM `home_page_info_update` GROUP BY `Formats_text_url` HAVING count>1;

　　

上面這條語句能夠查尋出重復字段的字段內容，但不能顯式全部字段的信息，所以做了改進

 

查尋字段重復內容
SELECT * FROM `home_page_info_update` 
		WHERE `Formats_text_url` IN 
					(SELECT `Formats_text_url` FROM `home_page_info_update` GROUP BY `Formats_text_url` HAVING COUNT(`Formats_text_url`)>1);

SELECT * FROM `home_page_info_update`
		INNER JOIN
				(SELECT `Formats_text_url` FROM `home_page_info_update` GROUP BY `Formats_text_url` HAVING COUNT(`Formats_text_url`)>1) AS tb2 USING(`Formats_text_url`);


查尋sec_insider_info_detail中的重復字段.
SELECT * FROM `sec_insider_info_detail`
    INNER JOIN
		     (SELECT `info_url` FROM `sec_insider_info_detail` GROUP BY `info_url` HAVING COUNT(`info_url`)>1) AS 
				 tb2 USING(`info_url`) ORDER BY `sec_insider_info_detail`.`reporteddatetime` DESC;

SELECT * FROM `sec_insider_info_detail`
    WHERE `info_url` IN
		     (SELECT `info_url` FROM `sec_insider_info_detail` GROUP BY `info_url` HAVING COUNT(`info_url`)>1);

　　

上面分別通過兩種方式選出重復字段的所有字段信息，一種采用子查尋集，然后通過IN的方式查出需要的查尋結構。

一種通過將子查詢定義成一份新的表數據，通過兩個表的連表查尋來顯式需要的結果。[會稍微多一些字段信息]

 

兩種方式，第二種方式的查尋效果快很多，推薦第二種使用連表查尋。