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MySQL databaseJoang ho sebetsana le lipotso tsa boleng ba non-null?MySQL ha se polelo ea khetho e fosahetseng
Ho se sebetse hantle ho MySQL
Re se re ntse re tseba hore MySQL e sebelisa taelo ea SQL SELECT le karolo ea WHERE ho bala lintlha tse tafoleng ea data, empa ha tšimo ea boemo ba potso e fanoeng ke NULL, taelo e ka 'na ea se ke ea sebetsa hantle.
Ho sebetsana le boemo bona, MySQL e fana ka lits'ebetso tse tharo tse kholo:
- HA E NTLE:Opereishene ena e khutlisa 'nete ha boleng ba kholomo e le NULL.
- HASE LEFEELA:Opereishene e khutlisa 'nete ha boleng ba kholomo e se NULL.
- <=>: Mokhanni oa papiso (ho fapana le = opareitara) o khutlela 'nete ha litekanyetso tse peli li bapisoa li le NULL.
Ts'ebetso ea papiso ea maemo ho NULL e khethehile.U ke ke ua sebelisa = NULL kapa ! = NULL e fumana litekanyetso tsa NULL kholomong.
Ho MySQL, papiso ea boleng ba NULL le boleng bofe kapa bofe (esita le NULL) e lula e khutlisa leshano, ke hore, NULL = NULL e khutlisa leshano.
NULL e sebetsoa ho MySQL ho sebelisoa IS NULL mme HA E NULL basebetsi.
Sebelisa boleng ba NULL ka potlako ea taelo
Mohlaleng o latelang, tafole chenweiliang_test_tbl polokelongtshedimosetso chenweiliang e behilwe ho ba le dikholomo tse pedi, chenweiliang_author le chenweiliang_count, mme boleng ba NULL bo behilwe ho kenngwa ho chenweiliang_count.
Mohlala
Leka mehlala e latelang:
Theha tafole ea lintlha chenweiliang_test_tbl
root @ host #mysql -u root -p password; 输入密码:******* mysql > 使用chenweiliang ; 数据库改变了mysql > create table chenweiliang_test_tbl - > ( - > chenweiliang_author varchar (40 )NOT NULL , - > chenweiliang_count INT - > ); 查询OK ,0 行受影响(0.05 秒)mysql > INSERT INTO chenweiliang_test_tbl (chenweiliang_author ,chenweiliang_count )values (' chenweiliang ' ,20 ); mysql > INSERT INTO chenweiliang_test_tbl (chenweiliang_author ,chenweiliang_count )values (' 陈沩亮博客' ,NULL ); mysql > INSERT INTO chenweiliang_test_tbl (chenweiliang_author ,chenweiliang_count )values ( ' Google ' ,NULL ); mysql > INSERT INTO chenweiliang_test_tbl (chenweiliang_author ,chenweiliang_count )values (' FK ' ,20 ); mysql > SELECT * from chenweiliang_test_tbl ; + --------------- + -------------- + | chenweiliang_author | chenweiliang_count | + --------------- + -------------- + | chenweiliang | 20 | | 陈沩亮博客| NULL | | Google | NULL | | FK | 20 | + --------------- + -------------- + 4 行中集合(0.01 秒)
Mohlaleng o latelang o ka bona = le ! The = opareitara ha e sebetse:
mysql > SELECT * FROM chenweiliang_test_tbl WHERE chenweiliang_count = NULL ; 空集(0.00 秒)mysql > SELECT * FROM chenweiliang_test_tbl WHERE chenweiliang_count != NULL ; 空集(0.01 秒)
Ho fumana hore na kholomo ea chenweiliang_test_tbl tafoleng ea data ke NULL, o tlameha ho e sebelisa.KE NULLleHA E NULL, mohlala o latelang:
mysql > SELECT * FROM chenweiliang_test_tbl WHERE chenweiliang_count IS NULL ; + --------------- + -------------- + | chenweiliang_author | chenweiliang_count | + --------------- + -------------- + | 陈沩亮博客| NULL | | Google | NULL | + --------------- + -------------- + 2 行中的组(0.01 秒)的MySQL > SELECT * 从chenweiliang_test_tbl WHERE chenweiliang_count IS NOT 空值 ; + --------------- + -------------- + | chenweiliang_author | chenweiliang_count | + --------------- + -------------- + | chenweiliang | 20 | | FK | 20 | + --------------- + -------------- + 2 行中的组(0.01 秒)
Ho sebetsana le litekanyetso tsa NULL ka PHP script
Sengoliloeng sa PHP, u ka sebelisa polelo ea haeba ...
Mohlaleng o latelang PHP e beha $chenweiliang_count e feto-fetohang ebe e sebelisa phapang eo ho bapisa le sebaka sa chenweiliang_count tafoleng ea data:
MySQL ORDER BY test:
<? php $ dbhost = ' localhost:3306 ' ; // mysql服务器主机地址 $ dbuser = ' root ' ; // mysql用户名 $ dbpass = ' 123456 ' ; // mysql用户名密码 $ conn = mysqli_connect ($ dbhost ,$ dbuser ,$ dbpass ); 如果(!$ conn ){ die (' 连接失败:' 。mysqli_error ($ conn )); } // 设置编码,防止中文乱码 mysqli_query ($ conn ,“ set names utf8 ” ); if (isset ($ chenweiliang_count )){ $ sql = “ SELECT chenweiliang_author,chenweiliang_count FROM chenweiliang_test_tbl WHER chenweiliang_count = $ chenweiliang_count ” ; } else { $ sql = “ SELECT chenweiliang_author,chenweiliang_count FROM chenweiliang_test_tbl WHER chenweiliang_count IS NULL ” ; } mysqli_select_db ($ conn ,' chenweiliang ' ); $ retval = mysqli_query ($ conn ,$ sql ); if (!$ retval ){ die (' 无法读取数据:' 。mysqli_error ($ conn )); } echo ' <h2>陈沩亮博客IS NULL测试<h2> ' ; echo ' <table border =“1”> <tr> <td>作者</ td> <td>登陆次数</ td> </ tr> ' ; $ retval ,MYSQL_ASSOC )){ echo “ <tr> ” 。 “ <td> {$ row ['chenweiliang_author']} </ td> ” 。 “ <td> {$ row ['chenweiliang_count']} </ td> ” 。 “ </ tr> ” ; } echo ' </ table> ' ; mysqli_close ($ conn ); ?>
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