--连接查询 左链接、右链接,全链接
--内链接
select e.account 用户名, e.empname 名称, c.comname 公司名称
  from employee e
 inner join company c on (e.com_sq = c.sequen)
 where c.sequen = 1;
--连接查询也可以用这种方法来查询
select e.account 用户名, e.empname 名称, c.comname 公司名称
  from employee e,company c where e.com_sq=c.sequen;

JOIN的写法是SQL的标准,当有多个表关联时,JOIN的方式写法的写法能更清楚的看清楚各表之间的关系,所以建议使用JSON写法

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left join 以左边查询为准,只会返回左边匹配的数据,右表没有匹配的信息不显示
aaarticlea/png;base64,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" alt="" /> right join 以右边查询为准,只会返回左右边匹配的数据,左表没有匹配的信息不显示
aaarticlea/png;base64,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" alt="" /> full join 全查询,左右两表数据都显示出来
aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAzoAAACiCAIAAAAGDi9QAAAQY0lEQVR4nO3dQXLjOBIFUF2g7tN3np7VXKyjtrPQLKpbwyISiQRFyRD9XjgcMggCICWCn5Rl3/76668///zz/o9//fs/dwAAlnET1wAAViauAQAsTVwDAFiauAYAsDRxDQBgaeIaAMDSxDUAgKWJawAASxPXAACWJq4BACxNXAMAWJq4BgCwNHHtI91utycrXMN2M5/c5Pou/Sb7lg/iNVlkR/G51o1rt3989UDe4daXrJI3+IJhLiePa1N7tbfH2lWm9u01XsPJVoT7p77VLjyed8ou6h0U19v/19sivolBXGvPcPmPj8LTxvc9Dq1eGmh3bCV/FAPKBRxLUW3Nyi7tVa509NH7v7IV4S6davxwBV4X185qfCnX2yK+iSyutefC8OwYvvrPOiSOtfNxB2Q9rk2tPlzxo+URIcm1lb3aq1N8RipLP0VlKw7HNZ706v18yefxkhvF5VXjWlsyvOZ+6TXfK9b6Qr1sMRvX6nHkAtpX4IE7OsM9Fj4d4Vp5R59LXFvZV8W1fKZa3GeNFn4pvRm6/bF9nLz080XtcV4JKGGd3am0MoNUpphKs7N1eh0NH7c/JuWPPFGcmOp7rPd8tdv+5Xvs1mjr7Fbs9Vt8ItpNeDTYPthWC1cZNt5b61g7T25Fu2Leddh7snPawVSGHTZV32OVtXrbko+nV+fAlibtFMcTrlIcwNCwnXBje8/F7YyjqW354LbBG5U+arA9APLC3oqVRXkvvTqVtZLeKyOsP2i/z/aVb8itr22wPgedsjeK237KHsuf697qebPJHtudJ9oB94RPXzKkYuOnv+ryDansxuEZsdL4sRkgafPc12rxQWU8B8Y8XPHJ8cy2M5yCDownWevcZ6c+N8I6qp8MfUxtu/PWPT2eB33/fpCHR354wtvWCXspdp3MMnlf4bDvm720qzzVVzIJVnZ1salKs3md3d7obXsywmSt4Zgrg+/tvbY832Pb0fY2cGoAvSGFeyNstrIPhyMs7ufKbkw2LRc2krRc3K5eyTOv1bzy1HiSOlMtt0srz2m46MB+rqi/DMLdPrXnK2tNjQqWcvCjBuEhcT90kOerzJ7wir1PTaBJX1OngWJflXNVr5Fd1/ngK4uSOsdOgWftsbZmsl3JGIZ7LBzb4VNpr0KyN4rNDvf8sJ3ZrZja+ZXGKy1/4Ws1GWHxZfDMmCvtVyr3Wj6wnyuOTYMH5t7iWsWRwIIGce2hLWzr5Ce/fcejxttmwwE8SsLGKwN4/JjXaR+He+DRVD7mtqOpx7netuRLh3319vN2ld331+2xcJC9l8Hwuc73WDvCfGe2vSdblO/DYeO9tSo7sFKt3Xv3aMeGW1ocQNtdb3htL/mweyX1PZZvY28rKuPJ69S3tO293WnD8Qy3PR95brivwo6mSpL91u7DcADPbCC8x8E/k/v8McxWbzqbOiVsa4amGllcbxsreyw/YVSaWn83rj/CX9YZ5+GRrLAJK4zhPZ7c0nD177P3+Gjr/leD76M3g+RXhAcaPDa8z5JsZhvC8rWS3Lz4zky2dBGrjfDYeJbahO9gtZcNvJO4BgCwNHENAGBp4hoAwNLENQCApYlrAABLE9cAAJYmrgEALE1cAwBYmrgGALA0cQ0AYGniGgDA0sQ1AICliWsAAEsT1wAAlnZyXLvdbk9WAOAZ22n2ySm3PqWb2+GlBnHt1tdtMT1oHdIAL5XHtalZvTdjt6uY2+GlxnFt+PhePv6nYh8ABxxLUcVgl3RkYofXOS2uxa2PZg1HNcCJwtS1fdwLYZVZvVeneEYADjvnzdBhXKtPBwAc1kao4kzbXl3P3ksL1wJO8b67a9sSd8sBTleZsXvX3snttN6M7Qoc3uatv7t2F9QAXiOZorclxTc0H4XJ1fhjafsdONeb3gytNwXAk5J5tRjXhjP2NqvtgppZHU732jdDH0uTqy4HNsCJirfZdj+GOazXeJjPxDV4nRPiWv3IFNcAXqqSz3p3y4ZN3aPJPwx8xzcAiLw7rnkzFOBFhu9g3ic/GTbVlMkcXieLa71Lq/yCLOvM3TWAt0um2eSyuXh3bdvOc8MEuvyLdwCApYlrAABLE9cAAJYmrgEALE1cAwBYmrgGALC0wR/yAGBBwWwOXJi7awAAKxPXAACWJq4BACxNXAMAWJq4BgCwNHENAGBp4hoAwNIGce32z1/3Cf8ISNBcVNguSqoB8LzeNHvirH4vT+zJYLZd54NxEuE7G99da4+QA8dk2A4AL5JMufmsPvxrncVeetXC8nAY9S3Kh90bFXyQ6puhT16HhVdOjiWAE03Nsb2a+Zxcj2tJfmr7artuh5EvLQ4YPtREXAu/h9WG5Y4fgJcaZq/hrL7LUkkjebXiGO7pm6HD9HYsfcKnKP3P0HvnYOiVh3V2bYYHJACnCCfYyqy+q39Po9Itimu3WpBq2w9b6zVePH04y3ANE7+7lhxIs+WOH4BzVS6eHzV3D+7pLB3O2G2SC0uSddsHvU6Lj5NECJ9uLq4lF2H36HhrF+WTCADPy+fV4qw+TDxtCgzTWzLtt3Etz1v1QYprXMyZd9eGcS380bEEcKI2e1WiTC/D5RfYxfNCr7CNa73hJa3VtxE+12l314oXQJXKABzTJp78jlQyq+8qD5f2klmS+ZK4dtZZximGayjFtUq6EtcAvlabw9pF9/Ks3jaYVOi1M7y7lqS3vJ32tJInQvho1btryeXRfTKf7do8YysAvrv6nFyc1Wcz07G4tisPF4VDHZ6G8nL4LNP/MzQ5utqayTF5ZLAA1CTJpq3ZrphXTvLTMEXVTw3DM0U+znxD4LP4F+8AAEsrxbX6BUrxAs4VD8CLzL5F+Lhh9vixeOesbT+8l5b/eOAunRMN39BcXBseCY4igC9UCUy7PLSb4fP5+VEnfE/zQFwrbsvuce+9zvxEU8ygsKBBXGtfzclh2Su8N0e44wTgdPkM3Cs5K0IlHfVm/mJfeafF7ap0BMuafjM0P8aK5Y4NgHNVglFye2lbM4lHU2mpvSZvzwXDvrahbbctSe/5eKZSI6zg2bg2e/CHFQA4UR6qksr33yf55Hs4kw8j1DN9Je3sCpPxVPYALCiLa/UDcrtKpdyxAfAiU8nm/ns2Ch8MC9tG2vL8bPJ8X3nlx+PZkxos4sgnQ/NMlkwN7aHSXjMBcMxuRg1vSrXT77G4Fk7gYVxrTw0H+so3sJfPkl6ScljQ+KMG9+hIyDNZb1H4o+ME4M2SWb3NcL1UF54gtuW9O1hTfbXhcleSbFq+SFzjg1TjWntkTiUwcQ3g1W59YbVtyW5pviiMbmF+apua7WvY4LGld3GNjzJ3dy05EsQ1gK+1m6uTqTus0MappIuw5tTkP9tXmPZmew9TrNMQ66v+3bVBK4cO0UrLABQN41oe4F4d14Z5K1y3vQMX3sxro1hYZ7hRsKbBJ0MfD3rHQBK5kmsXxwbAuZK80k7UeW7L228b6ZX0zhTb8mJfYReVU0lSJ+kFVuNfvAMALG3in1Dl12qP+uMuXcoAvEzl/lNyU+3YXbped8P6xb6KN9Vm773Bpyh91CB/ENbfFc7GPgAOqASm3fS7m9XzOflRZzt7J+eF2XjXW7p73Dt95HHNaYjP9Y64dqAOALN6s+tUrDkcoZKOegmp2FfeaXG7Kh3Bst70ZqhrGoCXqgSjfErf1tk1+3g8lZbaef7WRMNhX7dNaNttS9J7Pp5w58DKjvwTqt2i4cFfbw2A5+WhKql8/z0MJd/DqX4YoZ7pK2lnV5iMp7IHYEHPxrVKzQORDoBjppLN/fdsFD4YFraNtOV5vHu+r7zy43ExZcJqqnGtkrF6h+t2aV4CwGG7yTm8KdXO5MfiWnguCOf59tRwoK98A3v5LOklKYcFjeNakszCwiSuVTIfAK/W5ptddsm/3/tRaVu+neeTQDb8HjbbO4kkZxZxjc819z9Dt4X7hka/KpFc8QDwvPCquI01bWEbufJFYXQL81OSC4t9DRs8tvQurvFRqv/VYHtZk1RoH28L8xkEgGfs8kcYR3p5qy3Muwhr1hNSr37SV5j2ZnsPz0FORqxvIq4lL+gDB21YAsBhw7iWB7hXx7Vh3grXbe/Ahdf84R2Bts5wo2BNg3/xPrwNlizNj5O8WQCmJHmlnW/z3Ja33zbSK9lGwDZaTfUVdlE5iQzPX85EfAT/4h0AYGnTf3ctvxApLnU1AzDrv3/84esyX1/9auLDHP8nVHFzk3FNbgMoco6/DE8ls953d63+GxIAtJzjL8NTyazqRw2KN9jy3xvt/QjAkHP8ZXgqmTXxUYNePhtGut33NrqduD0AV+UcfxmeSma973fXehFNXAOocI6/DE8ls0r/hCp/vCssJrlh8gNgyzn+MjyVzDrz7loe13bVAJjiHH8ZnkpmnXZ3LVla+f02AHLO8ZfhqWTWaXfX6r+OJp8BHOAcfxmeSmaNPxmaJ7N6SWURAD3O8ZfhqWTWxJuhYXn+KdHkV9wAmPLl/zfJ14lfX/1q4sNM/N21L39x+8q/3vKCAQDebS6uvWVIHOHZAbaK740UP/g1bC2pU5cPoDja/A2fx4pn/TY2vIe4dhGeHWArCRztol1Jm2x2K4bhKc9Dw7DVjqQ35l5JsTzc5KSRcGlxo+As4tpFeHaAqQyR17ylAa5XLR9bPuzej73VkxGG23U7L64lG1KsCbPEtYvw7ABbbShJKuy+J1FvmLrCCnlkDKsli5I2i9t7TzfzWDTMe4cniWsX4dkBtnpha5stkszRfr/3s06S0hJ5tUpTxe62g2+35d7ErHB7w53cDqBSDQ4Q1y7CswPfXJ6NwnSSFN42kS5c5cnck6wVlgyFAS7pujeA4uMkEcIriGsX4dkBHvLcsI0XYebYZbVtzV47YadhR+0Ih+FyVx6W9Nppe+w10o4q2ZxKOZxIXLsIzw7wS5Krdj+G6aQtHMaRYXnyIFy9t7TNhXk7SdfDTUuyl7jG+4lrF+HZAe6dX6gP6zyWtneYkttXvTrDG1r5faxKp0lJPqp2MOH3cBcNl7YtwyuIaxfh2QHaeNQuujcZrhc+kse7wmHoSR70Hic1D4zw3uyTJGNV8lmeCOF04tpFeHbgm6vfEHqEnt49rV4QGd5VGsaatuW28XZpZYThVg/HFu6c4oCTvuB04tpFeHaArSRttDV7P7YpbRuYeqv0ElLSS1uzl6XCkl53yWDyH/MBh73IaryUf/F+na+3vGAAgHebiGsAALyfuAYAsDRxDQBgaeIaAMDSxDUAgKWJawAASxPXAACWJq4BACxNXAMAWJq4BgCwNHENAGBp4hoAwNLENQCApWVx7efL/Pjx48ePH69rHwDgMsQ1AIClDeLabePvFdIfH4V5r+IaAEBRFte2qevX47bkZyec5YlNXAMAKKrGtb9rl+NaUv5TXAMAKCu9Gfr/2jNxLVkkrgEAFJU+ahAmM3ENAOANqp8Mffzu2uN+mzdDAQDe4OBHDXYfDt1V++mjBgAAJxnEtfbvdPT+kEd4461HXAMAKDr4Z3Lbv7U2RVwDACjyXw0AAJYmrgEALC2LawAAfDlxDQBgaeIaAMDSxDUAgKWJawAASxPXAACW9j8DjZEsI2XQlAAAAABJRU5ErkJggg==" alt="" />
其中左右链接查询也可以是下面哪种写法
select * from table1 a,table2 b from a.v(+)=b.id; --(+) 在右边表示有查询相当于 right join
select * from table1 a,table2 b from a.v=b.id(+); --(+) 在左边表示有查询相当于 left join
(+)操作符只能用于实现左外连接和右外连接,而不能用于实现完全外连接。
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" alt="" />

												

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