标签：多表 author 菜鸟 runoob 关联 RUNOOB COM 查询 +-------------+-----------------+----------
1 连接种类 2 INNER JOIN（内连接,或等值连接）：获取两个表中字段匹配关系的记录。 3 LEFT JOIN（左连接）：获取左表所有记录，即使右表没有对应匹配的记录。 4 RIGHT JOIN（右连接）： 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录 5 OUT JOIN 全连接 将左边表数据和右边表数据全部匹配出来 6 --------------------------------------------------------------------------------------- 7 --------------------------------------------------------------------------------------- 8 9 -- 示例 10 SELECT * FROM tcount_tbl; 11 +---------------+--------------+ 12 | runoob_author | runoob_count | 13 +---------------+--------------+ 14 | 菜鸟教程 | 10 | 15 | RUNOOB.COM | 20 | 16 | Google | 22 | 17 +---------------+--------------+ 18 SELECT * from runoob_tbl; 19 +-----------+---------------+---------------+-----------------+ 20 | runoob_id | runoob_title | runoob_author | submission_date | 21 +-----------+---------------+---------------+-----------------+ 22 | 1 | 学习 PHP | 菜鸟教程 | 2017-04-12 | 23 | 2 | 学习 MySQL | 菜鸟教程 | 2017-04-12 | 24 | 3 | 学习 Java | RUNOOB.COM | 2015-05-01 | 25 | 4 | 学习 Python | RUNOOB.COM | 2016-03-06 | 26 | 5 | 学习 C | FK | 2017-04-05 | 27 +-----------+---------------+---------------+-----------------+ 28 29 --------------------------------------------------------------------------------------- 30 --------------------------------------------------------------------------------------- 31 32 INNER JOIN（内连接,或等值连接）：获取两个表中字段匹配关系的记录 33 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a 34 INNER JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; 35 +-------------+-----------------+----------------+ 36 | a.runoob_id | a.runoob_author | b.runoob_count | 37 +-------------+-----------------+----------------+ 38 | 1 | 菜鸟教程 | 10 | 39 | 2 | 菜鸟教程 | 10 | 40 | 3 | RUNOOB.COM | 20 | 41 | 4 | RUNOOB.COM | 20 | 42 +-------------+-----------------+----------------+ 43 -- 也可以这样使用 44 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a, tcount_tbl b WHERE a.runoob_author = b.runoob_author; 45 +-------------+-----------------+----------------+ 46 | a.runoob_id | a.runoob_author | b.runoob_count | 47 +-------------+-----------------+----------------+ 48 | 1 | 菜鸟教程 | 10 | 49 | 2 | 菜鸟教程 | 10 | 50 | 3 | RUNOOB.COM | 20 | 51 | 4 | RUNOOB.COM | 20 | 52 +-------------+-----------------+----------------+ 53 --------------------------------------------------------------------------------------- 54 --------------------------------------------------------------------------------------- 55 56 LEFT JOIN（左连接）：获取左表所有记录，即使右表没有对应匹配的记录。 57 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a LEFT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; 58 +-------------+-----------------+----------------+ 59 | a.runoob_id | a.runoob_author | b.runoob_count | 60 +-------------+-----------------+----------------+ 61 | 1 | 菜鸟教程 | 10 | 62 | 2 | 菜鸟教程 | 10 | 63 | 3 | RUNOOB.COM | 20 | 64 | 4 | RUNOOB.COM | 20 | 65 | 5 | FK | NULL | 66 +-------------+-----------------+----------------+ 67 68 -- 也可以这样 69 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a, tcount_tbl b WHERE a.runoob_author = b.runoob_author(+); （+在那边就显示那边的null） 70 +-------------+-----------------+----------------+ 71 | a.runoob_id | a.runoob_author | b.runoob_count | 72 +-------------+-----------------+----------------+ 73 | 1 | 菜鸟教程 | 10 | 74 | 2 | 菜鸟教程 | 10 | 75 | 3 | RUNOOB.COM | 20 | 76 | 4 | RUNOOB.COM | 20 | 77 | 5 | FK | NULL | 78 +-------------+-----------------+----------------+ 79 --------------------------------------------------------------------------------------- 80 --------------------------------------------------------------------------------------- 81 82 83 RIGHT JOIN（右连接）： 与 LEFT JOIN 相反，用于获取右表所有记录，即使左表没有对应匹配的记录 84 85 RIGHT JOIN 86 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a RIGHT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; 87 +-------------+-----------------+----------------+ 88 | a.runoob_id | a.runoob_author | b.runoob_count | 89 +-------------+-----------------+----------------+ 90 | 1 | 菜鸟教程 | 10 | 91 | 2 | 菜鸟教程 | 10 | 92 | 3 | RUNOOB.COM | 20 | 93 | 4 | RUNOOB.COM | 20 | 94 | NULL | NULL | 22 | 95 +-------------+-----------------+----------------+ 96 -- 也可以这样 97 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a , tcount_tbl b ON a.runoob_author(+) = b.runoob_author; 98 +-------------+-----------------+----------------+ 99 | a.runoob_id | a.runoob_author | b.runoob_count | 100 +-------------+-----------------+----------------+ 101 | 1 | 菜鸟教程 | 10 | 102 | 2 | 菜鸟教程 | 10 | 103 | 3 | RUNOOB.COM | 20 | 104 | 4 | RUNOOB.COM | 20 | 105 | NULL | NULL | 22 | 106 +-------------+-----------------+----------------+ 107 --------------------------------------------------------------------------------------- 108 --------------------------------------------------------------------------------------- 109 110 OUT JOIN 全连接 111 SELECT a.runoob_id, a.runoob_author, b.runoob_count FROM runoob_tbl a OUT JOIN tcount_tbl b ON a.runoob_author = b.runoob_author; 112 +-------------+-----------------+----------------+ 113 | a.runoob_id | a.runoob_author | b.runoob_count | 114 +-------------+-----------------+----------------+ 115 | 1 | 菜鸟教程 | 10 | 116 | 2 | 菜鸟教程 | 10 | 117 | 3 | RUNOOB.COM | 20 | 118 | 4 | RUNOOB.COM | 20 | 119 | 5 | FK | NULL | 120 | NULL | NULL | 22 | 121 +-------------+-----------------+----------------+ 122 --------------------------------------------------------------------------------------- 123 ---------------------------------------------------------------------------------------
标签：多表,author,菜鸟,runoob,关联,RUNOOB,COM,查询,+-------------+-----------------+---------- 来源： https://www.cnblogs.com/chendakeng/p/15978818.html
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