如何从连接结果中排除 NULL 行 [英] How do I exclude NULL rows from join result

问题描述

下面是我想从中生成输出表的表 t1 和 t2.我的努力是不在输出中包含 y1 为 NULL 的行.

Below are the tables t1 and t2 that I want to generate the output table from. My struggle was to not include in the output the rows where y1 is NULL.

+--------------+  +--------------+  
|      t1      |  |      t2      | 
+--------------+  +--------------+
| x0 | x1 | x2 |  |  x0  |   y1  |    
+--------------+  +--------------+
| a  | 10 | a  |  |  a   |  haha |
| b  | 11 |NULL|  |  b   |  NULL |
| c  | 12 | c  |  |  c   |  foo  |
| d  | 13 |NULL|  |  d   |  NULL |
+--------------+  + -----+-------+

+--------------+
|    output    |
+--------------+
|  x0  |  y1   |
+--------------+
|  a   |  haha |
|  c   |  foo  |
+--------------+

我试过了:

SELECT t1.x2, t2.y1
FROM t1
LEFT JOIN t2 ON t1.x0 = t2.x0

另外:在某些情况下，我的行不显示 NULL 而只是空单元格.

Also: In some cases my rows don't say NULL but are just empty cells.

推荐答案

您需要:

SELECT t1.x2, t2.y1
FROM t1
LEFT JOIN t2 ON t1.x0 = t2.x0
WHERE y1 IS NOT NULL AND y1 <> ''

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