在MySQL查询中获取NULL值

Question

我有两张像这样的表：

表gene_names：

+------------------+------------------+
| gene_alias       | gene_name        |
+------------------+------------------+
| AC148152.3_FG007 | AC148152.3_FG007 |
| AC149829.2_FG002 | AC149829.2_FG002 |
| AC149829.2_FG004 | AC149829.2_FG004 |
| AC155352.2_FG009 | AC155352.2_FG009 |
| AC155352.2_FG012 | AC155352.2_FG012 |
+------------------+------------------+

另一个名为gene_transcripts的表：

+-------------------+------------------+
| transcript_alias  | gene_alias       |
+-------------------+------------------+
| AC148152.3_FGT007 | AC148152.3_FG007 |
| AC149829.2_FGT002 | AC149829.2_FG002 |
| AC149829.2_FGT004 | AC149829.2_FG004 |
| AC155352.2_FGT009 | AC155352.2_FG009 |
| AC155352.2_FGT012 | AC155352.2_FG012 |
+-------------------+------------------+

我想要的是从gene_alias获取gene_transcripts和从gene_name获取gene_names。为此，我做（例子）：

SELECT gene_transcripts.gene_alias,
       gene_names.gene_name
FROM gene_transcripts,
     gene_names
WHERE gene_transcripts.gene_alias="AT4G38300_oG.1"
  AND gene_transcripts.gene_alias=gene_names.gene_alias;

它没有结果，因为gene_alias“AT4G38300_oG.1”在表gene_names中没有条目。到目前为止，它似乎非常合乎逻辑和合理。

我想得到什么（我不知道如何实现这个，因此我在这里问这个问题），是如何获得以下输出：

+-------------------+------------------+
| transcript_alias  | gene_alias       |
+-------------------+------------------+
| AT4G38300_oG.1    | NULL             |
+-------------------+------------------+

这可能吗？

Answer 1

只使用左连接

select 
   gt.gene_alias as transcript_alias, 
   gn.gene_name as gene_alias 
from gene_transcripts gt
left join gene_names gn on gt.gene_alias=gn.gene_alias
where gt.gene_alias="AT4G38300_oG.1"

Answer 2

SELECT gene_transcripts.gene_alias,
       gene_names.gene_name
FROM gene_transcripts,
     gene_names
WHERE (gene_transcripts.gene_alias="AT4G38300_oG.1"
  AND gene_transcripts.gene_alias=gene_names.gene_alias) 
  OR gene_transcripts.gene_alias IS NULL;