Question

我有这段代码：

select transcript_features.*,
    transcript_features_blast.hit, transcript_features_blast.evalue,
    transcript_features_blast.swissprot_version, 
    transcript_features_premirna_family.family, transcript_features_premirna_family.evalue,
    transcript_features_premirna_family.rfam_version, 
    transcript_features_premirna_homology.hit, transcript_features_premirna_homology.evalue,
    transcript_features_premirna_homology.mirbase_version,
    transcript_features_premirna.premirna, 
    transcript_features_transposons.hit, transcript_features_transposons.dfam_version, 
    confidence.confidence, expression.expression, expression.tissue, expression.conditions
from transcript_features_premirna, gene_transcripts, transcript_features_transposons, confidence, transcript_features
left join transcript_features_blast on transcript_features_blast.transcript_alias=transcript_features.transcript_alias
left join transcript_features_premirna_family on transcript_features_premirna_family.transcript_alias=transcript_features.transcript_alias
left join transcript_features_premirna_homology on transcript_features_premirna_homology.transcript_alias=transcript_features.transcript_alias
left join expression on expression.transcript_alias=transcript_features.transcript_alias
where transcript_features.transcript_alias=gene_transcripts.transcript_alias and gene_transcripts.gene_alias="AT1G19392" and transcript_features_premirna.transcript_alias=transcript_features.transcript_alias and transcript_features_transposons.transcript_alias=transcript_features.transcript_alias and confidence.transcript_alias=transcript_features.transcript_alias;

此代码工作正常。然而，当我引入一个额外的left join：

时

select transcript_features.*,
    transcript_features_blast.hit, transcript_features_blast.evalue,
    transcript_features_blast.swissprot_version, 
    transcript_features_premirna_family.family, transcript_features_premirna_family.evalue,
    transcript_features_premirna_family.rfam_version, 
    transcript_features_premirna_homology.hit, transcript_features_premirna_homology.evalue,
    transcript_features_premirna_homology.mirbase_version,
    transcript_features_premirna.premirna, 
    transcript_features_transposons.hit, transcript_features_transposons.dfam_version, 
    confidence.confidence, expression.expression, expression.tissue, expression.conditions
from transcript_features_premirna, gene_transcripts, transcript_features_transposons, confidence, transcript_features
left join transcript_features_blast on transcript_features_blast.transcript_alias=transcript_features.transcript_alias
left join transcript_features_premirna_family on transcript_features_premirna_family.transcript_alias=transcript_features.transcript_alias
left join transcript_features_premirna_homology on transcript_features_premirna_homology.transcript_alias=transcript_features.transcript_alias
left join expression on expression.transcript_alias=transcript_features.transcript_alias
left join transcript_names on transcript_names.transcript_alias=transcript_features.transcript_alias
where transcript_features.transcript_alias=gene_transcripts.transcript_alias and gene_transcripts.gene_alias="AT1G19392" and transcript_features_premirna.transcript_alias=transcript_features.transcript_alias and transcript_features_transposons.transcript_alias=transcript_features.transcript_alias and confidence.transcript_alias=transcript_features.transcript_alias;

永恒，永远不会结束。为什么？如果我删除一个随机left join，它可以很好地工作，并且我得到的结果不到0.30秒。也许，left join s太多了？

使用explain：

的输出

+----+-------------+---------------------------------------+--------+---------------+---------+---------+---------------------------------------------+-------+-------------+
| id | select_type | table                                 | type   | possible_keys | key     | key_len | ref                                         | rows  | Extra       |
+----+-------------+---------------------------------------+--------+---------------+---------+---------+---------------------------------------------+-------+-------------+
|  1 | SIMPLE      | confidence                            | ALL    | PRIMARY       | NULL    | NULL    | NULL                                        | 75858 |             |
|  1 | SIMPLE      | transcript_features                   | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.confidence.transcript_alias          |     1 |             |
|  1 | SIMPLE      | transcript_features_blast             | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.confidence.transcript_alias          |     1 |             |
|  1 | SIMPLE      | transcript_features_premirna_family   | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.confidence.transcript_alias          |     1 |             |
|  1 | SIMPLE      | transcript_features_premirna_homology | ALL    | NULL          | NULL    | NULL    | NULL                                        |  9530 |             |
|  1 | SIMPLE      | expression                            | ALL    | NULL          | NULL    | NULL    | NULL                                        | 75844 |             |
|  1 | SIMPLE      | transcript_names                      | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.transcript_features.transcript_alias |     1 | Using index |
|  1 | SIMPLE      | transcript_features_transposons       | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.transcript_features.transcript_alias |     1 | Using where |
|  1 | SIMPLE      | transcript_features_premirna          | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.transcript_features.transcript_alias |     1 | Using where |
|  1 | SIMPLE      | gene_transcripts                      | eq_ref | PRIMARY       | PRIMARY | 42      | GreeNC.transcript_features.transcript_alias |     1 | Using where |
+----+-------------+---------------------------------------+--------+---------------+---------+---------+---------------------------------------------+-------+-------------+

Answer 1

编写此查询的更合适的方法可能如下：

SELECT f.*
     , b.hit b_hit
     , b.evalue b_evalue
     , b.swissprot_version
     , pf.family
     , pf.evalue pf_evalue
     , pf.rfam_version
     , ph.hit ph_hit
     , ph.evalue ph_value
     , ph.mirbase_version
     , p.premirna
     , t.hit t_hit
     , t.dfam_version
     , c.confidence
     , e.expression
     , e.tissue
     , e.conditions
  FROM transcript_features f
  JOIN gene_transcripts gt
    ON gt.transcript_alias = f.transcript_alias 
  JOIN transcript_features_premirna p
    ON p.transcript_alias = f.transcript_alias 
  JOIN transcript_features_transposons t
    ON t.transcript_alias = f.transcript_alias 
  JOIN confidence c
    ON c.transcript_alias = f.transcript_alias
  LEFT 
  JOIN transcript_features_blast b
    ON b.transcript_alias = f.transcript_alias
  LEFT
  JOIN transcript_features_premirna_family pf
    ON pf.transcript_alias = f.transcript_alias
  LEFT
  JOIN transcript_features_premirna_homology ph 
    ON ph.transcript_alias = f.transcript_alias
  LEFT
  JOIN expression e 
    ON e.transcript_alias = f.transcript_alias
 WHERE gt.gene_alias = "AT1G19392";

MySQL中左连接的时间问题

1 个答案: