I have a table of tags that can be linked to other tags and I want to "recursively" select the tags in order of arrangement. So that when a search is made, we get the immediate (1-level) results and then carry on down to say 5-levels so that we always have a list of tags no matter if there wasn't enough exact matches on level 1.
I can manage this fine with making multiple queries until I get enough results, but surely there is a better, optimized, way via a one-trip query?
Any tips will be appreciated. Thanks!
Results:
tagId, tagWord, child, child tagId
'513', 'Slap', 'Hog Slapper', '1518'
'513', 'Slap', 'Corporal Punishment', '147'
'513', 'Slap', 'Impact Play', '1394'
Query:
SELECT t.tagId, t.tagWord as tag, tt.tagWord as child, tt.tagId as childId
FROM platform.tagWords t
INNER JOIN platform.tagsLinks l ON l.parentId = t.tagId
INNER JOIN platform.tagWords tt ON tt.tagId = l.tagId
WHERE t.tagWord = 'slap'
Table Layouts:
mysql> explain tagWords;
+---------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------------+------+-----+---------+----------------+
| tagId | bigint(20) unsigned | NO | PRI | NULL | auto_increment |
| tagWord | varchar(45) | YES | UNI | NULL | |
+---------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
开发者_StackOverflowmysql> explain tagsLinks;
+----------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+---------------------+------+-----+---------+-------+
| tagId | bigint(20) unsigned | NO | | NULL | |
| parentId | bigint(20) | YES | | NULL | |
+----------+---------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
AFAIK Mysql doesn't have any mechanism for querying data recursively
Oracle has Connected By
construct and Sql Server has CTE(Common Table Expressions)
.
But Mysql, Read Here and Here
Here are the options that I consider each time I find myself in a situation when I need to query hierarchical data.
- Nested Sets
- Path enumeration
- Explicit joins (when the maximum level is known)
- Vendor Extensions (SQL Server CTE, Oracle Connect by etc)
- Stored Procedures
- Suck it up
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