简短摘要：在Drupal环境中运行，我有一个查询，它返回一个空结果集，除非我对内部选择的结果运行某种命令。这可以是Trim，replace，upper。
所有不需要的字段都已从select中删除，因此我只剩下查询的相关部分。
mysql> SELECT HEX(taxonomy_term_field_data_node_field_data.name)
FROM node_field_data
LEFT JOIN (SELECT td.*, tn.nid AS nid
FROM taxonomy_term_field_data td
LEFT JOIN taxonomy_index tn ON tn.tid = td.tid
WHERE (td.vid IN ('category'))
) taxonomy_term_field_data_node_field_data
ON node_field_data.nid = taxonomy_term_field_data_node_field_data.nid
WHERE (taxonomy_term_field_data_node_field_data.name = "Politik");
Empty set (0.01 sec)
当taxonomy_term_field_data表不在联接中时（其中名称=＆＃34; Politik＆＃34;）可以从mysql> SELECT name FROM taxonomy_term_field_data WHERE name = "Politik";
+---------+
| name |
+---------+
| Politik |
+---------+
1 row in set (0.00 sec)
表中进行选择？
mysql> SELECT HEX(taxonomy_term_field_data_node_field_data.name)
FROM node_field_data
LEFT JOIN (SELECT td.*, tn.nid AS nid
FROM taxonomy_term_field_data td
LEFT JOIN taxonomy_index tn ON tn.tid = td.tid
WHERE (td.vid IN ('category'))
) taxonomy_term_field_data_node_field_data
ON node_field_data.nid = taxonomy_term_field_data_node_field_data.nid
WHERE (REPLACE(taxonomy_term_field_data_node_field_data.name, "", "") = "Politik");
+----------------------------------------------------+
| HEX(taxonomy_term_field_data_node_field_data.name) |
+----------------------------------------------------+
| 506F6C6974696B |
| 506F6C6974696B |
| 506F6C6974696B |
+----------------------------------------------------+
3 rows in set (0.01 sec)
如果我在查询中没有替换任何内容，我会得到结果： 这也可以在字符串或TRIM上使用UPPER。
taxonomy_term_field_data table我还尝试在mysql> explain SELECT taxonomy_term_field_data_node_field_data.name FROM node_field_data LEFT JOIN (SELECT td.*, tn.nid AS nid FROM taxonomy_term_field_data td LEFT JOIN taxonomy_index tn ON tn.tid = td.tid WHERE (td.vid IN ('category')) ) taxonomy_term_field_data_node_field_data ON node_field_data.nid = taxonomy_term_field_data_node_field_data.nid WHERE (trim(taxonomy_term_field_data_node_field_data.name) = "Politik");
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-------------+
| 1 | PRIMARY | node_field_data | index | PRIMARY,node__id__default_langcode__langcode | node__vid | 4 | NULL | 20 | Using index |
| 1 | PRIMARY | <derived2> | ref | <auto_key0> | <auto_key0> | 5 | v15x.node_field_data.nid | 14 | Using where |
| 2 | DERIVED | td | ALL | taxonomy_term__tree,taxonomy_term__vid_name | NULL | NULL | NULL | 1404 | Using where |
| 2 | DERIVED | tn | ref | term_node | term_node | 4 | v15x.td.tid | 1 | Using index |
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-------------+
4 rows in set (0.00 sec)
mysql> explain SELECT taxonomy_term_field_data_node_field_data.name FROM node_field_data LEFT JOIN (SELECT td.*, tn.nid AS nid FROM taxonomy_term_field_data td LEFT JOIN taxonomy_index tn ON tn.tid = td.tid WHERE (td.vid IN ('category')) ) taxonomy_term_field_data_node_field_data ON node_field_data.nid = taxonomy_term_field_data_node_field_data.nid WHERE (taxonomy_term_field_data_node_field_data.name = "Politik");
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-----------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-----------------------+
| 1 | PRIMARY | node_field_data | index | PRIMARY,node__id__default_langcode__langcode | node__vid | 4 | NULL | 20 | Using index |
| 1 | PRIMARY | <derived2> | ref | <auto_key1> | <auto_key1> | 5 | v15x.node_field_data.nid | 14 | Using index condition |
| 2 | DERIVED | td | ALL | taxonomy_term__tree,taxonomy_term__vid_name | NULL | NULL | NULL | 1404 | Using where |
| 2 | DERIVED | tn | ref | term_node | term_node | 4 | v15x.td.tid | 1 | Using index |
+----+-------------+-----------------+-------+----------------------------------------------+-------------+---------+--------------------------+------+-----------------------+
4 rows in set (0.00 sec)
中更新名称=修剪（名称），但这不起作用。
其中一个查询使用where和另一个条件索引，但是如何解决这个问题的任何输入都非常受欢迎。
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