[英]mySQL >> Very Slow Query with CONCAT, GROUP_CONCAT and multiple JOINS (100 sec for 63 records)
我正在使用以下查詢：
SELECT *,
GROUP_CONCAT(distinct t_name order by t_id separator ', ') 'Topics',
GROUP_CONCAT(distinct ch_title order by ch_id separator ', ') 'Chapters',
GROUP_CONCAT(distinct cs_code order by cs_id separator ', ') 'ContentStandards',
GROUP_CONCAT(distinct c_name order by c_id separator ', ') 'Categories',
GROUP_CONCAT(distinct s_name order by s_id separator ', ') 'SchoolSubjects'
FROM (
SELECT r.res_id, r.res_status, r.res_type, r.res_category, r.res_title, r.res_filename, r.res_source, r.res_gradelevel_from, r.res_gradelevel_to, r.res_tags, r.res_description, r.res_onserver, r.res_favoriteaccts, r.res_CreatedOn, c_id, s_id, t_id, ch_id, cs_id,
CONCAT("<a class=""ReportLink"" href=""page.asp?category=",c_name,""" title=""",c_name,""">",c_name,"</a>") as c_name,
CONCAT("<a class=""ReportLink"" href=""page.asp?subject=",s_name,""" title=""",s_name,""">",s_name,"</a>") as s_name,
CONCAT("<a class=""ReportLink"" href=""page.asp?topic=",t_name,""" title=""",t_name,""">",t_name,"</a>") as t_name,
CONCAT("<a class=""ReportLink"" href=""page.asp?cs=",cs_code,""" title=""",cs_code,""">",cs_code,"</a>") as cs_code,
CONCAT("<a class=""ReportLink"" href=""page.asp?chapter=",ch_title,""" title=""",ch_title,""">",ch_code,": ",ch_title,"</a>") as ch_title
FROM hre_resources r
LEFT JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id
LEFT JOIN topics t on t.t_id = ttr.rt_topicid
LEFT JOIN topic_to_cs tcs on tcs.cst_topicid = t.t_id
LEFT JOIN categories c ON c_id = r.res_category
LEFT JOIN topic_to_framework ttc on ttc.ft_topicid = t.t_id
LEFT JOIN ca_hss_frameworkchapters ch ON ch.ch_id = ttc.ft_frameworkid
LEFT JOIN ca_hss_contentstandards cs ON cs.cs_id = tcs.cst_contentstandardid
LEFT JOIN schoolsubjects_to_resource str ON str.sr_resid = r.res_id
LEFT JOIN schoolsubjects s ON s.s_id = str.sr_sid) links
WHERE RES_Status = 'Active'
GROUP BY RES_ID
ORDER BY RES_Title ASC, RES_Source DESC
該查詢從我們的mySQL DB返回64個完全格式化的記錄，但是要花100秒鍾以上的時間。
查詢分析器將主要違規者顯示為：
+-------------------------------+-----------+
| Sending data | 34.530026 |
+-------------------------------+-----------+
| Creating sort index | 24.205878 |
| Storing result in query cache | 56.739204 |
+-------------------------------+-----------+
解釋結果如下：
+----+-------------+------------+--------+---------------+---------------+---------+------------------------------------+------+---------------------------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+------------+--------+---------------+---------------+---------+------------------------------------+------+---------------------------------------------------------------------+
| 1 | PRIMARY | <derived2> | ref | <auto_key0> | <auto_key0> | 77 | const | 10 | Using index condition; Using where; Using temporary; Using filesort |
| 2 | DERIVED | r | ALL | NULL | NULL | NULL | NULL | 64 | NULL |
| 2 | DERIVED | ttr | ref | RT_ResourceID | RT_ResourceID | 4 | uhri_hre.r.RES_ID | 3 | Using where |
| 2 | DERIVED | t | eq_ref | PRIMARY | PRIMARY | 4 | uhri_hre.ttr.RT_TopicID | 1 | Using where |
| 2 | DERIVED | tcs | ref | CST_TopicID | CST_TopicID | 4 | uhri_hre.t.T_ID | 9 | Using where |
| 2 | DERIVED | c | eq_ref | PRIMARY | PRIMARY | 4 | uhri_hre.r.RES_Category | 1 | Using where |
| 2 | DERIVED | ttc | ref | FT_TopicID | FT_TopicID | 4 | uhri_hre.t.T_ID | 21 | Using where |
| 2 | DERIVED | ch | eq_ref | PRIMARY | PRIMARY | 4 | uhri_hre.ttc.FT_FrameworkID | 1 | Using where |
| 2 | DERIVED | cs | eq_ref | PRIMARY | PRIMARY | 4 | uhri_hre.tcs.CST_ContentStandardID | 1 | Using where |
| 2 | DERIVED | str | ref | SR_RESID | SR_RESID | 4 | uhri_hre.r.RES_ID | 1 | Using where |
| 2 | DERIVED | s | eq_ref | PRIMARY | PRIMARY | 4 | uhri_hre.str.SR_SID | 1 | Using where |
+----+-------------+------------+--------+---------------+---------------+---------+------------------------------------+------+---------------------------------------------------------------------+
這些表具有以下索引。 未列出的表在ID字段（主鍵）上具有索引：
HRE_Resources:
+--------------+-------+--------+--------+--------------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+--------------+-------+--------+--------+--------------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | RES_ID | 64 | A | | |
| RES_Type | BTREE | No | No | RES_Type | 4 | A | | |
| RES_Category | BTREE | No | No | RES_Category | 10 | A | | |
| RES_Status | BTREE | No | No | RES_Status | 4 | A | | |
| RES_Language | BTREE | No | No | RES_Language | 8 | A | | |
| RES_Source | BTREE | No | No | RES_Source | 21 | A | | |
+--------------+-------+--------+--------+--------------+-------------+-----------+------+---------+
Topics:
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | T_ID | 39 | A | | |
| T_Name | BTREE | No | No | T_Name | 39 | A | | |
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
Topic_to_CS:
+-----------------------+-------+--------+--------+-----------------------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+-----------------------+-------+--------+--------+-----------------------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | CST_ID | 685 | A | | |
| CST_ContentStandardID | BTREE | No | No | CST_ContentStandardID | 228 | A | | |
| CST_TopicID | BTREE | No | No | CST_TopicID | 76 | A | | |
+-----------------------+-------+--------+--------+-----------------------+-------------+-----------+------+---------+
Topic_to_Framework:
+----------------+-------+--------+--------+----------------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+----------------+-------+--------+--------+----------------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | FT_ID | 471 | A | | |
| FT_TopicID | BTREE | No | No | FT_TopicID | 22 | A | | |
| FT_FrameworkID | BTREE | No | No | FT_FrameworkID | 235 | A | | |
+----------------+-------+--------+--------+----------------+-------------+-----------+------+---------+
Topic_to_Resource:
+---------------+-------+--------+--------+---------------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+---------------+-------+--------+--------+---------------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | RT_ID | 387 | A | | |
| RT_ResourceID | BTREE | No | No | RT_ResourceID | 129 | A | | |
| RT_TopicID | BTREE | No | No | RT_TopicID | 77 | A | | |
+---------------+-------+--------+--------+---------------+-------------+-----------+------+---------+
Schoolsubject_to_Resource:
+----------+-------+--------+--------+----------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+----------+-------+--------+--------+----------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | SR_ID | 228 | A | | |
| SR_SID | BTREE | No | No | SR_SID | 25 | A | | |
| SR_RESID | BTREE | No | No | SR_RESID | 228 | A | | |
+----------+-------+--------+--------+----------+-------------+-----------+------+---------+
Categories:
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
| Keyname | Type | Unique | Packed | Column | Cardinality | Collation | Null | Comment |
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
| PRIMARY | BTREE | Yes | No | C_ID | 9 | A | | |
| C_Name | BTREE | No | No | C_Name | 9 | A | | |
+---------+-------+--------+--------+--------+-------------+-----------+------+---------+
其中一些索引是使用在其他查詢中使用的更復雜的WHERE創建的。
我出於其他目的在數據庫上運行了復雜的查詢，這些查詢與上面的查詢無關，並且名義上執行得很好。 因此，我認為這不是服務器資源問題。
誰能在上面的查詢中看到任何可能導致響應緩慢的內容？
提前謝謝了！
PS。 根據以下請求從服務器添加一些信息...
+------------------------------+---------+
| Variable_name | Value |
+------------------------------+---------+
| query_alloc_block_size | 8192 |
| query_cache_limit | 1048576 |
| query_cache_min_res_unit | 4096 |
| query_cache_size | 1048576 |
| query_cache_type | ON |
| query_cache_wlock_invalidate | OFF |
| query_prealloc_size | 8192 |
+------------------------------+---------+
+-------------------------+--------+
| Variable_name | Value |
+-------------------------+--------+
| Qcache_free_blocks | 9 |
| Qcache_free_memory | 22736 |
| Qcache_hits | 121910 |
| Qcache_inserts | 9296 |
| Qcache_lowmem_prunes | 8213 |
| Qcache_not_cached | 29475 |
| Qcache_queries_in_cache | 103 |
| Qcache_total_blocks | 295 |
+-------------------------+--------+
正如我在上面的評論中提到的那樣，您似乎正在從多個表關系中獲取大量數據。 這將導致多個笛卡爾積 ，這就是為什么要獲得626K行的原因。
解決方案是將其分解為單個查詢。
這是我對您的模型的了解：
這是各個查詢及其各自的EXPLAIN計划的樣子。
您可以看到，這消除了所有子查詢和臨時表，消除了笛卡爾乘積，因此您無需在任何地方使用DISTINCT，並且所有聯接都很好地針對主鍵。 它可能看起來是重復的，但是查詢優化得更好的事實應該使其運行得更快。
EXPLAIN
SELECT r.res_id, r.res_status, r.res_type, r.res_category, r.res_title, r.res_filename,
r.res_source, r.res_gradelevel_from, r.res_gradelevel_to, r.res_tags, r.res_description,
r.res_onserver, r.res_favoriteaccts, r.res_CreatedOn, c.c_name AS 'Categories'
FROM hre_resources AS r
INNER JOIN categories c ON c_id = r.res_category
WHERE r.res_status = 'Active'
--------------
+----+-------------+-------+--------+-------------------------+------------+---------+---------------------+------+-----------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+-------------------------+------------+---------+---------------------+------+-----------------------+
| 1 | SIMPLE | r | ref | res_status,res_category | res_status | 1 | const | 1 | Using index condition |
| 1 | SIMPLE | c | eq_ref | PRIMARY | PRIMARY | 4 | test.r.res_category | 1 | NULL |
+----+-------------+-------+--------+-------------------------+------------+---------+---------------------+------+-----------------------+
EXPLAIN
SELECT r.res_id, GROUP_CONCAT(s.s_name ORDER BY s.s_id SEPARATOR ', ') AS 'SchoolSubjects'
FROM hre_resources AS r
INNER JOIN schoolsubjects_to_resource str ON str.sr_resid = r.res_id
INNER JOIN schoolsubjects s ON s.s_id = str.sr_sid
WHERE r.res_status = 'Active'
GROUP BY r.res_id
--------------
+----+-------------+-------+--------+---------------------------------+------------+---------+-----------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------+------------+---------+-----------------+------+--------------------------+
| 1 | SIMPLE | r | ref | PRIMARY,res_status,res_category | res_status | 1 | const | 1 | Using where; Using index |
| 1 | SIMPLE | str | ref | PRIMARY,sr_sid | PRIMARY | 4 | test.r.res_id | 1 | Using index |
| 1 | SIMPLE | s | eq_ref | PRIMARY | PRIMARY | 4 | test.str.sr_sid | 1 | NULL |
+----+-------------+-------+--------+---------------------------------+------------+---------+-----------------+------+--------------------------+
3 rows in set (0.00 sec)
--------------
EXPLAIN
SELECT r.res_id, GROUP_CONCAT(t.t_name ORDER BY t_id SEPARATOR ', ') AS 'Topics'
FROM hre_resources AS r
INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id
INNER JOIN topics t on t.t_id = ttr.rt_topicid
WHERE r.res_status = 'Active'
GROUP BY r.res_id
--------------
+----+-------------+-------+--------+---------------------------------+------------+---------+---------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------+------------+---------+---------------------+------+--------------------------+
| 1 | SIMPLE | r | ref | PRIMARY,res_status,res_category | res_status | 1 | const | 1 | Using where; Using index |
| 1 | SIMPLE | ttr | ref | PRIMARY,rt_topicid | PRIMARY | 4 | test.r.res_id | 1 | Using index |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY | 4 | test.ttr.rt_topicid | 1 | NULL |
+----+-------------+-------+--------+---------------------------------+------------+---------+---------------------+------+--------------------------+
3 rows in set (0.00 sec)
--------------
EXPLAIN
SELECT r.res_id, GROUP_CONCAT(DISTINCT CONCAT(ch.ch_code, ':', ch.ch_title) ORDER BY ch.ch_id SEPARATOR ', ') AS 'Chapters'
FROM hre_resources AS r
INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id
INNER JOIN topics t on t.t_id = ttr.rt_topicid
INNER JOIN topic_to_framework ttc on ttc.ft_topicid = t.t_id
INNER JOIN ca_hss_frameworkchapters ch ON ch.ch_id = ttc.ft_frameworkid
WHERE r.res_status = 'Active'
GROUP BY r.res_id
--------------
+----+-------------+-------+--------+---------------------------------+------------+---------+-------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------+------------+---------+-------------------------+------+--------------------------+
| 1 | SIMPLE | r | ref | PRIMARY,res_status,res_category | res_status | 1 | const | 1 | Using where; Using index |
| 1 | SIMPLE | ttr | ref | PRIMARY,rt_topicid | PRIMARY | 4 | test.r.res_id | 1 | Using index |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY | 4 | test.ttr.rt_topicid | 1 | Using index |
| 1 | SIMPLE | ttc | ref | PRIMARY,ft_frameworkid | PRIMARY | 4 | test.ttr.rt_topicid | 1 | Using index |
| 1 | SIMPLE | ch | eq_ref | PRIMARY | PRIMARY | 4 | test.ttc.ft_frameworkid | 1 | NULL |
+----+-------------+-------+--------+---------------------------------+------------+---------+-------------------------+------+--------------------------+
5 rows in set (0.00 sec)
--------------
EXPLAIN
SELECT r.res_id, GROUP_CONCAT(DISTINCT cs.cs_code ORDER BY cs.cs_id SEPARATOR ', ') AS 'ContentStandards'
FROM hre_resources AS r
INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id
INNER JOIN topics t on t.t_id = ttr.rt_topicid
INNER JOIN topic_to_cs tcs on tcs.cst_topicid = t.t_id
INNER JOIN ca_hss_contentstandards cs ON cs.cs_id = tcs.cst_contentstandardid
WHERE r.res_status = 'Active'
GROUP BY r.res_id
--------------
+----+-------------+-------+--------+---------------------------------+------------+---------+--------------------------------+------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+--------+---------------------------------+------------+---------+--------------------------------+------+--------------------------+
| 1 | SIMPLE | r | ref | PRIMARY,res_status,res_category | res_status | 1 | const | 1 | Using where; Using index |
| 1 | SIMPLE | ttr | ref | PRIMARY,rt_topicid | PRIMARY | 4 | test.r.res_id | 1 | Using index |
| 1 | SIMPLE | t | eq_ref | PRIMARY | PRIMARY | 4 | test.ttr.rt_topicid | 1 | Using index |
| 1 | SIMPLE | tcs | ref | PRIMARY,cst_contentstandardid | PRIMARY | 4 | test.ttr.rt_topicid | 1 | Using index |
| 1 | SIMPLE | cs | eq_ref | PRIMARY | PRIMARY | 4 | test.tcs.cst_contentstandardid | 1 | NULL |
+----+-------------+-------+--------+---------------------------------+------------+---------+--------------------------------+------+--------------------------+
以下是我為這些表假定的DDL。 如果您將其包含在原始問題中，將會很有幫助。
CREATE TABLE categories (
c_id INT PRIMARY KEY,
c_name VARCHAR(100) NOT NULL DEFAULT 'c_name'
);
CREATE TABLE hre_resources (
res_id INT PRIMARY KEY,
res_category INT NOT NULL,
res_status ENUM('Active', 'Inactive') NOT NULL DEFAULT 'Active',
res_type VARCHAR(100) NOT NULL DEFAULT 'type',
res_title VARCHAR(100) NOT NULL DEFAULT 'title',
res_filename VARCHAR(100) NOT NULL DEFAULT '',
res_source VARCHAR(100) NOT NULL DEFAULT '',
res_gradelevel_from VARCHAR(100) NOT NULL DEFAULT '',
res_gradelevel_to VARCHAR(100) NOT NULL DEFAULT '',
res_tags VARCHAR(100) NOT NULL DEFAULT '',
res_description VARCHAR(100) NOT NULL DEFAULT '',
res_onserver VARCHAR(100) NOT NULL DEFAULT '',
res_favoriteaccts VARCHAR(100) NOT NULL DEFAULT '',
res_CreatedOn DATE NOT NULL DEFAULT '2017-01-01',
KEY (res_status),
FOREIGN KEY (res_category) REFERENCES categories(c_id)
);
CREATE TABLE topics (
t_id INT PRIMARY KEY,
t_name VARCHAR(100) NOT NULL DEFAULT 't_name'
);
CREATE TABLE ca_hss_frameworkchapters (
ch_id INT PRIMARY KEY,
ch_title VARCHAR(100) NOT NULL DEFAULT 'ch_title',
ch_code VARCHAR(100) NOT NULL DEFAULT 'ch_code'
);
CREATE TABLE ca_hss_contentstandards (
cs_id INT PRIMARY KEY,
cs_code VARCHAR(100) NOT NULL DEFAULT 'cs_code'
);
CREATE TABLE schoolsubjects (
s_id INT PRIMARY KEY,
s_name VARCHAR(100) NOT NULL DEFAULT 's_name'
);
CREATE TABLE topic_to_framework (
ft_topicid INT NOT NULL,
ft_frameworkid INT NOT NULL,
PRIMARY KEY (ft_topicid, ft_frameworkid),
FOREIGN KEY (ft_topicid) REFERENCES topics(t_id),
FOREIGN KEY (ft_frameworkid) REFERENCES ca_hss_frameworkchapters(ch_id)
);
CREATE TABLE topic_to_resource (
rt_resourceid INT NOT NULL,
rt_topicid INT NOT NULL,
PRIMARY KEY (rt_resourceid, rt_topicid),
FOREIGN KEY (rt_resourceid) REFERENCES hre_resources (res_id),
FOREIGN KEY (rt_topicid) REFERENCES topics(t_id)
);
CREATE TABLE topic_to_cs (
cst_topicid INT NOT NULL,
cst_contentstandardid INT NOT NULL,
PRIMARY KEY (cst_topicid, cst_contentstandardid),
FOREIGN KEY (cst_topicid) REFERENCES topics(t_id),
FOREIGN KEY (cst_contentstandardid) REFERENCES ca_hss_contentstandards(cs_id)
);
CREATE TABLE schoolsubjects_to_resource (
sr_resid INT NOT NULL,
sr_sid INT NOT NULL,
PRIMARY KEY (sr_resid, sr_sid),
FOREIGN KEY (sr_resid) REFERENCES hre_resources(res_id),
FOREIGN KEY (sr_sid) REFERENCES schoolsubjects(s_id)
);
這是Python中通過將多個查詢的結果合並在一起的示例。
import pprint
import MySQLdb
import MySQLdb.cursors
db = MySQLdb.connect(host="localhost", db="test", cursorclass=MySQLdb.cursors.DictCursor)
cur = db.cursor()
res_data = {}
sql = """SELECT r.res_id, r.res_status, r.res_type, r.res_category, r.res_title, r.res_filename, r.res_source, r.res_gradelevel_from, r.res_gradelevel_to, r.res_tags, r.res_description, r.res_onserver, r.res_favoriteaccts, r.res_CreatedOn, c.c_name AS 'Categories' FROM hre_resources AS r INNER JOIN categories c ON c_id = r.res_category WHERE r.res_status = 'Active'"""
cur.execute(sql)
for row in cur.fetchall():
res_data[row['res_id']] = row
sql = """SELECT r.res_id, GROUP_CONCAT(s.s_name ORDER BY s.s_id SEPARATOR ', ') AS 'SchoolSubjects' FROM hre_resources AS r INNER JOIN schoolsubjects_to_resource str ON str.sr_resid = r.res_id INNER JOIN schoolsubjects s ON s.s_id = str.sr_sid WHERE r.res_status = 'Active' GROUP BY r.res_id"""
cur.execute(sql)
for row in cur.fetchall():
res_data[row['res_id']].update(row)
sql = """SELECT r.res_id, GROUP_CONCAT(t.t_name ORDER BY t_id SEPARATOR ', ') AS 'Topics' FROM hre_resources AS r INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id INNER JOIN topics t on t.t_id = ttr.rt_topicid WHERE r.res_status = 'Active' GROUP BY r.res_id"""
cur.execute(sql)
for row in cur.fetchall():
res_data[row['res_id']].update(row)
sql = """SELECT r.res_id, GROUP_CONCAT(DISTINCT CONCAT(ch.ch_code, ':', ch.ch_title) ORDER BY ch.ch_id SEPARATOR ', ') AS 'Chapters' FROM hre_resources AS r INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id INNER JOIN topics t on t.t_id = ttr.rt_topicid INNER JOIN topic_to_framework ttc on ttc.ft_topicid = t.t_id INNER JOIN ca_hss_frameworkchapters ch ON ch.ch_id = ttc.ft_frameworkid WHERE r.res_status = 'Active' GROUP BY r.res_id"""
cur.execute(sql)
for row in cur.fetchall():
res_data[row['res_id']].update(row)
sql = """SELECT r.res_id, GROUP_CONCAT(DISTINCT cs.cs_code ORDER BY cs.cs_id SEPARATOR ', ') AS 'ContentStandards' FROM hre_resources AS r INNER JOIN topic_to_resource ttr ON ttr.rt_resourceid = r.res_id INNER JOIN topics t on t.t_id = ttr.rt_topicid INNER JOIN topic_to_cs tcs on tcs.cst_topicid = t.t_id INNER JOIN ca_hss_contentstandards cs ON cs.cs_id = tcs.cst_contentstandardid WHERE r.res_status = 'Active' GROUP BY r.res_id"""
cur.execute(sql)
for row in cur.fetchall():
res_data[row['res_id']].update(row)
db.close()
pp = pprint.PrettyPrinter()
pp.pprint(res_data)
在向每個表添加一行偽數據后，我從上面的腳本中獲得了以下輸出：
{2L: {'Categories': 'c_name',
'Chapters': 'ch_codech_title',
'ContentStandards': 'cs_code',
'SchoolSubjects': 's_name',
'Topics': 't_name',
'res_CreatedOn': datetime.date(2017, 1, 1),
'res_category': 1L,
'res_description': '',
'res_favoriteaccts': '',
'res_filename': '',
'res_gradelevel_from': '',
'res_gradelevel_to': '',
'res_id': 2L,
'res_onserver': '',
'res_source': '',
'res_status': 'Active',
'res_tags': '',
'res_title': 'title',
'res_type': 'type'}}
首先將WHERE RES_Status = 'Active'派生表中。 這可能會顯着減小tmp表的大小，並可能顯着縮小“創建排序索引”階段。
然后專注於派生表。 分開。 多久時間？
至於56.7s部分，聽起來有些設置太高了。 請提供：
SHOW VARIABLES LIKE 'query%';
SHOW GLOBAL STATUS LIKE 'Qc%';
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