為什么選擇不同的列會影響mysql 5.6中的查詢速度？

Question

我在mysql5.6中有一個表cdc_bond_valuation：

+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+
| table_schema | table_name         | index_schema | index_name                      | seq_in_index | column_name  | cardinality |
+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+
| ss_product   | cdc_bond_valuation | ss_product   | IDX_cdc_bond_valuation_Bond_Key |            1 | Bond_Key     |      377844 |
| ss_product   | cdc_bond_valuation | ss_product   | IndexValuateDate                |            1 | Valuate_Date |      143025 |
| ss_product   | cdc_bond_valuation | ss_product   | PRIMARY                         |            1 | ID           |    25315548 |
+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+



query 1:
SELECT  Valuate_Date  FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;

query 2:
SELECT ID, Valuate_Date  FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;

query 3:
SELECT  Bond_Key FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;

query 4:
SELECT  Bond_Key,Valuate_Date FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;


explain 1:
mysql> explain SELECT  Valuate_Date  FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
| id | select_type | table              | type | possible_keys    | key              | key_len | ref   | rows  | Extra       |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
|  1 | SIMPLE      | cdc_bond_valuation | ref  | IndexValuateDate | IndexValuateDate | 5       | const | 98156 | Using index |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
1 row in set

explain 2:
mysql> explain SELECT  ID,Valuate_Date FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
| id | select_type | table              | type | possible_keys    | key              | key_len | ref   | rows  | Extra       |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
|  1 | SIMPLE      | cdc_bond_valuation | ref  | IndexValuateDate | IndexValuateDate | 5       | const | 98156 | Using index |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------------+
1 row in set


explain 3:
mysql> explain SELECT  Bond_Key FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
| id | select_type | table              | type | possible_keys    | key              | key_len | ref   | rows  | Extra |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
|  1 | SIMPLE      | cdc_bond_valuation | ref  | IndexValuateDate | IndexValuateDate | 5       | const | 98156 | NULL  |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
1 row in set

explain 4:
mysql> explain SELECT  Bond_Key,Valuate_Date FROM cdc_bond_valuation WHERE Valuate_Date = 20181203;
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
| id | select_type | table              | type | possible_keys    | key              | key_len | ref   | rows  | Extra |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
|  1 | SIMPLE      | cdc_bond_valuation | ref  | IndexValuateDate | IndexValuateDate | 5       | const | 98156 | NULL  |
+----+-------------+--------------------+------+------------------+------------------+---------+-------+-------+-------+
1 row in set



mysql> select table_schema,
       table_name,
       index_schema,
       index_name,
       seq_in_index,
       column_name,
       cardinality
  from information_schema.statistics
 where table_name = 'cdc_bond_valuation'
 order by table_schema, table_name, index_name, seq_in_index;

+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+
| table_schema | table_name         | index_schema | index_name                      | seq_in_index | column_name  | cardinality |
+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+
| ss_product   | cdc_bond_valuation | ss_product   | IDX_cdc_bond_valuation_Bond_Key |            1 | Bond_Key     |      377844 |
| ss_product   | cdc_bond_valuation | ss_product   | IndexValuateDate                |            1 | Valuate_Date |      143025 |
| ss_product   | cdc_bond_valuation | ss_product   | PRIMARY                         |            1 | ID           |    25315548 |
+--------------+--------------------+--------------+---------------------------------+--------------+--------------+-------------+
3 rows in set

mysql> 

上面的表中有4個查詢，它們都使用索引IndexValuateDate，但是查詢1和2非常快（不到1秒），但是查詢3和4非常慢（超過1000秒）。

我注意到1和2僅使用索引來反饋查詢（ID是主鍵，而Valuate_Date已索引）。 3和4首先使用Valuate_Date上的索引過濾表，然后返回表以獲取具有rowid的列？ 為什么不僅僅使用像1和2這樣的索引，因為Bond_Key也被索引了？

Answer 1

請提供SHOW CREATE TABLE 。

InnoDB默默地將PRIMARY KEY的列添加到每個輔助鍵。 因此，查詢1和2執行相同。 他們只使用索引。 這在EXPLAIN通過Using index 。 也就是說， INDEX(Valuate_Date)包含所需的列，而其他列則不需要。

EXPLAINs指示使用了相同的索引，但是沒有“覆蓋”（沒有提到Using index ）。 因此，指數呈線性掃描，但對於每一個估計的98156項與日期，它不得不尋找（在數據的B樹）的價值Bond_Key 。 這種額外的查找導致嚴重的速度下降。 （這1000秒與在HDD上執行98156磁盤命中匹配得很好。）

為了快速進行所有4個查詢， IndexValuateDate用此復合索引替換IndexValuateDate ，並按給定的順序排列列：

INDEX(Valuate_Date, Bond_Key, ID)

我可以建議您通過DATE數據類型而不是DECIMAL(8,0) 。

與其他數據庫不同，MySQL沒有“ rowid”。 而是在BTree中使用PRIMARY KEY對數據進行排序。

Answer 2

    CREATE TABLE `cdc_bond_valuation` (
  `ID` varchar(32) NOT NULL,
  `Bond_Key` varchar(25) DEFAULT NULL,
  `Short_Name` varchar(32) DEFAULT NULL,
  `Bond_ID` varchar(32) DEFAULT NULL,
  `Valuate_Date` decimal(8,0) DEFAULT NULL,
  `Listed_Market` varchar(3) DEFAULT NULL,
  `Remaining_Year` decimal(7,4) DEFAULT NULL,
  `Val_Intraday_Dirty_Price` decimal(7,4) DEFAULT NULL,
  `Val_Intraday_Accrued_Interest` decimal(7,4) DEFAULT NULL,
  `Val_Clean_Price` decimal(7,4) DEFAULT NULL,
  `Val_Yield` decimal(7,4) DEFAULT NULL,
  `Val_Modified_Duration` decimal(7,4) DEFAULT NULL,
  `Val_Convexity` decimal(7,4) DEFAULT NULL,
  `Val_Basis_Point_Value` decimal(7,4) DEFAULT NULL,
  `Val_Spread_Duration` decimal(7,4) DEFAULT NULL,
  `Val_Spread_Convexity` decimal(7,4) DEFAULT NULL,
  `Market_Dirty_Price` decimal(7,4) DEFAULT NULL,
  `Market_Clean_Price` decimal(7,4) DEFAULT NULL,
  `Market_Yield` decimal(7,4) DEFAULT NULL,
  `Market_Modified_Duration` decimal(7,4) DEFAULT NULL,
  `Market_Convexity` decimal(7,4) DEFAULT NULL,
  `Market_Basis_Point_Value` decimal(7,4) DEFAULT NULL,
  `Market_Spread_Duration` decimal(7,4) DEFAULT NULL,
  `Market_Spread_Convexity` decimal(7,4) DEFAULT NULL,
  `Credibility` varchar(16) DEFAULT NULL,
  `Val_Rate_Duration` decimal(7,4) DEFAULT NULL,
  `Val_Rate_Convexity` decimal(7,4) DEFAULT NULL,
  `Market_Rate_Duration` decimal(7,4) DEFAULT NULL,
  `Market_Rate_Convexity` decimal(7,4) DEFAULT NULL,
  `Val_Closed_Dirty_Price` decimal(7,4) DEFAULT NULL,
  `Val_Closed_Accrued_Interest` decimal(7,4) DEFAULT NULL,
  `Remaining_Par_Value` decimal(7,4) DEFAULT NULL,
  `Val_Spread` decimal(7,4) DEFAULT NULL,
  `Yield_Curve_ID` varchar(128) DEFAULT NULL,
  `Market_Spread` decimal(7,4) DEFAULT NULL,
  `Absolute_Liquidity_Coefficient` decimal(7,4) DEFAULT NULL,
  `Position_Percentage` decimal(7,4) DEFAULT NULL,
  `Relative_Liquidity_Coefficient` decimal(7,4) DEFAULT NULL,
  `Relative_Liquidity_Value` decimal(7,4) DEFAULT NULL,
  `Option` varchar(8) DEFAULT NULL ,
  PRIMARY KEY (`ID`),
  KEY `IndexValuateDate` (`Valuate_Date`) USING BTREE,
  KEY `ValuateDateBondKey` (`Valuate_Date`,`Bond_Key`),
  KEY `IndexBondKey` (`Bond_Key`,`Listed_Market`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8

Answer 3

查詢5：

mysql> explain SELECT Bond_Key, Valuate_Date  FROM cdc_bond_valuation WHERE Valuate_Date = 20181203  and bond_key='C0000832017CORLEB01';
+----+-------------+--------------------+------+--------------------------------------------------+---------------------------------+---------+-------+------+------------------------------------+
| id | select_type | table              | type | possible_keys                                    | key                             | key_len | ref   | rows | Extra                              |
+----+-------------+--------------------+------+--------------------------------------------------+---------------------------------+---------+-------+------+------------------------------------+
|  1 | SIMPLE      | cdc_bond_valuation | ref  | IndexValuateDate,IDX_cdc_bond_valuation_Bond_Key | IDX_cdc_bond_valuation_Bond_Key | 78      | const |  787 | Using index condition; Using where |
+----+-------------+--------------------+------+--------------------------------------------------+---------------------------------+---------+-------+------+------------------------------------+
1 row in set

mysql> 

查詢5使用index（bond_key）進行過濾，然后像全表scann一樣掃描結果（787行）以查找bond_key。 查詢5根本不使用index（ValuateDate）。 那正確嗎？

Answer 4

SELECT  count(*)  FROM cdc_bond_valuation WHERE   bond_key='C0000832017CORLEB01';
SELECT  count(*)  FROM cdc_bond_valuation WHERE   bond_key='C0000832017CORLEB01' and Valuate_Date = 20181203;


+----------+
| count(*) |
+----------+
|      788 |
+----------+
1 row in set

+----------+
| count(*) |
+----------+
|        2 |
+----------+
1 row in set

mysql>