A. Optimization
Table 1. Data related query optimization
1. The first implementation where filtered and joint investigation;
2 suitable combination index,
3. field values:
1) make use of a digital type
2) setting default values, to avoid the use of field where null =;
4. certain keywords caution / character (! in, =, *) , the appropriate use exists / not exists;
2.limit optimization
Normal:
the SELECT * `key` the FROM table1 the WHERE> 1000000 the LIMIT 100000,5;
inline: a table inline - temporary table (a table using the result set derived limit)
the SELECT * a the FROM table1
the INNER the JOIN (the SELECT` key` AS id FROM table1 WHERE `key`> 1000000 LIMIT 100000,5) b ON a.`key` = b .id;
3. Sort optimization:
1) to make use of the positive sequence index ordering, without using a separate order by
2) When using the index order: combination index - index and field index sort fields in combination where
II. Query result set sorting number
SELECT @rank: = @ rank + 1 AS rank_no // @ rank temporary variables, @rank: = @ rank + 1 the initial value + 1'd
FROM
(the SELECT Field FROM table ORDER BY `key` DESC) a, // results set sorting
(SELECT @rank: = 0) b // temporary variable initial value
III. Other
1. The initial value of a specified increment primary key
alter table tbname auto_increment = x;
2.lpad ((str, just padstr))
Padstr of string str, fill the left until it reaches the length len characters in length, then return str, len If the length is longer than str, it will be amputated to len characters;
3. Given a date, returns a few days
TO_DAYS(date)
4. Analyzing whether the value of a field containing a specified character string
INSTR (filed, String)
5.replace into: This line has a data replacement (primary key or unique index determination)
Need to modify the data source configuration after 6.java project mysql jar 6.0 upgrade package
1.<property name="driverClassName" value="com.mysql.cj.jdbc.Driver"></property>
2.url 多加时区配置 serverTimezone=GMT%2B8
