mysql> alter table invoices add unique index (invoice_number); ERROR 1062 (23000): Duplicate entry '2' for key 1 mysql> alter ignore table invoices add unique index (invoice_number); Query OK, 4 rows affected (0.03 sec) Records: 4 Duplicates: 1 Warnings: 0 mysql> select * from invoice...
Sorting for order #正在为 ORDER BY 做排序。 Opening tables #这个过程应该会很快,除非受到其他因素的干扰。例如,在执 ALTER TABLE 或 LOCK TABLE 语句行完以前,数据表无法被其他线程打开。 正尝试打开一个表。 Removing duplicates #正在执行一个 SELECT DISTINCT 方式的查询,但是MySQL无法在前一个阶段优化掉那些...
查看某个 query 的耗时情况 通过上面的 SQL 就可以查询出指定 SQL 的耗时了。 3. SQL 状态一览 SQL 状态一览 4. closing tables 时间过长 closing tables 通常是因为磁盘 IO 能力不足引起的,可以排查磁盘 IO 的占用。 CPU load 高占用率低问题的排查 5. sending data 时间过长 5.1. 索引问题 最可能的原因...
这可能是困然很多人的一个问题,MySQL通过慢查询日志定位那些执行效率较低的SQL 语句,用--log-slow-queries[=file_name]选项启动时,mysqld 会写一个包含所有执行时间超过long_query_time 秒的SQL语句的日志文件,通过查看这个日志文件定位效率较低的SQL 。下面介绍MySQL中如何查询慢的SQL语句 一、MySQL数据库有几个...
mysql> insert into employees -> (name, hire_date, birth_date, email, phone_number, dept_id) -> ( -> select name, hire_date, birth_date, email, phone_number, dept_id -> from employees -> where name='张三' -> ); Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: ...
- For the union operator, use the first input to build the hash table (removing duplicates). Use the second input (which must have no duplicates) to probe the hash table, returning all rows that have no matches, then scan the hash table and return all entries.Hash ...
# ipad表的query字段的字符集是utf8,排序规则是utf8_general_ci, # 因此这两个表用query字段进行关联来查询的时候,索引会失效。 root@10.10.10.10(apple) > show create table iphone\G *** 1. row *** Table: iphone Create Table: CREATE TABLE `iphone` ( `id` bigint(5) ...
If multiple indexes are used in a single hint list, the duplicates are ignored, and the rest of the listed indexes are used to retrieve the rows of the table. The order of the indexes in the index hint is significant. A multiple index hint also enforces index ANDing, and the query opt...
Table names and aliases must not have duplicates in JOIN clauses. WHERE LIKE and NOT LIKE require a string literal. The following query results in error: MongoDB DocumentDB GROUP BY JetBrains Rider supports the GROUP BY clause. The SELECT clause may include expressions that functionally...
If multiple indexes are used in a single hint list, the duplicates are ignored, and the rest of the listed indexes are used to retrieve the rows of the table. The order of the indexes in the index hint is significant. A multiple index hint also enforces index ANDing, and the query opt...