整体来说生成临时表内存空间,落磁盘临时表,临时表使用太 体现在 多表join,buffer_size设置不合理,alter algrithem copy等方式 Sorting result: For a SELECT statement, this is similar to Creating sort index, but for nontemporary tables. 结果集使用大的排序,基本上SQL语句上order by 字段上没有索引 上述...
6. Creating sort index 时间过长 这通常是因为在大量数据的表中进行 order by 操作导致的,在这样的情况下,order by 操作的性能可能会低到令人无法想象。 7. Copying to tmp table on disk 时间过长 这个状态是由于临时结果集大于 tmp_table_size,正在将临时表从内存存储转为磁盘存储,这是一个非常耗时的操作...
A SQL non-equijoin (also known as a θ-join) effects a relation between two tables based on a filteredCROSS JOINbetween two tables. This type of join can be a range comparison using theBETWEENoperator or a comparison of column values that uses an inequality operator. A SQL antijoin may ...
No duplicates exist but get Msg 2627, Cannot insert duplicate key in object No logging in sql server No way to: SELECT * FROM MY_TABLE ORDER BY PRIMARY KEY?? NOLOCK and COUNT(*) NOLOCK or WITH(NOLOCK) SQL SEVER 2012 Non Ansi style Left Outer Join non breaking space characters Non-U...
The merge join operation is either a regular or a many-to-many operation. A many-to-many merge join uses a temporary table to store rows. If there are duplicate values from each input, one of the inputs has to rewind to the start of the duplicates as each duplicate from the other in...
Remove the OUTER JOIN operator or do not place table function in a nested explicit join. Remove the function from the default clause for the global variable or parameter of a procedure definition. For reason codes 1, 2, and 3, the query can be rewritten using a common table expression to...
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重复的记录。因此,MySQL需要再次去掉重复的记录,然后再把结果发送给客户端。 Reopen table 获得了对一个表的锁,但是必须在表结构修改之后才能获得这个锁。已经释放锁,关闭数据表,正尝试重新打开数据表。
When creating statistics with the CREATE STATISTICS statement, we recommend keeping the AUTO_CREATE_STATISTICS option ON so that the Query Optimizer continues to routinely create single-column statistics for query predicate columns. For more information about query predicates, see Search condition. Conside...
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...
Getting your Database ready - covers the basic of creating a database, inserting data, and writing a query Constraints - a rule that you apply or abide by while doing SQL operations. This chapter examines selective fields INSERT, primary key constraint, unique key constraint, and the difference...