how to optimize sql query using execution plan

* from T_userinfo where userid= ' Abcde12ef ' Note: If the lookup condition behind the where has a clustered index column. That is, when and only if the condition behind the where contains a clustered index. 4. Index Scan:The overall scan of nonclustered indexes. To create a nonclustered index: CREATE nonclustered INDEX ix_name on T_userinfo (UserName) Select UserName from T_userinfo---as long as not all columns * Note: When you do not overwrite and include all of the required columns in

Explain select * from film where rating>9\g; Select_type Represents the type of select Simple Represents a simple table without table joins or subqueries Primry Main query (outer query) UNION The second or subsequent query sta

MySQL5.6 how to optimize slow query SQL statements -- Introduction to slow logs Recently, a development team complained that the mysql cluster included in our platform was not good and always reported the "heartbeat Error" of mysql and analyzed the logs they collected, no network problems were found between mysql cluster nodes, but a very interesting phenomenon w

Label:If encountering a binding snooping causes a slow execution schedule, want to clear a SQL execution plan, let it hard parse, for a long time did not find a direct operation share pool method (unless alter system flush Shared_pool), SQL can only be hardened by parsing th

Let's take a look at what bookmarks are:When the non-clustered index selected by the optimizer only contains a part of the query request fields, a lookup is required to retrieve other fields to meet the request. For a table with clustered indexes, it is a key lookup, and for a heap table it is an RID lookup ). This kind of search is-bookmarks search.Bookmarksearch reads data from the table based on the index row locator. Therefore, in addition to the

Let's take a look at what bookmarks are: When the non-clustered index selected by the optimizer only contains a part of the query request fields, a lookup is required to retrieve other fields to meet the request. For a table with clustered indexes, it is a key lookup, and for a heap table it is an RID lookup ). This kind of search is-bookmarks search. Bookmarksearch reads data from the table based on the index row locator. Therefore, in addition to t

Before executing an SQL statement, Oracle needs to first check the SQL Execution Plan and then execute the SQL statement according to the execution plan. The optimizer is responsible fo

months. Read the online Help documentation for SQL Server, which describes the restrictions on the size of the job history log-> The job system, the right-click Property,->sql Server Agent, and the maximum size of the job history log (rows) Default is 1000 if a machine has a large number of jobs, be sure to increase it, for example, 100000 the maximum number of rows per job history log defaults to 100 if

at the SQL Run schedule: ID Select_type Table type Possible_keys Key Key_len ref rows Extra 1 Simple T Range PRIMARY PRIMARY 24 299392 Using index condition; Using Filesort 1 Simple R Eq_ref PRIMARY

you find slow statements and provide optimization solutions. In MySQL, you need to enable slow log records for analysis (records can be saved in tables or files. by default, they are saved in files, and our system uses the default method ). First, let's take a look at what the records in the MySQL slow query log look like: Time Id Command Argument# Time: 141010 9:33:57# User@Host: root[root] @ localhost [] Id: 1# Query_time:

: It can be seen that there is a clustered index PK_UserID and a non-clustered index IX_UserName. Look at the effect of creating a bookmarked search: Select UserName, Gender from dbo. UserInfo where UserName = 'usern600' According to the preceding SQL Execution Plan, a Key Lookup is generated, as shown in figure If you rewrite the preceding

Tag:oraclesql optimization Execution Plan gg HP UNIX monitors a process that consumes high CPU and later finds that there is a problem with the statement execution plan in GG, which causes the CPU to be high. Since the statements in GG cannot be changed, how can you change the ex