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table, Empno and ename both create indexed columns, and when you need to perform an OR operation query between Empno and ename, consider changing these two queries to Union to improve performance.Select Empno,ename,job,sal from emp where empno > 7500 OR ename like ' s% ';Using UnionSelect Empno,ename,job,sal from emp where empno > 7500 unionselect empno,ename,job,sal from emp where ename like ' s% ';But this way, make sure that two columns are index columns. Otherwise, the or statement is not a

not in also to use caution, otherwise it will cause a full table scan, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t where num between 1 and 37, if the use of parameters in the WHERE clause, also causes a full table scan. Because SQL resolves local variables only at run time, the optimizer cannot defer the selection of access plans to run time; it must be selected at compile time. Howe

from t where num=10 or num=20You can query this:Select ID from t where num=10UNION ALLSelect ID from t where num=205.in and not in should also be used with caution, otherwise it will result in full table scans, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t where num between 1 and 36. The following query will also cause a full table scan:Select ID from t where name like '%abc% 'To be mo

, consider full-text indexing. 6, in and not in also to use caution, otherwise it will cause a full table scan, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t where num between 1 and 3 7, if the use of parameters in the WHERE clause, also causes a full table scan. Because SQL resolves local variables only at run time, the optimizer cannot defer the selection of access plans to run time;

againStart Service mysqld start (as mentioned in the previous step, some students may be service Mysql.server start) after logging inFor convenience, create a link file in the bin directory Ln-s/usr/local/mysql/bin/mysql/bin/mysql, of course, you can also add the path to the environment variables, such as: path= $PATH:/usr/local/mysql/ BinThis error is always reported after logging in:ERROR 2002 (HY000): Can ' t connect to local MySQL server through

operations3, in sub-query, try to use exists instead of inSelect from where inch (Select from userinfo b) can be changed to Select from where exists (Select1fromwhere= a.id)The following queries are much faster than in queries.4. In the WHERE clause try not to use is null or is not NULL to judge the fieldFor example:Select from where is NULLTry to avoid null in the database field, and if the condition is null for the query, the index will not be used, resulting in low query efficiency.There

Jpublisher utility to create a Java Stored Procedure with a PL/SQL wrapper that can is used to access the CO De. This approach are outline in the following note, available on MetaLink:Note 469588.1-dbws Callout Utilities User ' s Guide for RDBMS 11.1For more information in making Web service callouts from the database, see:Callout Users GuideUTL_DBWS Package ReferenceDeveloping a Web Service Client in the Database Join the Java Development MOS Community Forum for general

1. To optimize the query, avoid full-table scanning as far as possible, and first consider establishing an index on the columns involved in the Where and order by.2. Try to avoid using the! = or 3. Avoid null-valued fields in the WHERE clause, which will cause the engine to discard full-table scans using the index, such as:Select ID from t where num is nullYou can set the default value of 0 on NUM, make sure that the NUM column in the table does not have a null value, and then query:Select ID fr

not indexed, it will cause the engine to discard using the index for a full table scan, such as:Select ID from t where num=10 or Name = ' admin 'You can query this:Select ID from t where num = 10union allselect ID from t where Name = ' admin '5.in and not in should also be used with caution, otherwise it will result in full table scans, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t whe

, ',..., and set product's product_type_id to NOT NULL, and set its product_type_id to 0 when the product does not have a category, so the query can use the in The NER join. 3. Try to avoid using the! = or 4. You should try to avoid using or in the WHERE clause to join the condition, otherwise it may cause the engine to abandon the use of indexes for full table scanning, such as table T, Key1, Key2 on the index, need the following stored procedure:CREATE PROCEDURE Select_proc1 @key1 int=0, @ke

as:Select ID from t where num is nullThe ability to set the default value of 0 on NUM ensures that the NUM column in the table does not have a null value. Then this query:Select ID from t where num=0 3. You should try to avoid using the! = or 4. Try to avoid using or in the WHERE clause to join the condition, otherwise it will cause the engine to abandon using the index for full table scanSuch as:The select ID from t where num=10 or num=20 can be queried like this:Select ID from t where num=10

table scans, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t where num between 1 and 37. If you use a parameter in the WHERE clause, it also causes a full table scan. Because SQL resolves local variables only at run time, the optimizer cannot defer the selection of access plans to run time; it must be selected at compile time. However, if an access plan is established at compile time, th

), is occupied 100 characters of space, if it is varchar such a variable length field, NULL does not occupy space.You can set the default value of 0 on NUM, make sure that the NUM column in the table does not have a null value, and then query:Select ID from t where num = 03. Try to avoid using the! = or 4. Try to avoid using or in the WHERE clause to join the condition, if a field has an index and a field is not indexed, it will cause the engine to discard using the index for a full table scan,

created databaseMysql-uroot-pShow CREATE Database Water_station\g12.mysqldump-b parameter (no database exists when recovering)Mysqldump-uroot-p ' db123 '-B dbname >/opt/mysql_bak_b.sqlMysql-uroot-p ' db123 ' 13. File ComparisonDiff Mysql_bak.sql Mysql_bak_b.sql14. Optimize backup file size decrease input comment (debug debug)Mysqldump-uroot-p ' db123 '--compact-b dbname>/opt/mysql_bak_b_compact.sqlLess/opt/mysql_bak_b_compact.sql15. Specify the compression parameters to back up the database gzi

Tags: physical substr should be space speed judge temporary table will not be able to1. To optimize the query, avoid full-table scanning as far as possible, and first consider establishing an index on the columns involved in the Where and order by.2. Avoid null-valued fields in the WHERE clause, which will cause the engine to discard full-table scans using the index, such as:Select ID from t where num is nullYou can set the default value of 0 on NUM, make sure that the NUM column in the table do

, otherwise it will result in full table scans, such as: Select ID from t where num inFor consecutive values, you can use between instead of in: Select ID from t where num between 1 and 3 5. Fuzzy query The following query will also cause a full table scan: Select ID from t where name like '%abc% 'To be more efficient, consider full-text indexing. 6. If you use a parameter in the WHERE clause, it also causes a full table scan. Because SQL resolves loc

Tags: _for UNION All case Note exists first scenario closing sentence How to handle the millions database to improve processing query speedTo optimize the query, avoid full table scans, and first consider indexing on the columns involved in where and order by.2. Avoid null-valued fields in the WHERE clause, which will cause the engine to discard full-table scans using the index, such as:Select ID from t where num is nullYou can set the default value of 0 on NUM, make sure that the NUM column in

1. To optimize the query, avoid full-table scanning as far as possible, and first consider establishing an index on the columns involved in the Where and order by.2. Try to avoid using the! = or 3. Avoid null-valued fields in the WHERE clause, which will cause the engine to discard full-table scans using the index, such as:Select ID from t where num is nullYou can set the default value of 0 on NUM, make sure that the NUM column in the table does not have a null value, and then query:Select ID fr

from t where num=20 5.in and not in should also be used with caution, otherwise it will result in full table scans, such as:Select ID from t where num inFor consecutive values, you can use between instead of in:Select ID from t where num between 1 and 3 6. The following query will also cause a full table scan:Select ID from t where name like '%abc% 'To be more efficient, consider full-text indexing. 7. If you use a parameter in the WHERE clause, it a

), is occupied 100 characters of space, if it is varchar such a variable length field, NULL does not occupy space.You can set the default value of 0 on NUM, make sure that the NUM column in the table does not have a null value, and then query:Select ID from t where num = 03. Try to avoid using the! = or 4. Try to avoid using or in the WHERE clause to join the condition, if a field has an index and a field is not indexed, it will cause the engine to discard using the index for a full table scan ,