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set is small, then the default as the appearance, a in each record to go to B scan again, actually swept the number of rows equal to a result set row x B result set row number. So if the two result sets are large, the result of the join IS bad.SQL Server 2005 Added merge Join, if the Join field of table A and table B is exactly the field of the clustered index, then the order of the table is lined up, as long as the two sides of the row, the cost of
IntroductionA few days ago to do such a thing: a game has an activity page, the Activity page has a product, the product below to show the actual number of views, it is equivalent to the user every request for the total number of visits will be added once, the problem is simple, each time you browse to the database to do "+1" operation. But when I do, I can dilute the SQL request and reduce the number of "+1" requests due to the fact that the total nu
options, which are related to the growth of transaction logs:Truncate log on checkpoint(This option is used for sql7.0. in SQL 2000, the fault recovery model is selected as a simple model)When the checkpoint command is executed, if the transaction log file exceeds 70% of its size, the content will be cleared. This option is often set to true in the development database.Auto shrinkRegularly checks the database. When the unused space of database files
We have to do not only write SQL, but also to write good performance of SQL statements.(1) Select the most efficient table name order (valid only in the rule-based optimizer):The Oracle parser processes the table names in the FROM clause in a right-to-left order, and the FROM clause is written in the final table (the u
is often necessary to join another table in order to satisfy one condition. In this case, using EXISTS (or not EXISTS) will usually improve the efficiency of the query. In a subquery, the NOT IN clause performs an internal sort and merge. In either case, not in is the least effective (because it performs a full table traversal of the table in the subquery). To avoid using not, we can change it to an outer join (Outer Joins) or not EXISTS.Example:(Efficient) SELECT * from EMP (base table) where
record to go to B scan again, actually swept the number of rows equal to a result set row x B result set row number. So if the two result sets are large, the result of the join IS bad.SQL Server 2005 Added merge Join, if the Join field of table A and table B is exactly the field of the clustered index, then the order of the table is lined up, as long as the two sides of the row, the cost of this Join is equal
, then the default as the appearance, a in each record to go to B scan again, actually swept the number of rows equal to a result set row x B result set row number. So if the two result sets are large, the result of the join IS bad. SQL Server 2005 Added merge Join, if the Join field of table A and table B is exactly the field of the clustered index, then the order of the table is lined up, as long as the t
) Nested Loop Join (3) Hash Join SQL Server 2000 has only one join mode--nested Loop join, if a result set is small, then the default as the appearance, a in each record to go to B scan again, actually swept the number of rows equal to a result set row x B result set row number. So if the two result sets are large, the result of the join IS bad. SQL Server 2005 A
problem is not found on Sql2005, but it should be noted. - , SQL Server three ways to connect tables (1) Merge Join (2) Nested Loop Join (3) Hash Join SQL Server 2000 has only one join mode--nested Loop join, if a result set is small, then the default as the appearance, a in each record to go to B scan again, actually swept the number of rows equal to a result
) NESTED LOOP JOIN (3) HASH JOIN SQL Server 2000 has only one join mode--nested LOOP join, if a result set is small, then default as the appearance, a in each record to go to B scan again, actually swept the number of rows is equivalent to a result set row XB result set row number. So if the two result sets are large, the result of the join IS bad. SQL Server 2005 Added merge JOIN, if the Join field of tabl
sets are large, the result of the join IS bad. SQL Server2005 New Merge Join, if the Join field of table A and table B is exactly the field of the clustered index, then the order of the table is lined up, as long as the two sides of the row, the cost of this Join is equal to the result set row of a table plus the result set row number of B table, one is plus, One is multiply, and the merge join effect is m
Usage of SQL stored procedure cursor loop and How to Use cursor to write a simple loop, stored procedure cursor The cursor and WHILE can be used to traverse each record in your query and pass the required fields to the variable for corresponding processing. ============================ DECLARE @A1 VARCHAR(10),@A2 VARCHAR(10),@A3 INTDECLARE CURSOR YOUCURNAME FOR SELECT A1,A2,A3 FROM YOUTABLENAMEOPEN YOUCURNA
functions, such as in Pl/sql languages. You can write triggers that take advantage of regular expression functionality to validate, generate, or extract values. The next example shows how you can apply the Regexp_like operator to data validation in a column check constraint. It verifies the correct social Security number format when inserting or updating. Social Security numbers in formats such as 123-45-
Tags: ISP Set add example pre Library generate own articlethe advanced Way of T-sql: 2 Levels above the base: Write subqueries Gregory Rassen (Gregory Larsen), 2016/01/01 (first published: 2014/01/29) the series This article is part of the stair series: the staircase leading to T-sql: Beyond the Basics From his ladder to T-SQ
character. Table 2 provides a complete list of repeated operators. Note that it contains special repeated options, which provide greater flexibility than the existing like wildcard. If you enclose an expression in parentheses, this effectively creates a subexpression that can be repeated for a certain number of times. For example, a regular expression B (an) * A matches Ba, Bana, banana, yourbananasplit, and so on. Oracle Regular Expression implement
Tags: block floor from Sele amt Concat Digital STR EndBecause the project needs to get (the sum of occurrences in this quarter)/(number of days in the quarter) data (plus monthly average, average annual data). Judging the time of the season is a difficult point, the beginning of the time to write a bunch of cases when to judge the month, and then write the discovery, it is too stupid. So I began to think of
accesses to the database: Oracle has done a lot of work internally: Parsing SQL statements, estimating index utilization, binding variables, reading chunks, etc. (8) Reset the arraysize parameters in Sql*plus, sql*forms and pro*c to increase the amount of retrieved data per database access, the recommended value is 200 (9) Use the Decode function to reduce proc
SQL statement for help, do not know how to write. I now have two tables A and B table A table has a field is Zhanghao,mobile, b table has zhanghao,username,address, now there are a total of 15 data, B table has 20 data, I want to table A and B table the same field values are inserted into the third list, The extra five data is also inserted into the third table, that is,
corresponding Flagid to 1, and then according to the loop to find satisfying conditions equal to 0, you can see that each cycle once, the processing of the recordset will be less once, and then the loop to select a good schedule to insert, until the recordset's bar number is 0 o'clock stop loop, this completes the operation. Comparing the application of the above several cyclic methods, you will know that sometimes we can implement different methods
Tags: example statement form HTM iteration accept using toolkit onlySQLite generation Write, SQL execution statement generationSQL Assignment 2 (20%)Questions:1. Produce a table showing the total books that is currently "checkedout" by every major. Show theMajor and ' Total Books checkedout ' in the query result and sort the ' total Books checkedout ' inDescending order. Use only the Mediacode in the Where
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