sql joins in r

This article explains how to split an SQL statement with one or more left JOIN or right join into multiple SQL statements. MySQL query efficiency is very low, especially large data, and high concurrency, the index can not solve the problem, the best way is to split the SQL statement into multiple single table query SQL

handling of column fields SQL Case Do the column processing Sql> Select deptno,sum (SAL) from the EMP Group by DEPTNO; Select Case When deptno=10 Then ' ACCOUNTING ' When deptno=20 Then ' Reserch ' When deptno=30 Then ' SALES ' End sum (SAL) from EMP GROUP BY Deptno handling of column fields SQL Decode There is also the case that when nothing

Today to query their own installed sqlserver2008 is R2 version, search the next, found that a lot of people query this problem, now recorded as follows, through the version of the command queryAlso understand the older brother SQL Server version of the good, a look is very clear, record 1. View SQL Server 2005/2008 version number The code is as follows Copy Code Select SERVERPR

Alias for SQL1. You cannot use the alias of the column name in the WHERE clause, that is, the select name T from EMP where t>2999; is not allowed2. Benefits of using aliases:Improve the readability of SQLImprove the efficiency of SQL parsing executionGrammar checkSemantic checkShared Pool ChecksBuild the execution treePerform3. Hard parsing and soft parsing of SQL?Execution Order of SQL1. From statement--wh

Complex SQL Split optimizationSplitting SQL is one of the most effective methods of performance optimization, which is to break down complex SQL into simple SQL by a certain logic, and finally execute an equivalent logic with the help of temporary tables, and have achieved efficient execution. I've been trying to write

1. View the version of the database SELECT @ @version Several common SQL Server patched version numbers: 8.00.194 Microsoft SQL Server 2000 8.00.384 Microsoft SQL Server SP1 8.00.532 Microsoft SQL Server SP2 8.00.760 Microsoft SQL Server SP3 8.00.818 Microsoft

1. View the version of the database SELECT @ @version 2. View the machine operating system parameters of the database EXEC master.. xp_msver 3. View Database Startup Parameters sp_configure 4. View Database Startup time Select CONVERT (varchar, login_time,120) from master. sysprocesses where spid=1 To view the database server name and instance name print ' Server Name ... ...: ' + CONVERT (varchar (), @ @SERVERNAME) (@, @) print ' Instance ... ...: ' + CONVERT (varchar) (@ @SERVICENAME)., D., ".

server| Data | database | statement 1. View the version of the databaseSELECT @ @version2. View the machine operating system parameters of the databaseEXEC master.. xp_msver3. View Database Startup Parameterssp_configure4. View Database Startup timeSelect CONVERT (varchar, login_time,120) from master. sysprocesses where spid=1To view the database server name and instance nameprint ' Server Name ... ...: ' + CONVERT (varchar (), @ @SERVERNAME), ".print ' Instance ....: ' + CONVERT (varchar), @ @S

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SQL % found, SQL % notfound, SQL % rowcountWhen executing the DML (insert, update, delete) statement, you can use the following three implicit cursors (the cursor is an area in the memory that maintains the query results, which is opened when DML is run, when it is finished, use SQL % isopen to check whether it is enab