单索引情况 # Extra值 : using where explain select * from test02 where a1='' order by a1; # Extra值 : using where;using filesort explain select * from test02 where a1='' order by a2; drop index indx_a1 on test02; drop index indx_a2 on test02; drop index indx_a3 on test02;...
mysqlINSTR 小于0mysqlin_use大于0 目录SQL优化**分析SQL性能执行计划EXPLAIN**typeposible_keys、keykey_len索引的长度refrowsExtra优化案例单表优化双表优化多表优化索引失效原则优化方法SQL排查--->慢查询日志分析海量数据锁机制主从复制 DDL自动提交 DML提交MYSQLQuery Opiimizer优化器MYSQL逻辑分层连接层–>提供与客...
SQL is a language with a syntax all its own, consisting of statements, clauses, and other pieces of code such as operators that establish parameters for limiting the query. An SQL statement is a complete piece of code that goes to a database management system, or DBMS, in order to perfo...
Structure of PL/pgSQL Supported PL/pgSQL statements Materialized views Materialized view queries Automatic query rewriting to use materialized views Materialized views on external data lake tables Refreshing a materialized view Automated materialized views Using a user-defined function (UDF) in a materiali...
In MySQL 3.23 this function is case- insensitive, while in 4.0 it’s only case-insensitive if either argument is a binary string. INSTR(str,substr) Returns the position of the first occurrence of substring substr in string str. This is the same as the two-argument form of LOCATE( ), ...
As we saw how this LIKE operator works with SELECT and DELETE, in the same manner, we can use this with the UPDATE command as well for filtering out our records. Two other operators, SUBSTR and INSTRIG, also work with string values for filtering out records. In real-time cases like, ...
The decode function can be used in SQL for and IF-THEN-ELSE construction. It's an alternative for the CASE statement which was introduced in Oracle 8. Syntax: decode( expression , compare_value, return_value, [,compare, return_value] ... [,default_return_value] ) ...
ExampleIn both arguments of this function are empty, it returns 1 −SELECT '' SOUNDS LIKE ''; We get the output as follows −'' SOUNDS LIKE '' 1ExampleIf the either of the arguments of this function is NULL, it returns NULL −...
InStr InStrRev Unirse Lcase Left Len LTrim Mid Reemplazar Right RTrim Espacio Dividir StrComp StrReverse ToString Espacios UCase Microsoft.VisualBasic.DateInterval (Para obtener más información, vea DateInterval Enum) Año Trimestre Mes Día WeekOfYear Día laborable Hora Minuto Segundo Microsoft...
Custom code in the <Code> element of a report definition RDL backward compatibility mode for SQL Server 2005 Reporting Services custom report items Named parameters in expressions such as DateFormat or NameSpace Resolution When RDL Sandboxing is enabled, only certain classes and methods ca...